ABS, brake light, turn indicator issue

[ChrisPerry]

My ABS light and the brake warning light flash randomly back and forth. When my lights are on and I touch the brake the tail and running lights dim. Turn indicators turn on, but dash lights turn off.

No codes stored. At least none that my programmer or cheap scanner will pull. (Will scan with snap on scanner Monday.

So far I've checked....

Both batteries and connections
Ground under cab on frame
Ground under ds battery on frame
all bulbs in tail light assemblies
all marker light bulbs

I'll check ignition swich voltage next. If it's ok, is there anything else it could be other than the ABS control computer? How can I test the ABS computer?

Any help is appreciated.

 

[ChrisPerry]

Pulled the codes with a Snap-on scanner today

P0571....... brake switch
U1000...... manufacturer controlled DTC
U1041...... loss of communication EBCM
C0281...... brake switch circuit
C0238...... wheel speed sensor mismatch

Acording to the scanner, 3 speed sensors read 3mph and 1 reads 0mph at a stop.
ABS voltage says 0.0 (again, according to the scanner)

I plan on breaking out the multimeter tomorrow and verifying voltage and grounds at the EBCM harness plugs.

Any other suggestions would be helpful.

 

[duramax on fire]

Sounds like your losing a ground somewhere. Are you just inspecting the grounds visually or using an omh reading to verify the cable isn't broke inside.

 

[ChrisPerry]

I pulled the grounds sanded the teminals and the frame and rebolted them. For peace of mind, tonight I probed the grounds a foot from the terminals, with the positive clamped to the battery. 12.45 volts, same as dirrectly at the battery.

Came inside about 20 min ago to find a wiring diagram, when I went outside it's working perfectly.

This needs to stay broken until I figure out what's wrong. Guess I'll go for a drive and see if I can get it to act up again....

 

[ChrisPerry]

Well finally got this fixed, hopefully. Figured I'd update the thread incase someone else runs into this issue.

Pulled abs fuse and drove over a month without any issues. Reinstalled fuse and issues started up immediately. Pulled fuse again, all's well a few days until I pull the fuse again and within 50 ft all's screwy again.

Replaced abs module tonight and after 45 min of driving around still no issues. :woott: