Emissions System

[oldandslowformula]

Anyone have experience with getting the secondary air system monitor to complete readiness for emissions?

This is a NA2 02+. I've been doing drive cycles per the suggestions online. All the other emission monitors seem to ready fairly quickly after an event that resets them, simply just after going on for a short drive. The last one that is giving me problem is just the secondary air system.

I read that the ECU checks this system only during cold starts and I've been doing plenty of cold starts (atleast 15-20 times) then go for a short drive. Can someone confirm this for the NSX? I can hear the secondary air system turn on for about 30 seconds each time. There is no check lights or codes of any kind. I use a OBD2 scanner.

Does the actual temperature and how cold the vehicle is matter? The weather here has been hot and "cold starts" are actually around 70 degrees ambient in my garage in the morning. This is my only other thought where the vehicle comes up to temperature too quickly.

Appreciate any suggestions on how to diagnose.

 

[Old Guy]

First off, emission monitors are a bitch! There appear to be no standards for the emission monitoring routines implemented by different OEMs so the monitors appear to differ. That is why there is not a guaranteed single drive cycle that will get you 'there'. Generally there is no publicly available information for the monitors with the exception of a document that I discovered from Ford describing their monitor strategies.

Your description of the secondary air system pretty much describes what I experience on my 2000. Temperature does matter according to the service manual.
- the engine coolant temperature must be between 0C and 70C The 0C bit is confusing because I have started my car below freezing and I am pretty sure the air pump was running. Also, that kind of implies that fast heat up of the catalyst is not required when it is really cold which would seem like the time when you want it most.
- the engine coolant temperature has to have dropped by > 20C from the time that the engine was previously stopped
The running time is a maximum of 60 seconds; but, can be reduced based upon engine coolant temperature and intake air temperature. The SM provides no guidance on what those temperature sensitivities are. Note that these are the conditions for the secondary air system to run which is not the same as completion of the monitors.

There are a number of DTCs directly associated with the secondary air system.
P0410
P0411
P1410
P1415
P1416

Since these are later additions to the OBDII error code set, make sure that your scanner can actually report these error codes. Even if you do not have a CEL illumination, check for stored error codes. If you have any stored codes with respect to the secondary air system I expect the ECU will not execute the monitor routing. If you do have stored codes, clear them, cross your fingers and try a start where the engine matches the only two conditions that Honda has listed.

The Honda secondary air system is used to meet the LEV standard. The Ford document I have is for their LEV-II emission monitor and their system does not use a secondary air system to achieve compliance. The Honda secondary air system was a bit of a bandage. More modern engines use cam phasing as part of their cold start strategies. That said, I have screen grabbed the entry conditions for the Ford LEV-II monitor to complete.


Note that it refers to catalyst temperature. This is not actual catalyst temperature; but, an inferred catalyst temperature based on an algorithm which takes a number of other engine measurements into consideration. Also note that the minimum entry temperature for the monitor is 35 F which is a nudge above that 0C that the service manual notes so maybe that is the minimum temperature for the monitor to execute.

Successful completion of the Ford monitor is based upon the catalyst reaching a specified change in temperature (expressed as a temp at finish over temperature at start ratio) which is an inferred temperature. According to the Ford document the inputs to the inferred temperature calculation are engine speed, measured air mass (I assume they are a MAF engine) and commanded spark. Ford provides no guidance on how the algorithm uses this to calculate an inferred catalyst temperature. It would seem reasonable that since the objective of the secondary air system is to get the catalyst hot quickly that Honda might be using a similar inferred temperature calculation which means that failure to pass the monitor could be caused by an error or problem with one of those other inputs used in the inferred temperature calculation.

Assuming you have no stored DTCs relative to the secondary air system, are you letting the secondary air pump finish operation first before driving or are you driving off shortly after starting the car? I might try that as a variation and then checking the monitor status while the engine is still hot. As a Hale Mary you could clean the IAT because Honda's MAP system uses the manifold air temperature to infer air mass - that is assuming that Honda uses an inferred catalyst temperature for the air injection monitor Honda does state that the pump running time is a function of IAT so IAT problems could screw the system up.

That is my wild assed guess at what goes on with the secondary air monitor. All else fails, slaughter a chicken and sprinkle the blood on the car at mid night under a full moon to see if that helps.

