ABS kicks in at slow speed
Posted: Tue Jun 12, 2007 9:10 am
This is a compilation of my posts from the other board in response to a problem that Tripplec was having. Most all of us with affected year vans will likely see this problem. Feel free to fill in the rest of the post if you guys want. I just thought it should be archived in case the database on the other board goes bye, bye, as it is a serious safety concern. I also added the test and repair procedure and specs as I originally sent a copy of the TSB to Tripplec and didn't have time to get to posting it before the board went down. You may wish to do the repair procedure even if you aren't having problems as a preventive measure.
This affects '95-'03 Astro/Safari
GM has recalled a whole bunch of trucks for this problem. My dad was having problems with his 2000 Silverado 1500. I test drove it for two days, then litterally came within 1 inch of hitting the car in front of me at a gas station, thank god for parking brakes. If you pull the ABS fuse you can safely drive the van, had to do this to his truck until GM officially recalled it, they said there was a recall coming in a couple of weeks, it had started in other regions of the U.S. It was 2 months later. I don't think that they have a recall on the Astro/Safari but give GM customer service a call and raise hell, I bet they fix it for you. If not, I recommend replacing the sensor as the plastic deforms. The hole it is in gets rusty and "puts the squeeze on" the sensor. If it was my vehicle I would replace the whole assembly as you are for sure going to get the hub full of rust and dirt when you clean the mounting hole with a wire brush (use one like you would use for cleaning copper plumbing fittings before soldering).
The system won't set a code because it sees a sensor that is dropping rate and thinks that the wheel is locking up. I know what you mean about the pedal effort when it occurs. I could squat over 400lbs in high school, and while that was a while ago, my legs are still quite big, and there was no way I was stopping that silverado with the service brake. Got out, gassed up and pulled the fuse. It usually starts out very intermittent. Had to drive dads for 2 days before it tried to kill me. Ok so the speed is low when it happens. Since I have seen 3 or 4 more and sent all but one to dealers under warranty. The sensors are held in by one bolt, due to the rust they can be a pain to pull out though. I can see if I can find the revised resistance and voltage specs for the sensors, I don't know if I still have the TSB around and I had to get it from a dealer. I'm going to the dealer tomorrow morning for parts... If I remember right you may be able to spin the wheels while measuring the voltage and the lower voltage one is most likely the culprit, but both may be bad. If just one is bad, the other isn't far behind most likely.
You don't need to turn the tires very fast at all to see the voltage reading. The spec is for just turning them by hand. I seem to remember finding them just by the resistance measurement also.
1. Disconnect front wheel speed sensors
2. Rotate wheel by hand and measure AC mV across sensor.
Reading should be at least 350 mV AC
3. If reading is between 200 and 350 mV AC
Remove speed sensor and plug hole
Clean sensor mounting surface thoroughly
Check sensor for warping/distortion/cracks and check the head for flatness
Spray 2 thin coats of GM 89022217 (89022218 Canada) rust penetrating lube
When dry apply thin coat GM 01051344 (993037 Canada) bearing grease to hub surface and sensor o-ring
Install sensor, or new sensor if necessary
Recheck voltage reading
Hope this helps someone.
This affects '95-'03 Astro/Safari
GM has recalled a whole bunch of trucks for this problem. My dad was having problems with his 2000 Silverado 1500. I test drove it for two days, then litterally came within 1 inch of hitting the car in front of me at a gas station, thank god for parking brakes. If you pull the ABS fuse you can safely drive the van, had to do this to his truck until GM officially recalled it, they said there was a recall coming in a couple of weeks, it had started in other regions of the U.S. It was 2 months later. I don't think that they have a recall on the Astro/Safari but give GM customer service a call and raise hell, I bet they fix it for you. If not, I recommend replacing the sensor as the plastic deforms. The hole it is in gets rusty and "puts the squeeze on" the sensor. If it was my vehicle I would replace the whole assembly as you are for sure going to get the hub full of rust and dirt when you clean the mounting hole with a wire brush (use one like you would use for cleaning copper plumbing fittings before soldering).
The system won't set a code because it sees a sensor that is dropping rate and thinks that the wheel is locking up. I know what you mean about the pedal effort when it occurs. I could squat over 400lbs in high school, and while that was a while ago, my legs are still quite big, and there was no way I was stopping that silverado with the service brake. Got out, gassed up and pulled the fuse. It usually starts out very intermittent. Had to drive dads for 2 days before it tried to kill me. Ok so the speed is low when it happens. Since I have seen 3 or 4 more and sent all but one to dealers under warranty. The sensors are held in by one bolt, due to the rust they can be a pain to pull out though. I can see if I can find the revised resistance and voltage specs for the sensors, I don't know if I still have the TSB around and I had to get it from a dealer. I'm going to the dealer tomorrow morning for parts... If I remember right you may be able to spin the wheels while measuring the voltage and the lower voltage one is most likely the culprit, but both may be bad. If just one is bad, the other isn't far behind most likely.
You don't need to turn the tires very fast at all to see the voltage reading. The spec is for just turning them by hand. I seem to remember finding them just by the resistance measurement also.
1. Disconnect front wheel speed sensors
2. Rotate wheel by hand and measure AC mV across sensor.
Reading should be at least 350 mV AC
3. If reading is between 200 and 350 mV AC
Remove speed sensor and plug hole
Clean sensor mounting surface thoroughly
Check sensor for warping/distortion/cracks and check the head for flatness
Spray 2 thin coats of GM 89022217 (89022218 Canada) rust penetrating lube
When dry apply thin coat GM 01051344 (993037 Canada) bearing grease to hub surface and sensor o-ring
Install sensor, or new sensor if necessary
Recheck voltage reading
Hope this helps someone.