It was time for the annual state inspection. Everything was working fine, scan shows P1111 Ready, so off I go to the inspection station. They hand it back to me with a fail on the 3rd brake light. When I get in the car, its in limp mode, gearbox fault and check engine light. Shut it off and restart, the gearbox fault is gone and no longer in limp mode, but CEL still lit. Scanned it when I got home and the only code is P1642, indicating a CAN bus error. I've got 15 days to fix the brake light or pay for the inspection all over again. But the light itself is fine, just not getting any power when the brake pedal is applied so it must have something to do with the CAN bus error. I've read several posts suggesting that P1642 is often left after connecting to a scanner (perhaps one such as used at the inspection station). I suspect the technician or the inspection station computer was at fault somehow, but of course I could never prove that and the car is not even worth the cost of a lawyer anyway. I found one cryptic post that seemed to indicate that someone had run into this exact situation before but it did not provide the solution or even any leads. I have not cleared the code yet, as erasing the DTCs with my basic $100 scanner also resets the emissions monitors and going through the full drive cycle in mixed traffic around here is risking ones life and limb which I hope to avoid. And I haven't removed the whole back seat yet to check the wiring as I'm guessing it must be related to the CAN bus and the problem is unlikely to be in the wiring loom under the package tray. Any insight would be appreciated.

 

The third brake light isn't connected to the other brake lights. It is controlled by the Body Processer Module. If you are not getting power a possibility is the wiring harness that is mounted on the left side hinge in the trunk. A broken wire there will cause it not to light. The flexing from opening and closing cause the wires to develop breaks. Do your trunk lights work? Probably not same wiring harness.

 

Well I never would thought to check that, but yes, all the lights on the trunk lid work fine, as does the power latch.

 

The HMSL relay is in the boot fuse/relay box.

Jump across the 30/87 (3/5) contacts to see if the lamp illuminates?

 

Thanks. That did not light it up. The fuse was blown. But why? Can't imagine them connecting their scanner would blow that fuse? Weird. Now any way to clear that 1642 without also clearing the emissions monitors?

 

I made an error earlier the wiring is behind the plastic shield on the right hand hinge not the left. My oops.