 

[Bram]

I think the IAT need to be cleaned or replaced

Bram

 

[oldandslowformula]

First off, emission monitors are a bitch! There appear to be no standards for the emission monitoring routines implemented by different OEMs so the monitors appear to differ. That is why there is not a guaranteed single drive cycle that will get you 'there'. Generally there is no publicly available information for the monitors with the exception of a document that I discovered from Ford describing their monitor strategies.

Your description of the secondary air system pretty much describes what I experience on my 2000. Temperature does matter according to the service manual.
- the engine coolant temperature must be between 0C and 70C The 0C bit is confusing because I have started my car below freezing and I am pretty sure the air pump was running. Also, that kind of implies that fast heat up of the catalyst is not required when it is really cold which would seem like the time when you want it most.
- the engine coolant temperature has to have dropped by > 20C from the time that the engine was previously stopped
The running time is a maximum of 60 seconds; but, can be reduced based upon engine coolant temperature and intake air temperature. The SM provides no guidance on what those temperature sensitivities are. Note that these are the conditions for the secondary air system to run which is not the same as completion of the monitors.

There are a number of DTCs directly associated with the secondary air system.
P0410
P0411
P1410
P1415
P1416

Since these are later additions to the OBDII error code set, make sure that your scanner can actually report these error codes. Even if you do not have a CEL illumination, check for stored error codes. If you have any stored codes with respect to the secondary air system I expect the ECU will not execute the monitor routing. If you do have stored codes, clear them, cross your fingers and try a start where the engine matches the only two conditions that Honda has listed.

The Honda secondary air system is used to meet the LEV standard. The Ford document I have is for their LEV-II emission monitor and their system does not use a secondary air system to achieve compliance. The Honda secondary air system was a bit of a bandage. More modern engines use cam phasing as part of their cold start strategies. That said, I have screen grabbed the entry conditions for the Ford LEV-II monitor to complete.
View attachment 194084

Note that it refers to catalyst temperature. This is not actual catalyst temperature; but, an inferred catalyst temperature based on an algorithm which takes a number of other engine measurements into consideration. Also note that the minimum entry temperature for the monitor is 35 F which is a nudge above that 0C that the service manual notes so maybe that is the minimum temperature for the monitor to execute.

Successful completion of the Ford monitor is based upon the catalyst reaching a specified change in temperature (expressed as a temp at finish over temperature at start ratio) which is an inferred temperature. According to the Ford document the inputs to the inferred temperature calculation are engine speed, measured air mass (I assume they are a MAF engine) and commanded spark. Ford provides no guidance on how the algorithm uses this to calculate an inferred catalyst temperature. It would seem reasonable that since the objective of the secondary air system is to get the catalyst hot quickly that Honda might be using a similar inferred temperature calculation which means that failure to pass the monitor could be caused by an error or problem with one of those other inputs used in the inferred temperature calculation.

Assuming you have no stored DTCs relative to the secondary air system, are you letting the secondary air pump finish operation first before driving or are you driving off shortly after starting the car? I might try that as a variation and then checking the monitor status while the engine is still hot. As a Hale Mary you could clean the IAT because Honda's MAP system uses the manifold air temperature to infer air mass - that is assuming that Honda uses an inferred catalyst temperature for the air injection monitor Honda does state that the pump running time is a function of IAT so IAT problems could screw the system up.

That is my wild assed guess at what goes on with the secondary air monitor. All else fails, slaughter a chicken and sprinkle the blood on the car at mid night under a full moon to see if that helps.

Thank you for the comprehensive response. It gives me some ideas on what to look out for because I could not find much information. I browse Prime regularly and search through the threads and can usually find what I need, this topic required a new post.

I think my vehicle is within the parameters most of the time for the secondary air system to start. Even though it's been warm weather, I hear it turn on. This is after at least 5 hours with the vehicle sitting or overnight. Ambient temperature being 70 - 90 degrees. I let the vehicle come up to temperature with each drive cycle which should be 190+ degrees coolant temp.

I actually just assumed that my OBD2 scanner was able to read secondary air DTCs but now that you mentioned that, I am not sure. It is fairly new but a cheapo $50 Innova 3210RS. I cannot find whether it can or cannot read these DTCs.

