We recently had a Toyota Tundra brought to us by Utah Ogden Mission to diagnose an issue they were having with the park sensor system. Vehicle had recently been in a minor accident in the rear and had the rear park sensors replaced by the local Toyota dealer. Even after park sensor replacement, the vehicle's crash/park sensor system would not calibrate.
Thankfully we have an amazing Toyota mechanic on our team that loves to diagnose the concerns that most shops, including the dealer, have a hard time with.
First thing our Toyota mechanic did to diagnose the customers concern was perform an extended test drive and duplicate the customers concern. During the test drive,our mechanic was able to easily and quickly duplicate the concern of rear sensor warnings.
Once in the shop, the second step was to check for obvious problems in the area that was recently repaired. We removed the rear bumper and visually inspected the rear park sensors for any obvious damage or installation errors. We also visually inspected all wiring connections for obvious problems.
The third step was to perform the calibration that Toyota requires of the park/crash sensor system. During the calibration, it was failing when it got to the sensor in the passenger side mirror. We inspected the passenger mirror and connections for any obvious damage. Nothing obvious was found so we proceeded to replace the passenger side mirror with a known good part. After replacing the passenger side mirror, calibration would still fail when it got to the passenger side mirror.
Fourth step was to get a little deeper with the diagnostic process. Our Toyota mechanic printed off the factory wiring diagram relating to the passenger mirror, removed all trim panels needed to access wiring and began testing the wiring system. We found a broken wire in the harness going into the passenger side door. Mechanic was able to make a fairly simple wiring repair without having to replace the door harness.
Once the wiring was repaired, we were able to perform the Toyota calibration without any problems. Finished the repair up with a couple extended test drives to make sure there weren't any other concerns to show up. No other problems were found and all warning lights stayed off.
The key to properly diagnosing these more difficult problems is to keep an open mind. Early in my career as a mechanic, I would get over focused on the rear crash sensors due to that being the main area affected during the crash and when the warning lights came on. It is common sense to look into the rear of the vehicle first and assume the cause of the problem will be found related to the accident. In this case, the wiring problem found was not likely related to the crash at all. Now that I am almost thirty years into my auto repair career, I expect the unexpected. Most of the time, the clues given to you by the customer help point you in the right direction, but every once in a while, those clues can point you in the completely wrong direction.