battery checks out as 12.5V off / 14.4V running

 

Power supply is my first guess - alternator, battery, or poor connections.


How old is the battery?
Is it a Subaru alternator?
Connections tight and good and clean?

Ideally the battery is tested while incuring compelling issues - the lights may just be indicators that a problem recently existed rather than currently is happening - depending what you're seeing.

Ideally you clear all the codes, be prepared to read them immediately upon creeping up again, and see which one comes back first.

Any prior major engine or transmission work or accidents?

 

The ground cable to the abs/vdc module looks dirty


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@cardoc any suggestions? I know you did a write up on cleaning up and verifying grounds but i am having a tough time tracing them all.

 

Where did you get the speed sensors?

Did you clear the codes? If not, clear the ABS codes and start the car and move it to over 6 mph within a couple minutes of key on and start and see if the lights come back on. (and I do mean a couple minutes, no more that 4)

The codes are for the rear right speed sensor, front left speed sensor, steering angle sensor and the 500 is communications. All these run through the ABS/VDCCM.

To verify speed sensor feedback, you need a scanner that can communicate with the ABS or you have to do it manually with an ohm meter. A scan tool will show you if the speed data is sporadic or totally missing. If it's either, you would have to manually check the speed sensors and the harness to the ABS/VDCCM. Same with the SAS; a good scanner will let you see it's feedback.

Attached is the diagnostic tree. An ohm meter can be used in lieu of an oscilloscope.

You would have to jack the car up and check for play in the bearings. Any play in the bearings is a sign of damage and can throw off the speed sensor feedback. While it's up, you can remove the speed sensor at the suspect wheel and with a flashlight look at the reluctor ring while turning the hub to check for debris or excessive rust.

Given that there is 2 speed sensor codes with the SAS and the 500, I'm inclined to think that the problem is power related or the ABS/VDCCM is bad. Connection, grounds, condition of the pins in the bulk connectors, corrosion, and I/O function need to be looked at before throwing any more parts at it.

As for the grounds, there's 2 coming from the ABS and VDCCM. You found one. They both come out of the harness prior to the bulk connectors. The ABS connector has one, and the VDCCM has one. A connector diagram is attached also showing the pin designation.

If your main body ground from the battery is weak, that could be an issue. This will be the one from the battery to the fender. If this one is insufficient, then all the body grounds will suffer. If you have a good engine ground, then running a 6-10 gauge wire from the engine to the body would help, along with repairing the battery body ground if it's found to be bad.

I haven't had to replace any ABS/VDCCM modules on Gen 3s yet. It's always been an issue with a speed sensor or grounding. Hopefully your's will be the same type of result.

 

GREAT write up ! thanks so much. I need to carve out some time to diagnose this.

 

This eventually turned out to be damaged hubs. The drivers front and passenger rear were replace with NTN. The previous hubs were timkins.


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