I was wondering how the system reads catalyst temperature or detects the system to clear the monitor. Did not think of the IAT. I will look to clean that. Yes, I do let it idle until the secondary air system goes off before driving. I few times I did mix in driving it prior to, or throttling up for higher RPMs to see if there is any difference, simply because I had no other ideas lol.

 

[oldandslowformula]

I think the IAT need to be cleaned or replaced

Bram

I will try that. Thanks.

 

[Old Guy]

I actually just assumed that my OBD2 scanner was able to read secondary air DTCs but now that you mentioned that, I am not sure. It is fairly new but a cheapo $50 Innova 3210RS. I cannot find whether it can or cannot read these DTCs.

I was wondering how the system reads catalyst temperature or detects the system to clear the monitor. Did not think of the IAT. I will look to clean that. Yes, I do let it idle until the secondary air system goes off before driving. I few times I did mix in driving it prior to, or throttling up for higher RPMs to see if there is any difference, simply because I had no other ideas lol.

You could try just disconnecting the solenoid that controls the valve that opens and closes to admit air ahead of the catalytic converters. That should generate a trouble code. If your scanner reads the trouble code then it will probably do the trick.

I don't 'know' that catalyst temperature is involved in Honda's version of the monitor or that they use a similar algorithm to what Ford might use. But, the fact that Honda states that air compressor run time is affected by intake air temperatures suggests that the IAT is in the mix - somehow. In addition to cleaning it I would use an ohmmeter to check its resistance to make sure that it has not gone out of spec.

 

[acuhon]

There is recommended driving cycle . This is from Smolketips for Pilot and worked for me on 97NSX.


In most cases, your vehicle's emission monitors should run during normal driving on both city and highway traffic conditions and over the course of 200 to 300 miles. However, due to different driving habits, the criteria required to run a monitor may not always be met. Following the Honda Pilot drive cycle below should allow the emission monitors to complete. The drive cycle must be followed accurately.Take extra caution when performing the drive cycle on public roadways. Perform the drive cycle at your own risk. If you feel you might not be able to perform the drive cycle safely, or obey all traffic laws, seek the assistance of a smog check repair station which will be able to perform the drive cycle on a dynamometer, utilizing specialized OBD II drive cycle readiness tools/scanner/computer.

Emission "monitors" are internal self-tests which the engine control unit (ECU) performs to ensure your Pilot is not polluting and is running efficiently. The entire process of self-testing various emission control systems is called a Drive Cycle.
[h=2]How To Perform a Honda Pilot Drive Cycle[/h]The following is a Honda OBDII Drive Cycle Pattern. (Obey all traffic laws while performing drive cycles. Perform acceleration steps only on highways)
COLD START: Begin from Cold Start, and ignition in OFF position for at least 1 hour. Insure your Honda’s fuel tank is between 1/4 and 3/4 full and engine coolant temperature must be below 122°F and within 11°F of the ambient air temperature. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
IDLE TIME: Run your Honda’s engine (do not drive) for 2 1/2 minutes with the air conditioner on and rear defroster on. During this period the ECU will be running the Oxygen Sensor Heater self-test, Air Injection System Passive Air test, EVAP Purge "No Flow" test, Misfire Detection.
ACCELERATE: Turn off the air conditioner and rear defroster and begin driving. As soon as possible apply half throttle until 55mph is reached. The ECU will now run self-tests on the Misfire Detection, Fuel Trim, and EVAP Purge Flow.
HOLD STEADY: Now hold your vehicle speed steady at 55mph for three minutes. During this time the Oxygen Sensor O2 response, Air Intrusive (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim diagnostics will be performed.
DECELERATE: During this step you want to slowly let off the accelerator pedal. Do not brake or shift your Honda in order to slow down. It is important to let the vehicle coast along gradually slowing down to 20 mph. The ECU will once again self-test the EGR System, EVAP Purge System and Long Term Fuel Trims.
ACCELERATE: Go ahead and accelerate again at 3/4 throttle until 55-60mph is reached. This will perform the same self tests as during the first acceleration step.
HOLD STEADY: Hold steady speed once again. This time at 55mph for five minutes. During this time, in addition to running the self-tests as during the first HOLD STEADY step, the ECU will perform the catalyst monitor diagnostics. If the catalyst (Catalytic Converter) is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst,or in order to Complete the CAT Monitor.
DECELERATE: This will perform the same diagnostics as in the first Deceleration. Remember not to press your Honda’s brake or shift gears during deceleration.
This should complete the drive cycle on your Honda Pilot. To ensure all monitors are complete use a scan tool to view the monitors. You may want to complete the drive cycle 2-3 times.

