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Hey all. I have a 2000 Silverado with ABS issue. Previous owner disconnected the wheel speed sensor and pulled the fuse. Replaced ABS sensor and fuse, reset codes and drove the vehicle for a good bit. ABS kicks in intermittently. He have a bi-directional scan tool but the truck doesn’t give many options for ABS besides a few basic active tests and live data to front two wheels and one back wheel.
where would you start diagnosing? No DTC besides the front wheel speed sensor code, which has been replaced. no history codes previous to front left ABS code.
When you say the ABS kicks, you mean you're getting unwanted ABS activation? As in, the ABS is running when it's not needed.
My first thought is excessive sensor air gap or worn wheel bearing. You can normally see this issue easily enough with a scan tool. Find yourself a wide open parking lot and use it to roll forward very slowly (straight ahead) while watching both front wheel speed sensor signals.
These sensors show 3 MPH at a stop, all the way up to 3 MPH. After that, they indicate normally. I suspect what you'll find is one sensor will start reading noticeably sooner than the other. While rolling forward, the right front might show 6 MPH while the left front shows 3 MPH, for example. The ABS system will interpret that as a locking left front wheel and run the ABS.
You may need to keep the vehicle speed in the 4-7 MPH range in order to catch the problem, especially if your scan tool doesn't graph data.
Yes, all sensors indicate 3MPH at a stop. I will see if they match the speedometer. Correct, I get unwanted ABS. Almost like I slammed on the brakes. Pump starts going and the pedal gets tough. I haven’t really looked at closely yet, I just parked it and posted this thread. I’m going to inspect the ABS module wiring as well, this truck has been an absolute mess both mechanically and electrically from the previous owner(s). No real history on it.
I agree with Tyler, this is almost always the result of a failing wheel hub. It doesn't need to make noise or have a bunch of play, once you ID the sensor dropping out, changing that wheel hub with the sensor will fix it. Changing the sensor alone isn't enough, they always get a new wheel hub when I see this.
So, coming back to this. What i've done so far is check for play in both front wheel bearings. Zero play. Replaced LF ABS sensor. due to previous owner cutting it off. I notice a new axle and new ball joints on that side. Took RF apart yesterday and tested ABS sensor per the shop manual, 1 rev per second and 350mv ac at least. Didn't get anywhere near that. Also, i noticed each hub has a different tone ring in it. When turning left (have not tried right yet), ABS pump and all kicks on and when watching wheel speed, both front wheels cut out while the rear keeps reading.
Ideas? I see that part 15946732 seems to be the revised and replacement hub, but i don't want to start throwing parts at the problem without a solid conclusion.
When these come in with the symptoms you describe, I graph the wheel speed sensors on the scan tool and change the bearing for whichever one looks irregular.
Most of the time the bearings are not loose or loud.
The only exception (speaking about GM vehicles) is if when cutting the wheel all the way one way or the other while the vehicle is stationary, if the abs warning lamps come on then usually I find a broken wire in the harness where it's clipped to the control arm. I only see that on older GM sedans. Impala, Grand Prix, Lacrosse etc.
Yes! I am familiar with the GM internal conductor issue in the harness, which is what i checked for initially. IIRC there was a TSB for the N bodies about that issue.
In the end, i ended up getting two wheel hubs ordered to:
A ) Get the tone rings the same
B ) Eliminate the hubs since i don't know the history of the vehicle
C ) Eliminate the WSS because one tested way out of spec and the other was new but since the hub comes with sensors, I will return it
Thanks for the help guys. Ultimately I was on the right track and just wanted a secondary opinion from the fine folks here!
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