The high level issue is power the rear defroster switch does not stay lit after pressing (it is lit when pressing). The result is the rear defrosted in not getting energized. I turned the car on, had someone hold down the rear defroster button, and I measured the voltage at the fuse (#25) with respect to ground – it is zero. For comparison, the fuse terminals at all other fuses had a voltage of 12-14 Volts. To ensure the dashboard button is not an issue, I removed the dash buttons/cover to expose the circuit board. I can simulate the defroster switch by simply touching the two circuit board terminal points with a piece of wire. Next, to further the analysis, I took power from another circuit and routed it to the fuse 25 socket that connects back to the rear defrost grid – this caused the defroster to operate (it melted snow). So bottom line, the defroster circuit FROM the TIPM is ok when power is applied. The failure point appears to be between dashboard circuit board to TIPM
Hello. Most of the time this is a problem with the TIPM> You would need a scan tool to see if there are any codes in the TIPM or to see if it is commanding the defroster to come on. Most of the time it is due to a code in the TIPM for a high amperage draw from the defroster which causes the TIPM to shut it down. This can be caused by a problem with the grid in the window or the TIPM programming. I have had to replace a few TIPM’s for similar issues as they do not properly take the programming. You would need to have a certified technician with the right scan tool that can scan this, like one from YourMechanic, that can come to you to [diagnose your defroster] https://www.yourmechanic.com/services/defroster-is-not-working-inspection
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