 

[Old Guy]

Only rub is that the Pilot does not have a secondary air system (I used to have a 2003 Pilot) and your 1997 does not have a secondary air system and it is the secondary air system monitor that is the one that is not completing for the OP. The secondary air system is a 2000+ addition to the NSX to qualify for the LEV standard.

 

[oldandslowformula]

There is recommended driving cycle . This is from Smolketips for Pilot and worked for me on 97NSX.


In most cases, your vehicle's emission monitors should run during normal driving on both city and highway traffic conditions and over the course of 200 to 300 miles. However, due to different driving habits, the criteria required to run a monitor may not always be met. Following the Honda Pilot drive cycle below should allow the emission monitors to complete. The drive cycle must be followed accurately.Take extra caution when performing the drive cycle on public roadways. Perform the drive cycle at your own risk. If you feel you might not be able to perform the drive cycle safely, or obey all traffic laws, seek the assistance of a smog check repair station which will be able to perform the drive cycle on a dynamometer, utilizing specialized OBD II drive cycle readiness tools/scanner/computer.

Emission "monitors" are internal self-tests which the engine control unit (ECU) performs to ensure your Pilot is not polluting and is running efficiently. The entire process of self-testing various emission control systems is called a Drive Cycle.
[h=2]How To Perform a Honda Pilot Drive Cycle[/h]The following is a Honda OBDII Drive Cycle Pattern. (Obey all traffic laws while performing drive cycles. Perform acceleration steps only on highways)
COLD START: Begin from Cold Start, and ignition in OFF position for at least 1 hour. Insure your Honda’s fuel tank is between 1/4 and 3/4 full and engine coolant temperature must be below 122°F and within 11°F of the ambient air temperature. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
IDLE TIME: Run your Honda’s engine (do not drive) for 2 1/2 minutes with the air conditioner on and rear defroster on. During this period the ECU will be running the Oxygen Sensor Heater self-test, Air Injection System Passive Air test, EVAP Purge "No Flow" test, Misfire Detection.
ACCELERATE: Turn off the air conditioner and rear defroster and begin driving. As soon as possible apply half throttle until 55mph is reached. The ECU will now run self-tests on the Misfire Detection, Fuel Trim, and EVAP Purge Flow.
HOLD STEADY: Now hold your vehicle speed steady at 55mph for three minutes. During this time the Oxygen Sensor O2 response, Air Intrusive (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim diagnostics will be performed.
DECELERATE: During this step you want to slowly let off the accelerator pedal. Do not brake or shift your Honda in order to slow down. It is important to let the vehicle coast along gradually slowing down to 20 mph. The ECU will once again self-test the EGR System, EVAP Purge System and Long Term Fuel Trims.
ACCELERATE: Go ahead and accelerate again at 3/4 throttle until 55-60mph is reached. This will perform the same self tests as during the first acceleration step.
HOLD STEADY: Hold steady speed once again. This time at 55mph for five minutes. During this time, in addition to running the self-tests as during the first HOLD STEADY step, the ECU will perform the catalyst monitor diagnostics. If the catalyst (Catalytic Converter) is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst,or in order to Complete the CAT Monitor.
DECELERATE: This will perform the same diagnostics as in the first Deceleration. Remember not to press your Honda’s brake or shift gears during deceleration.
This should complete the drive cycle on your Honda Pilot. To ensure all monitors are complete use a scan tool to view the monitors. You may want to complete the drive cycle 2-3 times.

I've been doing this drive cycle and others that are similar. No luck on the secondary air system.

Per the suggestions, I pulled the IAT last night and cleaned it. It was pretty dirty. I've done two drive cycles so far from cold starts. No luck yet.

 

[Old Guy]

Did you check to confirm that the resistance of the sensor was within spec?

The Ford document indicates a minimum time for the entry conditions for the monitor to run, 11 seconds. Honda might have a similar requirement. If it is so warm where you are that the secondary air system is not running very long that time requirement might be blocking the monitor from setting. But, I have no idea whether Honda has that requirement and if it does how long that time requirement might be. Where I live overnight temperatures drop enough that the secondary air system is running for a significant period of time on first start.

