ABS Failure

[JayG99]

During an autocross yesterday, my ABS went out and the OBD says ABS FAILURE and the ABS idiot light is on. I have only basic ABS, no PSM
Brakes work fine, just no ABS. 
 
I have a new found appreciation for ABS. Without it working, its really easy to lock up the brakes.
 
In searching, it could be a wheel sensor that went bad. I did find some info on testing them with a OHM meter, but there were several values mentioned and I don't know what the correct one is.
 
Anyone have any thoughts on troubleshooting the problem?

[JFP in PA]

Year and model of the car, and what codes?

[JayG99]

2004 986 S 

codes 4210 & P0501

Thanks

[JFP in PA]

4 hours ago, JayG99 said:

2004 986 S 

codes 4210 & P0501

Thanks

 

I'm away from the shop at the moment, so working from memeory P0501 is for no speed signal, which can come from multiple sources:

 

Break or short in the wiring from the ABS module to the ECM

Break in the wiring from the left rear wheel speed sensor to the ABS module

Left rear wheel speed sensor is dead.

Pull the left rear wheel and check for a damaged sensor or heavy build up of brake dust.  If OK, check the speed sensor for resistance, should be 1.6-1.8K ohms.

[Loren]

JFP is correct on P0501.

 

P4210 Rear right speed sensor

- open circuit short to ground/short to B+

[JayG99]

Yup!

Swapped out one from my 996 and the ABS system works properly. Bad right rear sensor

it read .4k and the good one 1.8k

 

Cleared the codes and will see if the P0501 comes back

 

Edited July 3, 2017 by JayG99

[JFP in PA]

3 hours ago, Loren said:

JFP is correct on P0501.

 

P4210 Rear right speed sensor

- open circuit short to ground/short to B+

 

For future readers of this thread, watch which year you are looking at as Porsche reversed codes on the later DME, making P0501 the right sensor on cars with a 7.8 DME, which the OP has:

 

[Loren]

Just one more reason why Porsche diagnostic compatible scanner/tool makes a world of difference.