I have a '17 3LT Grand Sport - dashboard lights flicker on/off and the gauges (mph, fuel, temp) drop to zero for several seconds before returning to normal. The heads-up display, A/C and bluetooth connection also shut off while gauges are at zero and then pop back on when the gauges return to normal. There is also a "Service Rear Axle" warning that pops up independent of the dash flicker. Occurs frequently and not associated with speed, bumps, turns, etc. Dealer has updated all computer systems and no errors show in diagnostics - they are calling GM TAC. Anyone know why/how to resolve?

 

When electrical gremlins pop up and seem random, the usual culprit is the battery. I suggest you have the battery checked. Old batteries act stupid when they are on the way out. How old is the battery?


Elmer

 

A lot of these things dropping out like this can be power or ground related…I looked at a wiring diagram for a 2017 and it looks like it’s may not be ground related…looking at the power distribution there are a few circuits you mention being fed from the logistics fuse and power for that fuse comes from the Ignition Main Relay….if the BCM loses power that controls the coil side of the relay from the BCM that can do it…the ground for the coil side of the relay is G100 which is on the right side of the engine block....looks like the Bluetooth is fed from the Human Machine Interface module…also the HUD and maybe if the Rear Differential Clutch Module loses power for a second that may throw the Service Rear Axle message…I can’t find any info on the “Aux” HVAC Control Module which is separate from the HVAC module…the Dealership's ALWAYS call GM TAC if it’s something more involved than diagnosing a headlight bulb…VERY SAD !!…they should be putting a scope on all 4 terminals of that relay and while driving see what may be dropping out…a scope is part of their required tooling but they ONLY use it for NVH (Noise, Vibration, Harshness) and nothing else…I’ve been using a scope for 13 years and it is my “Go To” piece of diagnostic equipment and is necessary to diagnose cars today…try swapping that relay with another 5 pin relay or buy a new one and see what happens…ask the dealership if they used a scope on your concern ??…bet you a million dollars they didn’t !!

 

There is a small gauge wire attached to the negative battery cable. The wire often breaks when the big negative wire is removed. Service rear axle is a common symptom of that.

@C5 Diag post is right on. There are two grounds on the frame left side of the engine. You can see them when you open the hood. I have seen those bolts work loose.