Bogus CELs

[Yellow Rose]

First off, for Drew, the "correct" acronym is MIL. :smile:

Is it possible for the ECU to throw fake codes? This is why I ask.

Over the past three months, my NSX has come up with three CELs. Each time I simply pulled the clock fuse to reset the ECU, because my laptop was not with me.

Over this past weekend, I experienced three more CELs.....on the same day!!! The first time the engine was at idle in the driveway when the light came on. I fired up the laptop to read and reset the CEL. It was P1204 #4 Injector Circuit Open / Shorted. Now that to me is VERY odd, because the engine was running smooth, as in not with only five injectors squirting.

I cleared the CEL and took the car for a test spin. All is fine. Return to the driveway for a belt tension adjustment. Decide to hook up the laptop for some datalogs, I was in the driver's seat configuring the data file on the laptop and the CEL light comes back on, but this time it is blinking. Pull the codes and it is two codes....P1205 #5 Injector Circuit Open / Shorted and P1300 Boost Calibration Fault. Again, the engine was running flawlessly.

Is it possible for the ECU to temporarily detect a bad reading and toss a premature code, when in fact the engine is fine?

For those that do not know, I have a 10-12 PSI (depends on my car's mood) BBSC. The P1300 code confirms BZ's comment, that the factory ECU has its own MAP sensor to compare against the factory MAP sensor in the engine compartment, at start-up and idle conditions. With the BBSC, I have the SS controller, which has its own MAP sensor. Apparently, on that particular day, the ECU's MAP sensor did not like the SS's MAP sensor, thus the code.

OK fine, but why today under the exact same barometric conditions, did I not get any CELs?

Thus my question - can the ECU throw "artificial" CEL codes?

 

[Larry Bastanza]

Hi Andy,

According to the OBDII codes the P120x is cylinder misfire, x = cylinder number.

This will occur if the system detects emmisions that can damage the cats according to the 1995 service manual. Funny, I have a 1995 here now that is giving me a P1203. Cylinder #3 is definately not acting right, but I have still not figured it out. I will get a fuel pressure gauge on it tomorrow ans see what that tells me.

In the service manual it lays out a list of possibilities, from bad compression to fuel pressure issues, to the typical bad coil, fouled plug, etc. I will jkeep you posted.

Also I beleive these are "two trip" codes that require the prblkem to occur in two consecutive "trips". They will also reset is after two more trips it is not detected.

Intermittent problems are the worst

Later,
LarryB

 

[Yellow Rose]

This will occur if the system detects emissions that can damage the cats according to the 1995 service manual.

What device is the ECU reading to detect emissions? The O2 sensor only or is there some other device that also reads NOX and HC gases? I think I saw the air-fuel ratio running a little bit rich when one of the error codes was shown, but I do not recall exactly. What I do recall is that the engine was thoroughly warmed up, so it is not like the ECU was forcing the rich condition like it does during initial warm-up. Could’ve been that the ECU sees a warm engine and a rich AFR at idle (no boost) and it got confused?

In the service manual it lays out a list of possibilities, from bad compression.....

Engine has only 25k mile, so it shouldn’t be the rings. However, the compression ratio was dropped from 10.2:1 to 9.5:1.....surely the ECU is not that smart?

.....to fuel pressure issues.....

Fuel pressure is steady 52 PSI at steady-state and 62 PSI at full-throttle.

.....to the typical bad coil.....

Ugh, something else to check - six times.

.....fouled plug, etc.

Plugs are only two years old, they should be good.

Also I believe these are "two trip" codes that require the problem to occur in two consecutive "trips". They will also reset if after two more trips it is not detected.

Same type of code (doesn’t matter which cylinder) or exact same cylinder code?

 

[Larry Bastanza]

I believe it is monitoring the 02 sensors, and it the mixture gets too rich and it cannot be trimmed within range, it will throw the code. I am not 100% sure but I think it would have to be the exact code twice to turn the light on, then twice to turn it off.

In regard to the compression, no it is not that smart, the troubleshooting guide in the service manual lists that as a possible cause for mis-fire, which is whjy I brought it up.

The 1995 I have now is running rich at idle, and the #3 cylinder is not as strong as the other cylinders at idle, but ALL electrical parts have been swapped for NEW parts, AND I have even swapped fuel injectors, and the ECU is still giving a P1203, after a drive and the car is at idle.

I am going to check the fuel pressure to see if the vacuum modulator is bad and it is idling too rich. On the road it actually feels pretty good, but at idle it is missing, and smells obviously rich.

I will see where it leads me.