If you cannot get the monitor to set after the first start of the day I am going to speculate that you will not get it to set on successive starts because I don't think I have ever heard the secondary air system start up on subsequent starts in the same day unless it is really cold.

Is this an issue that you need the monitor set for an emission compliance test? If so, check and you may find that the regulatory agency will give you an exemption for setting of certain monitors. I know some will do this for the Evap monitor because those have a reputation for being really cranky to set and they might do it for the secondary air monitor. They will not give you an exemption if you have any trouble codes displayed or stored. I believe you have to apply for this exemption. It might be worth checking with your state regulator rather than trying to beat yourself up trying to find the magic combination that sets the monitor.

 

[oldandslowformula]

Did you check to confirm that the resistance of the sensor was within spec?

The Ford document indicates a minimum time for the entry conditions for the monitor to run, 11 seconds. Honda might have a similar requirement. If it is so warm where you are that the secondary air system is not running very long that time requirement might be blocking the monitor from setting. But, I have no idea whether Honda has that requirement and if it does how long that time requirement might be. Where I live overnight temperatures drop enough that the secondary air system is running for a significant period of time on first start.

If you cannot get the monitor to set after the first start of the day I am going to speculate that you will not get it to set on successive starts because I don't think I have ever heard the secondary air system start up on subsequent starts in the same day unless it is really cold.

Is this an issue that you need the monitor set for an emission compliance test? If so, check and you may find that the regulatory agency will give you an exemption for setting of certain monitors. I know some will do this for the Evap monitor because those have a reputation for being really cranky to set and they might do it for the secondary air monitor. They will not give you an exemption if you have any trouble codes displayed or stored. I believe you have to apply for this exemption. It might be worth checking with your state regulator rather than trying to beat yourself up trying to find the magic combination that sets the monitor.

I have not check the resistance but I can figure out how to do that later. The IAT seems to be reading correctly though. Using the live data feature on the scanner, before first start this morning IAT was 76 degF and ECT was 75 degF. Seemed reasonable with ambient conditions. Would a out of spec sensor show temps way off?

The secondary air system only would start the same day with many hours between. I've also been looking at info for the S2000 as well, the folks over there say you need 2 drive cycles to set S2000 secondary air system: 1 cold start followed by 1 warm. Don't know if this applies to NSX but been trying that as well. Alot of similar experiences with S2000 regarding secondary air monitor issues.

Yep, smog for registration. Evap is not required here but secondary air system is required.

 

[oldandslowformula]

Also, I inspected the vacuum lines and air pipes and they seem okay. Could there be something wrong with the air pump itself that would cause the monitor not to set? I'm wondering if it's worth accessing the quarter panel to inspect the air pump for anything obvious that could be affecting performance. The Ford example shows 50 deg min change in catalyst temp. A leak or poor performing system may fail to meet this criteria?

Again, my scanner shows no DTC. I'll try to go confirm it using another scanner. The CEL does blink 5 times which I think is related to emissions for Acura vehicles. Someone correct me if I'm wrong because I could not easily find this in the manual.

 

[docjohn]

Thank goodness we removed all that ULEV piping from my 00 transplant. Although I doubt my 96 ecu would care if it worked or not.

 

[Old Guy]

If the IAT and ECT readings are close pre start then the IAT sensor is probably OK.

The air pump has a current sensor on it connected to the ECU which I expect the ECU uses to confirm that the air pump is operating. From the current level it measures I would expect that it would be able to infer how much air is actually flowing or whether it is blocked by a secondary air valve failure. If there was a problem with the air pump or the control valve I would expect that one of the secondary air system DTCs would cause the CEL to illuminate.

I don't remember seeing a catalyst temperature probe so as far as I am aware it does not directly measure catalyst temperature. If the inputs that it uses to infer catalyst temperature are correct then it assumes the temperature is correct and the system is working. Theoretically the air injection pipe could be disconnected from the manifold and not injecting air and it might measure out as being OK and allow execution of the monitor. Like if the EGR tubing gets plugged; but, the EGR valve is still working the EGR monitor passes; but, the car fails its NOX test. That said, since we really do not know how the secondary air injection monitor works and since nothing else seems to be yielding the desired result physical inspection might be useful.

