Pablo Ceballos

Hello everybody, I purchased used a C7 Z06 A8 and after one day of using it a message with service satbilitrack, service rear axle and electric power steering disconeected were constantly displaying in the dashboard.
The car is under warranty so I took it to the dealership and they have replaced the rear diff, the rear diff module, the EMBC module and a front brake sensor and still nothing.
After 4 and a half months they still don't now what'ss wrong with the car and this is becoming very frustraiting, so I'm coming up to you guys and see if anybody knows who could help me with that.
I live in Mexico City so that makes it even more complicated I guess, but any suggestions are welcome.

Vetteman Jack

Moved to C7 Tech.

laserdude2215

Codes?

Pablo Ceballos

these are the current ones: U042B, U0428, U0077

laserdude2215

Those are communications codes related to the chassis control module located to the left of the battery. So either the module is bad, has no power or ground, or the chassis high speed LAN wiring is bad.

Pablo Ceballos

Thanks Laserdude, and this is the tech version:
He says he checked the high speed LAN wiring and it is ok, the chasis control module is brand new too(the last part they changed) and the ground was ok as well... so kinda stuck there.

laserdude2215

Can you have the tech measure the resistance between pin 12 and pin 13 on the data link connector?

RonC7

Do the errors show up as soon as you start the car? How old is the battery? Low voltage at startup can cause comm errors.

Ron

Pablo Ceballos

Well the technician said he could not provide me any more info...so I think the only thing left to do for me now is to either prey or get the car out of the dealership and solve it on my own.
In your experience fixing any of the mentioned issues:
Would you say it is going to be super costly and thus it is better to wait and see? or will it be a quick cheap fix so I should do it on my own?

Pablo Ceballos

FInally they agreed to give me the information... the resitance between pins 12 and 13 is 60 ohms
Also 6 and 14 is 60 ohms.

As the tech describes the problem: Every time he turns left to get out of the shop he gets the message on the cockpit of service stabilitrack and service rear axle.... at very low speed. And this is basically the same messages since the begining. No advanements after changing all the parts they have already exchanged.

Regarding the battery he claims it has more than half of useful life.
Maybe this gives you some insight on where we are.
Any help is highly appreciated guys... this is driving me nuts.

laserdude2215

I'm just making a guess, but have the tech check the wheel speed sensors and the steering wheel angle sensor using the factory scan tool (GDS2) or equivalent. These are inputs to the EBCM.

laserdude2215

Here's another guess. Measure the resistance between pin 12 and pin 13 on the data link connector while slowly turning the steering wheel from stop to stop.

The symptoms and the codes all point to a problem with the chassis high speed LAN.

ersatz928

Could be a chassis ground issue somewhere. Especially check the ground wire/bolt for the electric steering rack. This thing takes big slugs of current when turning the steering wheel at low speeds. Also check the power feed bolts at the 12V power distribution/fuseblock, located between the engine compartment fuse/relay box and the coolant tank. There is a black plastic cover that that needs to be popped off the top of it.

Pablo Ceballos

According to the tech all results of that test were normal... and as you can see execution is preety slow

BrooksC7

I know this is an old post but did you ever get the issue fixed? My 14 c7 is doing the exact same thing.

Pablo Ceballos

Hi Brooks!
After a lot of time at the shop and a lot of component changes, what finally turned out to solve the problem was changing the complete harness.
So I do not know exactly where there might have been a shortcut, but I am pretty convinced it was a shortcut rather than the e-Diff or some module that was causing the problem all along.
If those things actually failed it was due to a shortcut somewhere in the harness.
I have had some other issues lately, and they have all been electrical issues. I have seen the cable insulation melted allowing shortcuts to happen. The last time that I had the stabilitrack message in my dashboard (2 months ago) it was solved by changing the battery...
So I would start with the harness, ground connectors, etc and then move to other areas like modules or the E-Diff.
Hope that helps!
Regards!

BrooksC7

thanks for the reply. I guess, I'll just re check all the plugs and grounds. My issue started after changing exhaust header gaskets so I thought it was a plug or something but it all looked good. This car is so finicky

Tinkertech

Problem occurred when turning left.

That was the key.

Intermittent or short due to flexing wire harness.

Just like you found.