Later,
LarryB

 

[MiamieNeSeX]

After our last dyno/tunning session we noticed a considerable difference in the A/F readings between the wideband and the Dyno at idle to about 4500 rpms. The uego sensors are mounted on the Comptech header factory bung locations. Could be that they are not "sniffing" enough to give a correct reading as opposed to the Dyno sensor which is basically a vaccum pump drawing in your exhaust gasses.


Armando

 

[6061-T6]

I’m interested to know if Andy or Larry identified and were able to fix the “Bogus CELs”? I’m also getting “Bogus CELs. Long posting below:

My 1995 NSX-T with BBSC/SS has been getting 71,72,73 & 79 codes. These have gone from intermittent to not being able to clear the codes recently. 7x for 71 through 76 codes are random misfire for cylinder x. 79 is spark plug voltage detection circuit malfunction. One of these was read out of the OBDII port as P1318, “Spark Plug Voltage Detection Module Reset Circuit Malfunction, Front Bank”.

Car history. “Standard” BBSC installed by MarkB in August of 2002. Car had ~17k miles at the time. I updated the SS box in the trunk twice and MB moved the SS box behind to the passenger seat at NSXPO 2003. The SS box is cracked open like a clam shell with a data/programming cable coming out of the open side. The SS box is hard wired, it does not use the break-out harness. Engine has Tiatec headers, otherwise stock. Car currently has ~43K miles. The 6 year service was performed at 9.5k miles when I purchased the car in Feb 2002. The 6 year service was also done Feb of 2004 a highly respected NSX tech in Portland, Or. Compression checked “fine” at the Feb’04 service (I don’t have the values with me). The emissions related coil replacement was done in early 2002 (I also don’t remember the specific TSB on this.)

I planned to drive from Portland area to Oakland during Thanksgiving. I got about 130 miles and the MIL and TCS lights came on. When I cleared the codes they returned immediately. After phone consultation with MB (while he was in the hospital taking care of his mom), I drove the car home. I did not detect any misfiring. Consultation included verifying proper vacuum (boost) and RPM readings from the SS box using the SS software and my laptop. At home I inspected wiring to the SS box found exposed wires at some of the crimped butt splices. I insulated these with electrical tape and the code went away. I drove the car several hundred miles without problems until (Murphy watching) the night before planning to drive to Oakland for Christmas holiday the code(s) returned. After lots of fiddling, including getting the codes from the OBDII port, I decided to replace the crimped butt splices connecting the SS box with soldered connections. This seemed to solve the problem. I drove over 525 miles of the 640 miles to Oakland and 71,72,73 & 79 codes returned and would not clear. GRRR.

I have re-reinspected wiring and cannot find a problem. I removed the serial cable from the SS box and reclosed the box. The codes are gone again and I’ve successfully driven 30 or 40 miles. I plan to take a couple of days driving coastal roads between Oakland and Portland area starting tomorrow. I hope without getting MIL. I don’t think I’ve fixed the real cause of my problem.

Happy Holidays,

Roy

 

[NSX-Racer]

I fired up the laptop to read and reset the CEL. It was P1204 #4 Injector Circuit Open / Shorted.

Hope you don't mind that I'm asking you this when you already have other problems: Is there a program with which you can read out error codes from an NSX (I have a '98 cp.) with a laptop? My techie always said he can't use it's usual diagnosis computer with my car because it has a much more simple or different diagnosis structure than modern cars - don't bash me for this, I have no clue myself.

 

[6061-T6]

http://www.obdmeter.com/index.html
http://obddiagnostics.com/
http://www.obd-2.com/
http://autotap.com/welcome.html

Are all possible sources for OBDII readers. I have not seen or used any of these.

Regards,

Roy

 

[Larry Bastanza]

6061-T6,

The car I have was restored to normal operation by cleaning the throttle body, replacement of #3 coil, and a major service. But only time will tell about the P1203 code. It may return, not sure.

In regard to your specific issue, the 71-73 are misfires for every cylinder on the REAR bank, vs. the P1318 which is the FRONT bank. It sure seems like you have a possible faulty connection somewhere. If the OBDII scanner gave you a P1319, which is the REAR bank, it would at least narrow it down to an issue common to all three rear bank cylinders (1,2,3).

Sorry I do not have more to offer here.

Regards,
LarryB

 

[Briank]

Any time you modify the stock wiring you run the chance of having bad connections. Longer wires needed for the SSbox increase the possibility of picking up noise that could mislead the ECU into thinking there is a problem. I do not know what the SS box does but I assume it modifies the cylinder/crank sensor signals to pull back the timing under boost. I would look hard at all the grounds for the engine, ssbox, and ECU. There has been a couple references here of engine ground cables left disconnected after engine servicing.