P0175 Code after maintenance

[baggelis]

I recently had mayor maintenance done on my 04 that has around 25k miles. I replaced the following:
timing belt, tensioner, valve cover gaskets, oil pan gaskets, spark plugs, fuel pump, fuel filter, all relays as recommended by nsxshop, all fluids (coolant, transmission, clutch, brake), one of the O2 sensors, a/c and alternator belts, clutch from SOS. The only mod in the car is a complete CT engineering header/exhaust system.

I just got around to driving it and after approximately 35miles it throws code P0175 that can be caused by a list of things. From previous experience do you guys think it can be related to the timing belt change or it can have something to do with the o2 sensor replacement?

This is only active code at the moment.

Regards,
Evangelos

 

[Old Guy]

Which O2 sensor did you replace and why? P0175 is the 'running rich' code for the front primary O2 sensor. If that is the sensor that was replaced during maintenance then the problem may have existed prior to doing the maintenance. First thing to do would be to determine which sensor was replaced and why so that you can rule out a pre existing problem. A leaky / drooling fuel injector on the front cylinders can also cause this code; but, that would also tend to fall into the category of a pre existing problem.

Valve clearance and presumably valve timing can cause the code, so a one tooth out timing belt error might cause the problem; however, I have no direct experience with that. If the maintenance records do not point to a pre existing problem then checking the timing belt position / valve timing would be prudent.

I am curious about the statement

all relays as recommended by nsxshop,

What is that about? Is that something more than the usual paranoia about the main FI relay?

 

[baggelis]

Thanks for the prompt response. I am figuring out which o2 sensor was replaced to see if it matches the code as suggested (I replaced it because of an error code suggesting malfunction). If the timing belt was off by a tooth wouldn't it cause more error codes besides the P0175?

The relays replaced are the 4 as listed in the following link:
https://www.thensxshop.com/1991-2005-na1-na2-nsx/oem-honda-nsx-relay-4-piece-set

 

[Old Guy]

There is nothing in the ECU monitoring system that directly monitors the status of the timing belt. The OBD II codes are primarily mandated by US emission laws and monitor things that could alter the emission performance of the engine as they wear. The system is designed to flag problems that cause the car to become non compliant with the emission standards. The OBDII system is not designed to detect assembly errors (which is what an error on the timing belt set up would be).

Valve clearance is considered a wear issue and valve clearance is only in the possible cause list because if it is dramatically out of spec it can alter how complete combustion is which can then cause something like P0175 which is a fuel mixture out of range error which means the engine is probably no longer compliant with emission standards. Presumably a slight error in the timing belt position could create similar circumstances to incorrect valve clearance which is why I speculate that an assembly error when replacing the belt might be a possible cause of the error code.

Checking the timing would not be super difficult; but, does involve taking some stuff apart. I would definitely rule out the possibility that the problem existed prior to carrying out the maintenance before doing the timing belt check.

Interesting note on the relays. I understand the paranoia around the main FI relay failure, particularly on earlier cars although starting to fail at 15,000 km does seem a really big stretch. I am not so sure that its warranted for later cars. The other 3 relays are 'news to me'. I am not aware of anybody describing them as high failure rate items. Keep the originals in a spare parts baggy. With only 25,000 miles on the car I expect that they are probably good for another 50 years. A lot of the relays on the NSX are interchangeable so if something like a Blower High relay packs it in one of those other three relays might be a perfect fit.

Edit:
Depending on the type of timing belt error (one or more cams, all the cams, how far out), you may also get ignition misfire error codes. Of course, get the timing belt far enough out and you will get the 'bent valve' error code .

 

[baggelis]

I guess the 4 relay replacement was not a wise decision...

Anyway, I am aware that there is no code for a timing belt error but since it was replaced and one of the possible reasons for the code is valve adjustment my mechanical common sense says that it could have something to do since an engine with only 25k miles would not have significant wear to merit a valve adjustment. This is the reason I asked on the first place, to see if someone has previous experience with a similar issue.

I just checked and the previous cel I got was for rear secondary O2 sensor (Bank 1, sensor 2) which I think rules out the possibility of a previous condition with the fuel system.

 

[docjohn]

You had a lot of work done and ...in Panama.....PM this guy...http://www.nsxprime.com/forum/member.php/3729-Larry-Bastanza

 

[Old Guy]

I guess the 4 relay replacement was not a wise decision...

Maybe yes, maybe no. I have just never heard of issues with those other three relays.

Since the previous O2 sensor replacement was for the rear secondary sensor, I agree that it is not obvious that the P0175 code is a due to a condition that existed prior to the maintenance. Its probably prudent that the timing belt covers be pulled so that you can confirm the timing. I think if the belt tensioning is done incorrectly, this can alter the timing; but, I thought that would primarily affect the rear cylinders (I stand to be corrected).

If the timing belt checks out OK and you have access to a good code scanner use the code scanner to display the short and long term fuel trims when the engine is warmed up and has gone into closed loop operation. In a perfect world, all the trims would be close to 0%. Since you are generating a 'system rich' code on the front sensor, check for large negative numbers in the long term fuel trim on both the front and back. Consistent large negative front and back fuel trim numbers would be a sign of a fuel problem that could be excessive fuel pressure. Large numbers on just the front could be a sign of a drooling injector on the front.

 

[docjohn]

I'm sorry but I had to chuckle at "drooling injector"...that was my nickname at the local gentleman's club....

 

[baggelis]

thanks, I will check timing belt “set up” and fuel trim

 

[Old Guy]

I'm sorry but I had to chuckle at "drooling injector"...that was my nickname at the local gentleman's club....

This is causing my mind to go many places.

 

[baggelis]

Forgot to mention that the fuel pump was replaced with a walbro 255 from SOS.

 

[docjohn]

" it is by docjohn alone I set my mind in motion"........a geeky movie reference :redface:

 

[Old Guy]

Forgot to mention that the fuel pump was replaced with a walbro 255 from SOS.

Was a fuel pressure check done at the time the pump was replaced? Excessive fuel pressure can cause the P0175 code and would likely show up as high - trim values.

 

[baggelis]

No, no fuel pressure check was done. I’ll check fuel trim first and if it checks out I lo have the timing checked

 

[baggelis]

Most recent event:
when I was heading for the shop the engine would die if I would accelerate and then come to a stop or put my foot of the pedal but it could still hold idle rpm after I turned it back on.

 

[Larry Bastanza]

Definately check fuel pressure

 

[baggelis]

All right guys, just to let you know the fuel pressure was within limits. It turns out my mechanical common sense was right. We removed the engine from the car and checked the timing and it was off, corrected it and now it drives like a champ, thanks for the input.

 

[Old Guy]

All right guys, just to let you know the fuel pressure was within limits. It turns out my mechanical common sense was right. We removed the engine from the car and checked the timing and it was off, corrected it and now it drives like a champ, thanks for the input.

Owe - that is expensive / a hassle. Out of curiosity, why did you pull the engine just to check the timing?

 

[baggelis]

This was the first time performing this task and we wanted to make sure that everything was as per spec (better safe than sorry) so we went the extra mile. I don’t know if you are familiar with the timing belt change but it is quite difficult because of the limited access.

 

[Old Guy]

Yes, I know the process and if the engine is out I agree 100% that it is much easier to do. However, dropping the engine / raising the car is no trivial task, particularly for those who don't have access to a hoist. Also, disconnecting & connecting things can result in damage so I like to keep that to a minimum. If I was just checking timing I would do the minimum to facilitate the check; but, once you find an error I guess you are almost into a complete redo.