4Runner Mirror Heating Issue

Mirror heating malfunctions can indeed be frustrating, particularly during colder months. Given that you've identified an error code related to the heating circuit and suspect a cable or connection issue, it is wise to proceed cautiously. Have you verified the integrity of the fuses associated with the mirror heating system? A blown fuse, although seemingly simple, is a common culprit. Furthermore, are you able to access the wiring harness that connects to the mirror itself? Inspecting the plug for corrosion or loose pins would be prudent.

I did check the fuses, and they all seem fine. I've also had a poke around the wiring harness where it connects to the mirror, but couldn't spot any obvious corrosion or loose pins. I'm starting to wonder if it could be the temperature sensor itself? Is there a way to test that, or is it more likely to be something further back in the system?

Given that you have already inspected the fuses and wiring harness, the temperature sensor is a plausible suspect. However, diagnosing electronic components without specialized equipment can be challenging. While it may be possible to test the sensor's resistance using a multimeter, interpreting the results accurately requires specific technical data. Considering the error code stored in the system, and the potential complexity of tracing the fault, I would advise consulting a qualified technician. A diagnostic assessment at a reputable workshop will likely prove more efficient in pinpointing the precise cause.

I think you're spot on – time to bite the bullet and take it to a workshop. Turns out it was the faulty connection as initially suspected. The mechanic located a corroded connector within the door harness and cleaned the connections. The repair including diagnostic cost me around 95€ I appreciate your input!