ABS activates when not needed


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Old 04-13-21, 03:23 PM
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ABS activates when not needed

I've read it's a somewhat common situation with older GM pickup trucks. Mine is a 2002 Silverado. When going very slow and applying the brakes, sometimes it feels like the ABS system activates. It's likely due to a defective sensor research shows.

For now would it be Ok/safe to remove the ABS fuse until I can get it repaired? I'm thinking not having ABS is safer than having the pedal occasionally almost going to the floor. I won't be driving it in slippery conditions.
 
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Old 04-13-21, 04:20 PM
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I would suspect pulling the fuse would be fine but you might take something else out in the process. You will have to test and see.

I had a 2000 Silverado that did the same thing. I fixed it by removing the ABS sensor, cleaning it off, and then cleaning the toothed "gear" inside with Q-tips. The sensor uses the "gear" to tell how fast the wheel is moving. I found my toothed gear had grease on it which was messing up the sensor. After cleaning it up it worked fine ever since.
 
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Old 04-13-21, 05:55 PM
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Yes I've heard the sensor getting dirty or rusty can cause that. Thanks for the Tips - pun intended. Your 2000 Silverado as you probably know is the same style/mechanical as mine. I believe pulling that fuse will also take out cruise control - not a concern. The truck is mostly used for hauling firewood and the occasional dump run, local home improvement store.

 
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Old 04-14-21, 05:38 AM
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I'm thinking not having ABS is safer than having the pedal occasionally almost going to the floor.
So ABS activation and long (soft) pedal have nothing to do with each other.

Most older trucks have simple 2 circuit ABS, front to rear. Long (soft) pedal is probably a bleed issue, air in the line!
 
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Old 04-14-21, 06:40 AM
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So ABS activation and long (soft) pedal have nothing to do with each other.

I was going to say the same thing. ABS activation doesn't produce the feel of your brake pedal going to the floor, rather almost as if it's being pushed back up. Something else is going on with the brakes.
 
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Old 04-14-21, 08:08 AM
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This is a common problem with steve's model truck. The fix is to remove the abs sensor from it's housing, clean the magnetic sensor eye on the sensor itself, and, clean the mounting surface for the sensor. You'll need to do both front sensors.
The cause is usually either the sensor eye getting covered, and, the sensor eye mounting surface becoming rusty and causing the sensor to sit crooked. The sensor could also have been mounted in cocked position and tightened.
While you're in there you might as well replace the brake pads since you'll have the rotor off.
Problem is called low speed ABS activation.
 
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Old 04-14-21, 12:33 PM
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I have a 2000 Suburban so basically the same vehicle. The sensor is corroded or just bad in one of the wheels. It can be replaced ($20 sensor/cable) but depending on how rusty things are, I suggest just unplug it or cut the sensor wire. No fuse needs to be touched. If the ABS brain sees a sensor missing, because you unplugged it, it shuts the ABS system down. Simple and much safer than a faulty activation.

- peter
 
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Old 04-14-21, 03:13 PM
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clean the magnetic sensor eye
There is no eye on the sensor, the magnetic tone ring produces alternating currents which the module reads to determine different wheel speeds, so there is no cleaning required.

99% of the time the sensor is bad or the wiring is compromised. I don know the cost of a new sensor but if only $20 then that is a cheap repair, and going by what the OP states, loads of wood, then having functional ABS is probably worth having!

 
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Old 04-14-21, 04:08 PM
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I wondered if it was something other than ABS activating, such as air in the lines. There are a lot of posts about this in Silverdo/Sierra forums, as mentioned 'Low speed ABS activation'. The defective sensor situation seems to be related to what I'm experiencing. I know ideally it would be repaired. I do hope for now I can disable the ABS system. If it was a daily driver or driven in slippery conditions, I wouldn't consider disabling the system. If I can find the sensor cable, I'd unplug it - but there are no lights to indicate a code to determine which wheel sensor could be causing the trouble.

The rear passenger side brake line was replaced in the fall of 2019. I don't think it happened for several months after that, so unlikely related. I did check the brake reservoir level, looked fine.

Maybe I should refer to the Anti-Lock Brake system - as I think that's what the system is trying to do. It would make sense that at very low speeds a sensor may not produce a signal (AC voltage from what I researched) which would be interpreted by the system as the wheel not turning, or locked up, skidding. The system would respond by releasing the brakes, allowing the wheel to turn again briefly? As mentioned you'd expect the brake pedal to be moved up, or out - but in vehicles when I experienced the system engaging when it should, as with a slippery surface I get the sensation of the pedal moving farther toward the floor. At the same time, braking force is reduced very briefly.

Thanks for the information.
 

Last edited by stevek66; 04-14-21 at 07:03 PM.
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Old 04-14-21, 07:02 PM
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You would know if it is the ABS kicking in. You should be able to hear it and feel it in the brake pedal.
 
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Old 04-15-21, 06:50 AM
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at very low speeds a sensor may not produce a signal
Its not that is doesn't produce a signal it's that the module detects a difference in signals between all he other sensors.

As you turn, one wheel is turning faster than the other, low tire pressure will turn at different speeds than the other.

When you get out of "specifications" is when ABS engages.

If you have a bad sensor, or a frayed wire, or a connector with corrosion that can cause voltage drops that the module reads as slip and the module to activate!

 
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Old 04-15-21, 12:34 PM
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you don't have to know which sensor if you want to deactivate the ABS system. Disconnecting any of the sensors shuts the system down and you will get an ABS light on your dash. do a test run with it connected and without to see the difference. A little speed on some dirt or gravel will engage it. Earlier comment about keeping the ABS functional is true if you tow or haul loads. otherwise, if it is a simple daily driver, leave it disconnected.

- Peter
 
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Old 04-16-21, 12:38 PM
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Ideally I'd get it fixed and will when I can. I know it's not a good idea to disable ABS. If it was disconnected temporarily, I wouldn't have expected needing to avoid driving it in April. This morning I had about 2 inches of snow on the ground and it was coming down pretty good. I'm fortunate to have a company van, so the truck is used very occasionally.

Good tip re: disconnecting one of the sensors. I had no idea what that would do, but I see it should disable the whole system. There's no ABS light now so eliminating one wheel at a time would be the way to isolate it. Since there's no ABS light I assume there would be no codes, but someone mentioned to me there still may be.
 
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Old 04-17-21, 10:22 AM
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For now I pulled the 60A fuse in the compartment under the hood. There's another ABS fuse in the compartment by the dashboard. Of course ABS and Brake are now lit on the dash, but the brakes feel fine. Tried to make the situation happen, but couldn't. I feel this is safer as my street has a slight decline to the main road where there's a stop sign. Several times while braking on that decline the ABS would activate and I rolled forward. Same would sometimes happen when entering my driveway, which is also at a slight decline.

The truck passed emissions about a year ago so not due for another year. I believe it would fail and not be eligible to be tested with those dash lights on even though it's not emissions related.
 
 

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