This 2008 Chevrolet Avalanche came in with the complaint that the right front turn signal did not work. This article applies to Avalanche, Escalade, Silverado, Sierra, Suburban, Tahoe and Yukon trucks and suv’s. This generation of GM truck or Suv does not use a turn signal flasher relay as we have always known in the past. Instead the turns signal switch sends a signal to the BCM and and the BCm then sends a pulsing signal to the turn signal bulbs in the front and rear of the vehicle. If the vehicle has turn signals built into the side view mirrors it also sends the same signal to that light as well. If the BCM is at fault for a front turn signal not working check to see if the matching signal in the side view mirror is working. If it is the BCM is doing it’s job and the problem will likely be in the bulb, socket or wiring. This vehicle did not have that option so pinpoint testing was going to be needed. I went ahead and located wiring diagrams and pinout locators for the BCM connectors. Did I mention that I had already tested at the light assembly and the signal circuit was missing. The bulb and socket were okay. Also there were no codes in the BCM data stream and controlling the light with the scan tool produced the same results.
Even though there is not a separate fuse for the right front turns signal circuit I decided to check all of the fuses anyways. This is what I found. The courtesy light fuse in the driver’s side interior fuse box was blown.
Power on one side of the fuse …
… and no power on the other side.
The 15 amp fuse was blown. and is shown below.
Now the turn signal is back working again. In the GM and Mitchell wiring diagrams for the exterior lights/turn signals there is no mention of the courtesy fuse being involved in the turn signal operation. It is shown in supplying power to the BCM though in the power input diagrams. No real reason was found for the fuse being blown but it does have a new radio and other add ons in the cab of this truck. I suspect that the fuse was blown when this stuff was installed. I informed the customer that the fuse may blow again and if it does we will need to look at it again to locate that problem.
Just one more reminder to stop guessing and start testing.