I was contacted yesterday by a lady, recently widowed, that has had several warning lights come on in her '06 vert. I checked out the car, first driving the car enough to see how it drives, get the drivetrain fully warmed up (oil temp around 200F and transmission temp aruond 150 or so), then cleared out a laundry list of codes in several systems. Re-started the car, and the following issues remain:

Rear tire pressure sensors are not reporting: LR display is blank, RR displays "XX".
PCM: P0121 "Throttle Pedal Position Sensor/Switch "A" Circuit Range/Performance. I didn't see any driving symptoms, just this code.

ABS: C0121: Valve relay circuit malfunction. Best I could find was that this shows an EBCM failure. Question: is there any way, other than a Tech 2, to cycle the EBCM to see if it's just sticky after sitting for an extended period of time?

Vehicle Immobilizer codes, C0755, C0765 I didn't find anything useful on these codes. One interesting symptom: The car never saw the key fob (which could lock/unlock the car), but would let me drive the car without issue! Hmmm.

The closest dealership that I feel good sending her to is around 60 miles away, and she's been burned by other dealerships in the past. So I'd like to clean as much up as possible before we head that route.

Thanks for any help, and have a good one,
Mike

 

 

The throttle position code was coming up on mine too. It ended up being the throttle pedal/sensor. I bought one from my local dealer (after waiting 3 months for one from GM parts Direct) for $130.00. Easy to change and solved my problem. I was also getting a "reduced power" message on the DIC. The TPMS sensors are available on ebay for $100 for a set of four. If you go that route make sure you are buying TPMS sensors recently made. Some are original and made years ago and the little battery inside has a limited lifespan. As far as your fob, I think there is a battery inside of it as well. If that isn't it, the receiver is probably bad...not a high dollar part either. I have owned 2 C5's and now have a 2006 C6 and have managed to fix everything my self so far. Good luck! These are great cars when they are right!

 

Forgot to add, I have fixed my cars myself with a LOT of help from the folks on this forum. Great people great knowledge. They actually do know what they are talking about...Thanks for all of your helpl!!!

 

Make sure the battery is 100%......

 

i think P0121 is a throttle position sensor code, Personally i would start with replacing the throttle position sensor or the whole throttle body, not sure if you can service just the sensor, i'm sure google will tell you.
The thing you stomp on with your right foot is an accel pedal, not a throttle.

C0755 is a right front low tire pressure sensor problem, replace TPMS.
C0765 is a right rear rear tire pressure sensor problem, replace TPMS.
I'm sure a pattern emerged, replace all 4 TPMS.

Can't help with C0121.

 

And both terminals are tight and clean.

 

How old is the battery. Might make sense to replace.

 

Thanks, everyone, for your responses. Here's a couple of things to clarify:

1. These codes were recorded after driving the car for about 30 minutes, so I'd consider the battery to be fully charged
2. I don't know the age of the battery
3. The text I recorded for the diagnostic codes was verbatim out of the Blue Driver diagnostic tool.
4. The first step with fixing the TPMS problem is to replace all 4 sensors, as y'all recommended
5. The first step I'm going to take regarding the EBCM is to flush out all of the (probably original) brake fluid. This isn't perfect for getting the fluid out of the EBCM, but it's cheap and I don't own a Tech 2. Assuming this does NOT fix the problem (I give it <50/50 chance), next step is to find a Tech 2 to try cycling the unit to see if it frees up.

Thanks again for all the help, and have a good one,
Mike

 

So make sure on the TPMS sensors that they have been manufactured recently. I see so many of these items on EBAY and other corvette parts websites, but a lot of them are already DOA because they are old stock that remains unsold. I bought a set of new old stock sensors that were not good out of the box. Good luck..hope you figure out the problem.

 

Your not listening about the battery. Aged battery can throw codes and cause all kinds of ills.

 

Yes, I understand about the battery. Remember this isn't my car, I'm helping a lady out. There are things I just don't know yet about this car. I hope to figure more stuff out this weekend if I can get back with her.

Have a good one,
Mike

 

What's being said, without being direct, is the first thing to do (after replacing the tpms sensors) is put a KNOWN GOOD battery in the car, erase the codes, then drive it again to see if the codes come back. Don't waste any other money before doing this. That is hopefully clear and direct enough.

 

Serious question: what do you mean by "good"? Start the car normally (i.e. not sluggish)? Start the car without voltage going below xx?

TIA, and have a good one,
Mike

 

If you don't want to buy a new battery, take one out of a car that is not giving issues and temporarily swap it into the car for the test.

You cannot know for sure that the battery that is in the car is good, even if it load tests as good. The only way to eliminate the battery as a source of the issue is to remove it from the car and use a different battery. Weak and/or bad batteries cause all kinds of electrical code gremlins in these cars.

 

Remember, this isn't my car. I'm trying to help out a recently widowed lady who wants to keep the car after her husband died. And, if taking a battery out of a car that isn't giving problems (my C5 is my only side-post donor) is an answer to my question of "what do you mean by 'good'", then that makes sense to me. I'll give that a try. That also has the benefit of letting me pull her battery and give it a good once-over, and gives her car a chance to reset the systems.

Have a good one,
Mike

 

Yes, I understood it's not your car. Just trying to potentially save some money and headaches chasing nonexistent issues by starting you with looking at the most common item that typically causes multiple codes on these cars. The tpms codes are a no-brainer.

 

 

Even without all the codes, if she does not know that the battery has recently been replaced, she needs a new battery. Then if the codes go away, end of story. If not then they can be addressed.