[turbo2ltr]

2018 SS 1LE with 7k miles. Was planning on selling it this week. Drove fine two days ago for the test drive. This morning I start it (It has a battery that is less than 6 months old) and I get a "service rear axle" message. I googled it and seemed its a common issue to pop up once in a while. But along with the message, I hear noises from the rear of the car (I haven't moved yet).

I try a few restarts, and the message still appears. Seems to continually pop up while running.

I went to the back to try and figure out where the noise was coming from. I initially assumed it was some solenoids or something in the e-diff. but it turns out its the driver side exhaust valve wigging out. Passenger side seems fine.

https://youtu.be/HjLcQ6RWKcw

Seems very odd that the two issues would appear at exactly the same moment when the car has been running flawlessly up until this point.

No check engine light.

Any ideas?

[CalgaryZL1]

My guess is it’s pissed off, because it’s only been driven a little more than 1k per year? Maybe disconnect the battery for 10 or 15 minutes see if it smartens it up

[Gunkk]

"Service rear axle" is a common false-positive fault when the system goes low voltage (commonly from a dead battery). Solution: disconnect the battery from the car and charge it up with a battery charger/tender. Reconnect, boot up the car in service mode, clear the bogus CEL codes, then start normally.

[turbo2ltr]

Originally Posted by Gunkk

"Service rear axle" is a common false-positive fault when the system goes low voltage (commonly from a dead battery). Solution: disconnect the battery from the car and charge it up with a battery charger/tender. Reconnect, boot up the car in service mode, clear the bogus CEL codes, then start normally.

From what I've read, the message, when caused by a low voltage issues, is a one time message. This has been popping up on every start and appears to be continuously triggered when the car is running. The battery is less than 6 months old and is fully charged.

I'll have to look up the service mode thing. Wasn't aware there was a service mode.

[speedyink1]

Did something chew a couple wires?

[turbo2ltr]

Originally Posted by speedyink1

Did something chew a couple wires?

Very doubtful. I've lived here 20 years and never had any evidence of rodents.

I left the battery disconnected a few days. Still the same thing.
The message definitely seems tied to the valve issue. It only pops up when I hear the valve. Also oddly, seems to fix itself when you put it into gear (M/T). Not sure if that was just coincidence but I did it a couple times.

The buyers bank wanted an emissions test, but I just disconnected the battery. I've already had major issues trying to get the evap test to run to the point where it was unregistered for 6 months until I moved out of a emissions area and didn't need one. So that deal went south.

The stealer is looking like the only option here. I cringe just thinking about it.

[rickr9504]

Originally Posted by turbo2ltr

2018 SS 1LE with 7k miles. Was planning on selling it this week. Drove fine two days ago for the test drive. This morning I start it (It has a battery that is less than 6 months old) and I get a "service rear axle" message. I googled it and seemed its a common issue to pop up once in a while. But along with the message, I hear noises from the rear of the car (I haven't moved yet).

I try a few restarts, and the message still appears. Seems to continually pop up while running.

I went to the back to try and figure out where the noise was coming from. I initially assumed it was some solenoids or something in the e-diff. but it turns out its the driver side exhaust valve wigging out. Passenger side seems fine.

https://youtu.be/HjLcQ6RWKcw

Seems very odd that the two issues would appear at exactly the same moment when the car has been running flawlessly up until this point.

No check engine light.

Any ideas?

It happened exactly the same to my 2018 2SS 1LE and it spent 3 months at the dealer, and they couldn't figure it out. I got so pissed, I sold it thinking I could buy another one, but it was in the middle of covid, and I couldn't find any that matched what I wanted. Now, I can't find anything at all. I'll wait for another car similar that makes me happy to drive.

[turbo2ltr]

Originally Posted by rickr9504

It happened exactly the same to my 2018 2SS 1LE and it spent 3 months at the dealer, and they couldn't figure it out. I got so pissed, I sold it thinking I could buy another one, but it was in the middle of covid, and I couldn't find any that matched what I wanted. Now, I can't find anything at all. I'll wait for another car similar that makes me happy to drive.

Guess I'll take the hit and sell it as is.

[dpevans]

Wonder if you have some moisture in the trunk and have some the green wire crusties. Or maybe like a harness shorting to ground when ever the valve acts up. I really hate electrical issues. I would start by inspected every wire harness in the trunk and then under the rear end starting at the NPP.

[Mark114]

Originally Posted by turbo2ltr

I went to the back to try and figure out where the noise was coming from. I initially assumed it was some solenoids or something in the e-diff. but it turns out it’s the driver side exhaust valve wigging out. Passenger side seems fine.

Originally Posted by turbo2ltr

I left the battery disconnected a few days. Still the same thing. The message definitely seems tied to the valve issue. It only pops up when I hear the valve. Also oddly, seems to fix itself when you put it into gear (M/T). Not sure if that was just coincidence but I did it a couple times.

Have you tried swapping the NPP actuators to see if the problem with the exhaust valve moves with the actuator? Maybe you just need to replace the actuator?

[turbo2ltr]

Originally Posted by Mark114

Have you tried swapping the NPP actuators

No but that was my next troubleshooting step. I'm in the middle of moving and the car is at one house while all my tools are at the other house 2.5 hours away. I also had not researched if the two sides were the same part numbers

Additionally I found that there is a calibration for them in a service tool menu. I could see a low battery in the right conditions maybe scrambled the calibration. So looking at that avenue as well. That also means that the issue may get worse or at least present mixed results if you swap the actuator without recalibrating it.

Haven't given up yet...

Wonder if you have some moisture in the trunk

Unlikely. This car has never been in the rain and full time garaged. And Live in Phoenix where the humidity is extremely low. But couldn't hurt to poke around back there and make sure there isn't any issues. The trunk does contain a box of sulfuric acid in the form of a battery. Though the vent is properly connected. The old batter I took out 6 months ago had some crusties around the cell plugs.

[Vtor_ZL1]

Wiring damage in rear wheel wells ?

[turbo2ltr]

So I bought a "Creader Elite G" scan tool. Interface is a little clunky but I got it because google showed me a corvette forum thread that showed it had the MPP relearn ability.

I was able to do the relearn, but all it did was change the way it makes noise.

Long story short, after seeing the hidden DTC with the chassis control module and the rear diff module that all had to do with communications and voltage levels, coupled with the turn signal randomly flashing fast and then normal, I am leaning towards a wiring issue....somewhere.

Edit: I also feel like even in touring mode, the TC was allowing a significant amount of rear tire slip. Going around 90 deg turns, the e-diff screen never showed more than 1% slippage which seems odd as well but I don't really remember what it normally shows.

[CalgaryZL1]

Do you have cheap ass LED lights anywhere on the car if so check them first.