The Ford system uses mass air flow. The NSX MAP fuel injection infers mass air flow using the intake air temperature, the manifold air pressure sensor, engine speed and a fudge factor called volumetric efficiency. If the MAP sensor or the engine speed had measurement errors that could screw things up; but, if there was a problem with the crank speed sensor or the MAP sensor I would think you would have a whole bunch of other driveability issues that should be quite obvious. I suggested check the IAT sensor just because crud contamination on the sensor is a known problem and the errors can be subtle. At this point I have kind of shot my wad and if there are no DTCs indicating component problems it may be just a matter of driving around until the cows come home.

I used to check the status of the monitors on my 2000 every spring when I took the car out of winter storage. I would start the car up, check the tires and check for leaks and noises and if everything was OK drive the 20 km from the storage compound to my home. Plug the OBDII scanner in and check to confirm that everything was set. Never had to do any extraordinary drive cycle things to get the monitors to set. Mystery as to why some cars have so much trouble with the monitors.

 

[oldandslowformula]

I agree. I think if the air pump is working with no DTCs the monitor should be able to clear. I pulled the pipe at the control valve and its blowing pretty good airflow when pump is on. I also double checked all the vacuum lines in that emissions box that holds the solenoids and everything seems correctly connected.

If the NSX is not measuring anything downstream in the exhaust than agree with your theory of anything being disconnected or how much air is actually being pumped probably doesn't matter for the monitor to clear. I recently put in a new MAP sensor so I'm confident it is reading correctly. For other vehicles, people mention replacing the O2 sensors; I recently replaced those too. But no information on the NSX says it uses the O2 sensors for this. Car is running with no issues.

I also left the car outside for the last 2 nights since weather is cooler and started it in the mornings at around 60 degF ambient. The air pump stayed on for 45 secs and 51 secs. The manual said 60 secs max. No luck yet.

Can Acura techs or others force the monitors to ready?

 

[Old Guy]

I am not aware that the Acura techs can force the monitor to show complete in part because Honda uses the K data line on the OBDII connector which is pretty limited in its functionality. You can ask; but, I expect the answer is no and they will give you a copy of some drive cycle.

Since you put a new MAP sensor in did you install an OEM sensor or an aftermarket sensor? Was the car completing the secondary air monitor prior to the MAP sensor being replaced? Was the previous sensor dead or causing significant issues? If not dead or seriously out of whack I might be inclined to try the old one if you still have it and see what happens.

Even though you do not have any error codes, there are stored and pending error codes. Sometimes the presence of those codes can prevent completion of a readiness monitor. Can you use your scanner to check for pending / history codes? Doing a hard reset on the ECU will clear all that stuff; but, for now I recommend against that because it will also clear the completed status on the other monitors and if they don't set that may make life worse.

 

[oldandslowformula]

I installed an OEM sensor. No, I think the prior MAP worked fine too, but the secondary air monitor was not ready then either. This is a "new to me" vehicle btw. I put in new MAP, O2 sensors, and injectors to tune it up because it was showing lean fuel trim DTCs and I want to start refreshing the vehicle. After that I did a DTC clear. The fuel trim is showing slightly rich (-7 to 10%) on Bank 1 now at idle but no DTCs for many drive cycles and ~150 miles. Car runs normal to me but will continue to look into the rich condition because that looks a bit high. Again, rich seems to be only at idle.

Can someone confirm that Honda/Acura does not use the O2 sensors for the secondary air monitor, like some other manufacturers do? I replaced them and they work fine but trying to see if that secondary air monitor is possibly related to fuel trim at idle.

 

[Old Guy]

The fuel trim is showing slightly rich (-7 to 10%) on Bank 1 now at idle

Is that short term trim or long term trim? Short term trim would probably be less of an issue.

I have the service manual supplement for the 2000 model year which covers the diagnostics associated the secondary air system. I don't recall any refences in the service manual supplement referring to the O2 sensors in the trouble shooting for the secondary air system. There should be a 2002+ service manual supplement for your car. If you can find one there may have been changes to the secondary air system and the procedure for diagnosing problems with the secondary air system in the supplement may give you a better idea as to what is going on.

 

[oldandslowformula]

long term trims, but largely because I would let the car idle for 10 minutes or so. If I drove immediately it should be much lower. I've been looking at the live data to study this; under load its fairly normal and at idle may show rich. Though again, no lights at all for too rich. But I'm not sure why its showing rich for idle.

