Category: How Things Work

When wheel slip is noted while the brake is not applied, the ABS Computer-(EBCM) will enter traction control mode.

First, the EBCM requests the PCM to reduce the amount of torque to the drive wheels via the requested torque signal circuit. The PCM reduces torque to the drive wheels by retarding spark timing and turning off fuel injectors. The PCM reports the amount torque delivered to the drive wheels via the delivered torque signal circuit.


If the engine torque reduction does not eliminate drive wheel slip, the EBCM will actively apply the drive wheel brakes. During traction control braking, hydraulic pressure in each drive wheel circuit is controlled to prevent the drive wheels from slipping. The master cylinder isolation valve closes in order to isolate the master cylinder from the rest of the hydraulic system. The prime valve then opens in order to allow the pump to accumulate brake fluid in order to build hydraulic pressure for braking. The drive wheel inlet and outlet solenoid valves then open and close in order to perform the following functions:

Pressure Hold

Pressure Increase

Pressure Descrease

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    Comments (3)
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    • Guest - Kim Benfield

      My question is why the traction light is coming on my 2005 Chevy impala. What can be done to fix the problem. It doesn't do it all the time. It like it is grabbing and not want to move forward when applying the gas pedal.

    • Guest - Tech

      Soak it with WD-40 for awhile. May have to use a chisel and hammer to sort of break it loose. Tap a slot in the plug, then angle the chisel so when you tap on it you are trying to walk it around. It may just pop loose after a few taps. Worst case for this problem, you may have to heat it.

    • Guest - Jim

      I went to a quick change oil shop today to have my rear end grease changed on my 2000 Silverado. They were unable to remove the plug and rounded off the 3/8 plug hole. Any ideas would be be helpful. Thanks, Jim

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