Got myself a slightly worrying trouble code on my 2001 Z06 today. I've done a fair bit of searching on the forums here and elsewhere, and it sounds to me like an internal PCM malfunction.

Anyway, thought I'd post on the off-chance anyone with a 2001-04 C5 has had similar. There are other/similar codes for the earlier C5, but this one is unique to these years.

The symptoms and my observations are:
- Check engine light came on after first starting from cold
- Car drives fine, no engine running issues, and appears to have full power
- Stop car, then re-start, which cranks more than usual, before firing
- Car drives fine, but check engine light stays on
- Stop car, pull codes and see P1683 H C (Historic and Current)
- Clear P1683 H C
- Start car, no check engine light, car drives fine
- Stop car, pull codes and see P1683 C
- Start car, no check engine light, car drives fine
- Stop car, start again and check engine light is back

I suspect I probably need to prepare for a PCM replacement, although the fact it had the same P1683 Historic code, suggests it has happened before and cleared it-self. I have never checked for codes before, and never had a check engine light, so this is a first for me!

Anyway, I'm currently cleaning off the two earths on the chassis rails up front, although struggling to separate the wiring block to clean the internals right now.

Thanks for reading. I'll let you know if cleaning the earth solves it.

If anyone else has had similar, please do reply.

 

I think one thing you need to do the next time you drive it. LEAVE
the car running, before you kill it, pull the codes again and see what is coming up.

You might pull the PCM and inspect for water intrusion and make sure it's nice and dry... maybe use a blow dryer and leave to air out in the house for a few days.

 

Quick question bud... the battery acid seems to be more common and possibly more lethal to the pcm than water intrusion... is that a valid statement?

 

Thank you sir

 

Thanks guys, for all the replies. I will try getting the codes whilst running, when I've finished cleaning the earths. I've finished working on it for the evening now - i'm a few hours ahead of you in the UK.

The condition of the battery looks good to me, so hopefully no leaks, under there. Think i will extract it tomorrow and check underneath. I had a new AC-Delco fitted by the Chevy dealer shortly after i bought the car back in 2007. The car doesn't have too much corrosion. It did go through one Michigan winter with me, before i shipped it back to the UK. It then sat outside for a few years under cover, but it is now garaged and rarely sees rain/salt. Still only has 26k miles too.

 

Bit of an update:

Cleaned the two main chassis rail earths at the front, and another under the battery. Lifted battery, and inspected underneath, nothing damaged as far as I can tell.

Put it all back together. Checked for codes and NO PCM CODES, so I thought it must have been successful, as it had cleared itself. I checked this first without engine running, and then with it running, and there were no new codes.

So, went for another 20 minute drive, and all seems fine, but then I get home and before shutting the car down check for codes, and P1683 C is back, but no other new codes. Still no Check Engine Light though. However, that just requires shutting down and when restarting the CEL is back!

Argh!! I guess I'm going to have to monitor it and expect some engine running/starting problems in the future. Hopefully I can find someone with the right GM scanner in the UK to see if there is some sort of test procedure for the PCM.

 

If you need it, I have a contact for you in the UK for a shop who can do PCM testing and/or preprograming for you in case you need to replace it.

I worked with a guy there in the past on a bad PCM issue and they took care of it for him.

My info is at home.

 

Thanks 8vette7. I will probably have a look at doing this tomorrow.

Thanks dadaroo. I've seen your thread helping V8_YEA. Please do let me know the contact details for the guy that helped with his PCM issue. I have one conctact here which i may try and that is Ian Allan Motors.

 

I did quite a bit more testing this morning. When i cleared the code, and went for a drive of about 20mins/8miles, checking for codes whilst driving continually shows no codes. But then shutting off and checking with just the ignition on shows the code has returned. It seems it needs a couple of cycles, such that the code shows an H aswell as a C, before it will illuminate the CEL.

I've decided to drive the car a bit more to see how it develops. Plus i have a Classic Car Rally event planned for next Sunday, so i'm hoping to use it for that. Then it will be time for a more detailed inspection of the PCM. I'm planning calling the one specialist tomorrow.

One other thing. I have a 7+yr old AC-delco battery (fitted by the dealer), which I think is in pretty good condition. It tests at 12.6 volts or more. I've always looked after it, so it's never gone flat and regularly is hooked up to a CTEK trickle charger. I'm debating whether it is worth replacing as a precaution too.

 

Does not seem like the battery is an issue if it is at 12.6 and you have no charging issues while you drive.

Here is the shop link, you need to contact the OP for more info on the shop.

https://www.corvetteforum.com/forums...ering-mph.html

 

Thanks dadaroo. I have read and re-read that thread a few times. Quite a complex issue that guy had, but with the cause also being a faulty PCM, which I understood as likely being due to a battery acid leak.

I may well get in touch with him and the guy that was able to flash the new PCM. They are both users of another forum i use in the UK (Pistonheads). Think the guy that helped him specializes in tuning the Aussie GM Monaro and other cars sold over here. He also posted on our Corvette Club website over here, offering tuning services using EFiLive.

Thanks for all your help.