Hey everyone, I posted a while back about my electrical issues and most people said that with no experience with electrical issues that I should take it to a shop that can work on it. I took it to a shop experienced in auto electrical repairs who no longer thinks they can fix it. Started with 90% sure my "PCM" was bad is what they kept telling me and then it switched to my tune on my car was messing with it and that they wanted to put the stock c6 tune on it, and now they arent going to charge me and I just need to come get it. If anybody knows a individual or shop in Nashville TN, I could really use some help here, starting to give up on this thing. For anybody curious of what issues the car is having I will list them below, I also want to mention that the tune thats on the car has been on it from what i've been told for over a year before these issues occured.

Constant Issues:
- Car starts idles weird, and all modules show “Not Equipped” on scanner but is still drivable
(If any of the issues below happen, disconnecting the battery allows the the car to become driveable again)

Occasional Issues: ‘Hard to Replicate’
- Won’t start at all, anti-theft light shows up
- While driving anti-theft light shows up locks car in 2nd gear all gauges go crazy
- Starts all modules show “Not Equipped” and car is locked in second gear
- Car starts all modules turn on with lots of “Lost communication to modules” and “Bus communication” errors

 

With the car off and the battery disconnected (to be safe), take the following resistance measurement at the OBD2 port under the steering column:
1. Set your multimeter to read ohms.
2. Put one probe of your multimeter on pin 6, and put the other probe on pin 14 (doesn't matter which probe goes where).
3. Read the resistance value in ohms and report back here.

 

I will do this as soon as I have the car back in my possession!

 

If the car has communication issues ask them if they have looked at pins 6 and 14 at the DLC looking for 60 ohms and if they hooked up a scope to look at the comm waveforms which is pictured below and report back…testing with a scope (if they are "experienced" in electrical repair they should be using one) is essential…they should also see around 2.5 volts at pins 6 and 14 too which is pictured on my DD…with a scope they should be seeing a 0-7 volt square wave on pin 2 which is the class 2 serial data bus...is this an “auto electric” shop and not a general repair shop who is “experienced” in electrical repairs ??…that just means they can test a light bulb confidently…a diagnostic shop would work too…and NOT a dealership !!

 

On the other hand if you have the patience, you can take the car apart and test every wire yourself starting with the ground connectivity. It's your car may as well as start learning how to take care of it. From my experience with my car most of the issues are connectivity issues in the harnesses themselves. I haven't had yet much electronic problems per say (touch wood).

The harnesses/ground to start with are the outside ones, those exposed to the elements. I would suggest checking/cleaning engine bay grounds and then looking at the ECM harness next. It's easier than getting a hold of an oscilloscope, just need an ohm-meter and patience.

Checking the resistance as suggested by prior posters is part of the deal with the ohm-meter.

 

The OP has a “communication” issue so taking the car apart and testing every wire is not a good way to diagnose this…this is not an engine bay ground problem…there is a “diagnostic process” for dealing with comm issues and a DVOM and Scope is the way to quickly and accurately diagnose this…disconnecting modules one at a time can solve this…why the ECM harness ??…any bad module in the car can cause a communication problem…have you ever diagnosed one of these comm issues ??…if not you really don’t know what’s involved here…it’s not easy !!..watch any YouTube video on these comm issues and in 99.99 % of them a scope is used in the diagnosis.

 

Hi,

Yes, I had a communication issue with some of the computers of my C6. Turns out the harness going to the ECM had been sliced in the factory, not fully through, just the protection. Overtime the exposed copper strands oxidized and affected communication between ECM & BCM resulting in DTC pertaining to communication issues (lost communication with this and that component) that were going & off.

I understand your point with the scope and I agree with you on it being the best way forward but I don't have a scope and I would assume that he doesn't have one neither. In my case I tested conductivity on all grounds and then measured resistance on all the wires outside of the car (from one end of the harness until the other).

It took me 4 days but I found the faulty wire, took the harness apart to locate the issue and cut 10 inches off of the wire that I replaced with another wire. I did start with the harnesses that had devices that were complaining, it wasn't a total harness random selection thing.

If he has access to a decent shop that can do all you suggest, I'd say go for it. From my experience, there is a limit though if you don't have the right shop, I know this guy in Germany who shelled out 14k$ to find the faulty wire in his C6. My 4 days versus 14k$ was a no brainer.

Where I am, there ain't a Corvette mechanic within a thousand mile radius, so I have no choice: all issues on the car have been fixed by me start to end, the only thing I don't do is wheel alignment.



Cedric

ps: A bad/intermittent ground can affect the serial bus because the signal is matched against a reference point. Yes, if there is a defective module, you are correct, testing the harnesses won't identify the issue, it would just confirm that the harnesses aren't the source of the issue. Also, as the C6 components are often daisy chained, a defective computer in the chain is going to block the downstream dudes from reporting to HQ.

So knowing who is not reporting and looking at how these guys are daisy chained/interlinked would help in understanding where to start. Assuming the Tech2 is seeing anything ...

 

The OP is having his own shop diagnose this so I don’t expect him to get an oscilloscope…HIS shop should be using one IF they know how to diagnose this…sounds like they don’t !!

 

Yup, I agree with you on the analysis. If they don't have an oscillo / proper tool to view serial data go through, he needs another shop or may as well deal with it himself was sort of my badly phrased response because if they light bulb test the car he can do that and it won't cost him 100$ an hour ...