Hello,

After driving for about 15min in 4wd, switch light on "4wd" button starts
flashing and "service 4wd" message appears on instrumental panel, 4wd
desingages. It'll work again after you turn the engine off and let it stay for
some time. Dealer claims it has DTC c0379 code set ($80 to read that code)
and front differential actuator ($400) and 4x4 mode switch ($140) have to be
replaced. Can anyone give me an advice how to make sure they don't replace
perfectly working parts before I shell out almost $1000?

Thank You.

Welcome to AF.No mention of year here, but both the dash switches have been problematic. Might try that first and see what happens, but if they scanned this and commanded 4x4 operation on the scanner, they would see which components were unresponsive in their diagnosis.

Thanks Maxwedge,

Yes sorry, Tahoe is 2003. I was just sceptical two expensive components
fail at the same time. Judging by the symptoms (turning 4wd on is never a
problem, it sometimes turns off by itself after 15-20min) my theory was low
fluid level, overheating or some such.

You mean using scanner they can reliably tell this part is broken even without
physical access to it? What if it's just electrical contact and not part itself?

Interestingly, after their diagnostics 4wd works fine so far, drove for an hour
with 15min break and it was OK.

Thanks.