ABS engaging when it shouldn't
02-20-2015, 09:27 PM
#1
Senior Member
Thread Starter
ABS engaging when it shouldn't
I've noticed lately that when I apply my brakes the ABS will start to activate. This is during normal braking on dry pavement. Doesn't do it every time, but seems to be doing more and more. My fluid is clean and less then a year old. Pads have plenty of life left. I pulled each ABS sensor out and cleaned them, but the truck is still doing it. It's not terrible, but it's not right and isn't likely going to get better without some intervention. Any ideas on what would cause that? Truck is 06 with 5.4L and 4x2. I do have a front level kit and running 33 inch tires if that matters.
02-21-2015, 04:13 PM
#2
About 2 years ago, I installed a new bearing in my front passenger rotor on my '08 SCrew FX2 and ended up knicking the exciter ring in the process. It was enough to throw the magnetical field out of balance, and my ABS would pulsate no matter the speed when I applied my brakes. Needless to stay, I ended up replacing my front brakes after that. To temporarily fix the issue, I disconnected the ABS sensor on that wheel until I replaced the brakes the next weekend. It's possible that an exciter ring has become damaged, but you'd have to pull the front rotors off to tell. And the one in the rear differential is even worse to check, because you'd have to remove the cover to inspect it. I would think that a defective sensor would trigger a fault in the ABS system and cause the ABS light to illuminate, but anything is possible. You can measure voltage output on the sensors if you're up for the task.
Last edited by JByrd825; 02-21-2015 at 08:08 PM.
02-22-2015, 07:14 AM
#3
My girlfriends car was recently doing the same thing. We took it to a shop and all of the wheel speed sensors were reading different speeds (30-150mph) they said it was the abs module, we paid $40 from a salvage and hasn't done it since. It was a cavalier btw
02-22-2015, 09:12 AM
#4
Senior Member
Thread Starter
Thanks for the response guys. I'd like to check the sensors to see if they work. Checking the voltage is a good idea. I don't know what the specs are, but I would guess they should all be the same at least. I'll have to stick my head under there and see if there's a place to probe the wires and get a reading. Another question. You think it would be possible to remove the sensors and measure the resistance? That might be easier.
As for the ABS module, I'm really clueless as to what that even is. There's the block in front of the master cylinder that the hydraulic lines run through. Is that it, or is there an electronic module somewhere else that could potentially be going south? Thanks again for the suggestions.
As for the ABS module, I'm really clueless as to what that even is. There's the block in front of the master cylinder that the hydraulic lines run through. Is that it, or is there an electronic module somewhere else that could potentially be going south? Thanks again for the suggestions.
02-22-2015, 09:14 AM
#5
Thanks for the response guys. I'd like to check the sensors to see if they work. Checking the voltage is a good idea. I don't know what the specs are, but I would guess they should all be the same at least. I'll have to stick my head under there and see if there's a place to probe the wires and get a reading. Another question. You think it would be possible to remove the sensors and measure the resistance? That might be easier.
As for the ABS module, I'm really clueless as to what that even is. There's the block in front of the master cylinder that the hydraulic lines run through. Is that it, or is there an electronic module somewhere else that could potentially be going south? Thanks again for the suggestions.
As for the ABS module, I'm really clueless as to what that even is. There's the block in front of the master cylinder that the hydraulic lines run through. Is that it, or is there an electronic module somewhere else that could potentially be going south? Thanks again for the suggestions.
look in the lower drivers side corner of your engine bay..you will see a small pump with 5 brake lines coming out of it IIRC and a wiring harness
02-22-2015, 11:23 AM
#6
Thanks for the response guys. I'd like to check the sensors to see if they work. Checking the voltage is a good idea. I don't know what the specs are, but I would guess they should all be the same at least. I'll have to stick my head under there and see if there's a place to probe the wires and get a reading. Another question. You think it would be possible to remove the sensors and measure the resistance? That might be easier.
Last edited by JByrd825; 02-22-2015 at 11:54 AM.
02-22-2015, 01:22 PM
#7
Senior Member
Thread Starter
The ABS sensors work just like a stator. They produce voltage as the wheel spins. You can test them for resisatance, but their output is what you're really going to want to know. Disconnect the sensor and put a multimeter on it and spin the wheel at a steady pace. I forget what the threshold is for these things, but I'm sure a Google search would be beneficial.
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02-23-2015, 01:44 PM
#8
Not sure if it will help, but maybe try unplugging one abs sensor at a time. It might help you narrow witch sensor. But I'm not sure if it will work, it will also throw an abs code.
02-23-2015, 02:13 PM
#9
Senior Member
Are you actually feeling the ABS engage or are you getting pulsing like when ABS engages? If the latter then most likely you have a warped rotor. Your pads can look good and you could still be dragging one and overheating the rotor. These trucks are known for hanging brake pistons............. I actually had one of the 2 pistons in 1 caliper hang and it was giving me hellish feedback (like ABS way out of wack) when I stepped on the brakes. The amazing thing was I leveraged the caliper a little and it pushed the hung piston back just enough to release the pad, and the 2nd piston kept working so I was able to drive it the rest of the week and changed out the caliper over the weekend.