ABS Troubleshooting
 

ABS went out which made for an interesting day at the track yesterday. ABS light is on and front left tire locks up at 50% braking. I've bled the front brakes to try and get it braking more evenly and have pulled the wheel sensors and cleaned them to make sure that wasn't the issue.

Any recommendations on next steps to troubleshoot?

Read the error codes using Durametric?

No fault codes.

No ABS controller fault codes? I assume Durametric is capable of querying the ABS control module for these?

If possible you might try swapping wheel speed sensors from side to side to see if the problem follows the sensor of course.

Absent a mecnhanical problem: a pinched brake line to that locking wheel; a bad wheel speed sensor; the ABS control module has to be suspect.

Is Durametric capable of performing a system/functional check out of the ABS module? If so this would be a good next step. If not then one needs access to a Porsche diagnostics computer.

Possibly a bad wheel bearing?

Yes, Durametric communicates with the ABS module.

Dumb question: Wheel spins freely when the car's off the ground?

I'd...hm. Use Durametric activations to try to activate the ABS pump and see if it's actually functional.

Check the brake pedal switch - potentially cheap solution to a potentially expensive issue.

Aside from what has been mentioned, make sure all your brake lights are working. I've heard of some problems with the ABS/PSM system when the brake lights are not working correctly.

Ok, I'll take a look this afternoon. Durametric has an ABS/PSM 5.3 module that appears to be communicating. That's where I checked for the ABS Fault Codes.

This is almost identical to my first time with this car on track when I had the ABS sensor and the pad wear plugs reversed. Luckily this time I didn't brake the subframe when I went off track. I'll try swapping the sensors around first.

Wheels sensors swapped out with DD, no luck. Wheels turn fine.

Ahsai, my gut is it's a wiring issue. Any tips on how to troubleshoot it?

I would go to the module that each wheel sensor is wired to, place car on jacks and check the output of the wheel sensor at the module, should get about 1 volt AC when rotating the wheels, you will need a wiring diagram to know which wires are to each sensor, if you find one that does not put out, go to the connector at the wheel and check output there, if none, change the sensor, if snesor is ok , do a continuity check of the harness back to the module.

Ahhh, that makes sense. I was looking for DC voltage off the wheel sensors. OK, that gets me going back in the right direction.

Continuity to wheel well sensors is good. Voltage from sensors is good. Going to order a salvage ABS unit but hopeful somebody has more ideas on things to check.

Did you work on the ABS system before such as disconnecting the sockets, sensors, etc?

The sensors have been unplugged a few times but never taken out of the wheel. Nothing else has been touched. One thing that did happen is the headlight harness came loose and got chewed up by the wheel. So I unplugged and pulled the harnesses for both sides. Seems like that was the same day but I can't remember for sure.

Dammit. Replacing the ABS controller didn't fix it. I'll try the brake switch but the brake lights are working just fine. Any other ideas? Last two track days of the year are this weekend.