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robert21
Active Member

United States
10 Posts
Posted - 03/18/2011 :  4:55:28 PM  Show Profile  Visit robert21's Homepage  Reply with Quote
Hello,
This 2004 GMC C-7 with CAT diesel engine, 4 wheel ABS is a rental truck, it came to us with both the red brake warning light and the amber ABS light on. We checked the usual, e brake and switch, fluid levels, fuses, power and grounds.
ABS scan codes:
1) U-1000 class II Data link Malfunction ABS data line

2) B0040 ABS R/Front speed sensor circuit malfunction

3) B0035 ABS L/Front speed sensor circuit malfunction

We checked the wires and connections at the ABS control unit and the wheel speed sensors, followed the harness from the left front wheel well to the right side, under the radiator, no visible chafing or damage. Tried wiggling the harnesses to see if any change - no. As mentioned in previous post, The ABS control unit is new. We even installed a 2nd new ABS controller, no change. Any body seen this kind of problem before?
Trying to avoid spending countless hours chasing this problem.
Thanks for your time.
Bob

tigger2
Advanced Member

USA
470 Posts
Posted - 03/21/2011 :  10:50:56 AM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
Pull the connectors from the abs module using the wiring diagram check the ohms of the wheel sensors from this end of the connector to see if you have continuity. Check carefully the wires where they enter the connector pull back the locks if they have them. I have found that someone probed the wires with a test light or piercing tool to check for voltage right at the edge of a wire under the lock cap, very hard to find small pin hole w/ green dust that used to be wire worked for a second and then quit. Test the twisted pair/J1939 for ohms should be 120 Ohms. Also try to push the front sensors against the tone ring and check for loose wheel bearings.
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busboy1988
Active Member

12 Posts
Posted - 03/25/2011 :  2:20:25 PM  Show Profile  Visit busboy1988's Homepage  Reply with Quote
check your original post-I put some thoughts there
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