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Old 09-26-2018, 03:50 PM   #1
SCD
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ABS Low speed cutin

2001 1500 4x4 short bed step side Silverado.

I have a low speed cut in. Changed wheel sensors, no hub play, checked body ground. Checked air gaps and ohm readings all in specs. I don't get an abs light.

I don't have a scan tool.

Could the output shaft speed sensor on the trans make them cut in?

Broken wire?

Bad ABS computer?


Steve
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Old 09-26-2018, 05:55 PM   #2
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Re: ABS Low speed cutin

To eliminate guess work, you need to have it scanned for sensor inputs, there was a recall for this issue for sno belt registered trucks.
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Old 09-28-2018, 07:24 AM   #3
j cAT
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Re: ABS Low speed cutin

your comment on what is occurring is not clear to me.

So if you loose braking @5MPH the brake pedal pulses and the truck continues to keep moving then the sensors are not putting out the proper volts.

I have much experience with this I did the complete deal with this I even took apart the ECBM and did the repair work to the circuit board.

since NO codes and you have a scan tool that has the ability to read those GM ABS codes the wheel sensors must be removed and cleaned and if rust is inside the hub grease the hubs require replacing. the sensors are magnets so the rust will create the sensor volts to drop too low..

the hubs on the exterior rust so the rust will push out the sensor. then the gap between the encoder wheel in the hub is too far away and the sensor volts will drop.

the way to be sure whats up is , you have to disconnect the sensor use a volt meter set it to ac volts and spin the hub assy at a good speed by hand and see if the sensor volts is more than .3vollts AC.. the best reading should be .5volts AC or more. I have found if its .25volts AC or less this will cause your problem.

replacing the sensor is not proper as the sensor may require shims so it is at the proper gap ..if you clean these up and it still produces a lower volts then file the hub where the sensor is mounted then measure again .. if it gets up to .5volts that is the best reading .. .7 volts AC is also good ..

if your do require a new hub do the testing of the sensor volts before install !!!
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Old 10-01-2018, 08:13 PM   #4
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Re: ABS Low speed cutin

Thanks, your info fixed my problem. When installed the new sensors I checked the air gaps and they were in specs and the ohm readings were right.

When I checked the ac volts I miss read the specs. The readings I had were .05-.09 ac volts.

There were 2 shims under the old sensors and I installed them with the new ones, the air gaps were still in specs.

When I read your reply I noticed the volts were .5-.9, removed the shims and got the right voltage.

This was the strangest problem. No ABS light when slowing down from 30mph to 0. The ABS system would activate at 14mph with out braking to 5 mph and then deactivate.

After reading about Abs problems for week, I never found that reducing the air gap increases the voltage.


Thanks again for the reply.

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Old 10-05-2018, 10:42 AM   #5
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Re: ABS Low speed cutin

Well it is good you did fix it after you got / corrected the voltage output from the hub speed sensor..

back in the 1970's I began working on transportation vehicles that had a ABS system. so the sensors on the axles where adjustable and because they were not in a sealed area they got contaminated. the encoder wheel and the sensor collected iron dust that then caused the voltage to drop and the vehicle had to be brought into the repair facility..the operator had a switch that bypassed this ABS system so it could be operated at a higher speed to get back to the shop quickly..

this speed sensor stuff is magnetic so the greater the gap the less voltage.. and any rust in the hub will also drop the volts ..

greasing the hubs thru the sensor hole will reduce failures of the hub as this hub is not a sealed hub assy.. I just did a hub on a dodge challenger RWD.. hub was sealed. the speed sensor was outside of the hub but in a protected area. dodge called this encoder a sensor ring covered in a rubber material mounted on the axle .
never had any ABS issues with the dodge vehicles..

good luck and safe braking .....
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