I'm just wondering if the secondary air system monitor is relying on O2 sensors to clear monitors.... Just confusing

 

[Old Guy]

A final thought on the secondary air system monitor problem. The secondary air system injects air into the exhaust manifold as part of the process of heating up the cats fast. I am presuming two possibilities
- the ECU goes into a super rich mode so that there is unburnt fuel exiting the exhaust port to mix with the injected air and be burnt to heat up the cat
- the normal warm up enrichment is enough that it results in unburnt fuel exiting the exhaust port which is mixed with the injected air and is burnt to heat up the cat

I don't know where this burning takes place. In the header or in the cat. Depending on where this excess air is burnt, the ECU monitor might be checking the primary O2 or secondary O2 sensors to confirm that something is taking place. Depending on where the combustion is occurring it could be looking for high O2 or lower O2. Two things could screw this up
- the injectors are dirty and are not injecting the correct amount of fuel when the secondary air system is running resulting in high O2 measurements
- the O2 sensors are reading incorrectly

During start up the engine is not in closed loop operation so it cannot correct for a problem with the injectors. If the injectors have never been cleaned on the car I might be inclined to have this done because having the injectors cleaned on a car that is 20 + years old would never be a complete waste of money.

All of this is pure speculation because Honda does not share how the secondary air system actually works (where the burning takes place) and what the conditions are for the completion of the monitor.

 

[Bram]

Just a thought.....Did you replaced the O2 Sensors with OEM units or aftermarket one?

Bram

 

[oldandslowformula]

Thanks for the responses. I'll do some more diagnostics when time allows. I did confirm that the car does not have any pending/history codes, or any DTCs at all with another scanner.

Yes, just odd that Honda would not give any monitor readiness procedures for the NSX. I was not able to find anything more in the supplemental service manuals. That's why I been looking at the S2000 and other honda vehicles that have the secondary air system. Procedures in those service manuals seem to be on the lines of, "Cold start and let idle for 1 minute, readiness code should switch from incomplete to complete. If not, check for temp DTCs. If no DTCs, repeat again". Another would be "Idle for 20 seconds, Rev to 2000 rpm and hold for 3 minutes, than idle again 20 secs". To me, this would indicate that the honda secondary air monitor should run its diagnostics during the first few minutes, but still very poor procedures.

For other vehicles, such as domestic brands, BMWs, Porsches, information says secondary air relies on o2 sensors and possibly both o2 sensors across cat converter. And the monitor could run at a later time much after the cold start. Confusing. Some even reports ECU problem or software not causing the onboard diagnostic monitor to run. That would suck...

I replaced the pre-cat o2 sensors with NGK NTK brand. The post-cat o2s are denso. The o2s seem to be reading fine, looking at the voltage in the live data. Also, if they had issues I would think I'd be experiencing other issues or DTCs relating to O2 or fuel trims. Engine is stock, no mods, btw.

 

[Old Guy]

If not, check for temp DTCs. If no DTCs, repeat again".

Did those procedures advise on which temperature sensor to check?

I pulled the pipe at the control valve and its blowing pretty good airflow when pump is on.

I assume that this is at the inlet to the air control valve? Did you ever check to confirm that the air control valve is actually operating, not stuck open or stuck closed? The description of the DTCs implies that the ECU monitors the air control solenoid valve ( which controls the air control valve); but, does not directly monitor the operation of the air control valve. If you have a hand vacuum pump you could apply it to the air control valve control line and then blow on the inlet to the valve to see if it opens and closes as you apply a vacuum.

 

[oldandslowformula]

Did those procedures advise on which temperature sensor to check?



I assume that this is at the inlet to the air control valve? Did you ever check to confirm that the air control valve is actually operating, not stuck open or stuck closed? The description of the DTCs implies that the ECU monitors the air control solenoid valve ( which controls the air control valve); but, does not directly monitor the operation of the air control valve. If you have a hand vacuum pump you could apply it to the air control valve control line and then blow on the inlet to the valve to see if it opens and closes as you apply a vacuum.

Sorry "temp" meaning temporary. This language is from the s2000 service manual.

Yes, I disconnected it at the air control valve, but could not easily visually see whether it's opening or closing from where it's located.

 

[Old Guy]

You can't visually see whether the valve is opening or closing. You would have to test.