Parking brake not working - 2017 Model X

[Retkimora]

Hello,

My Model X gave me some headscratching few weekends ago. Entered the car and got notified immediately about parking brake not releasing or being applied. I tried to switch between P and D many times and could hear only rear left side engaging. Right side was completely quiet. Car would move but rear right wheel would drag without turning.

I jacked the car up and removed wheel. This model has only one brake caliper and parking brake motor/mechanism in it. Motor is held on to the caliper with two 5mm allen screws. Connector has red locking plastic clip. After removing the motor I stuffed in 7mm flat head screw bit in place where motor gear would go and undid the parking brake. Now I could move the rear wheel freely by hand. Problem partly solved, I could drive again. Put motor, connector and wheel back on. Car would drive but complain about parking brake failure. Autopilot is not available when this error is on. Actually you can see visualization all the time and car will alert you about collision warnings. But whenever you touch autopilot stalk all the visualizations and collision warnings will be gone. They seem to come back at some point. Doesn't matter me too much.

Later I took the motor off again and applied 12V to its terminals. To my surprise the motor ran fine. Swapping 12V changed motor direction. I measured the car side of the motor connector and it gives something between 4-5VDC all the time. Searched service.tesla.com for wiring schematics and found that two wires go directly to some park brake controller. I measured those same wires at controller end when park brake motor was connected. Same 4-5V all the time, no matter if car was on P or D. I also measured healthy side: voltage was sitting at 0V when motor was not in use and got 12V whenever it was asked to operate.

Tried rebooting the car many times and even software reinstall. Didn't work.

I suspect the park brake controller is shot. I ordered second hand part for 50€. Currently waiting for the part to arrive.

 

[brainhouston]

Great troubleshooting, looks like u nailed it
If u want to be extra thorough, u could swap left/right motors (assuming they're same) to be 101% sure

 

[Retkimora]

I got the spare parking brake box and it didn't work any better after software update. Then I realized I had forgotten to measure those two wires going to motor. Took the connector off the motor and measured both wires all the way to the electronic box. Another wire was fine and other had resistance of like 500kOhms. Took wire from motor away from its covering sleeve and cut zip ties holding it to clips. At one clip zip tie was really tight and the problem was really obvious after seeing whats under the zip tie. Wire broke in two when I touched it.

Fix was relatively easy. Stripped wire ends, cleaned copper strands and soldered them together. Heatshrink on and back to its protective sleeve. After getting everything back together I had to switch between N and D couple of times until I heard the motor struggling to push piston any further. At the same time all the error messages disappeared.

Maybe the box was waiting to see some (lower than 500kOhm) resistance until it sends full 12V to the wires. Who knows. I am happy it is working again.