Code 4

Start vehicle and observe Yellow REAR ABS warning light for proper self-check. If Yellow light self-check is okay, go to next step. If Yellow light self-check is not okay, go to TEST A under PRELIMINARY CHECK TESTS .
Drive vehicle at 10 MPH on dry pavement. Depress brake pedal enough to lock all 4 wheels. After vehicle has stopped, place transmission in Park and release brake pedal. Wait 30 seconds. If Yellow light comes on, go to step 4). If Yellow light does not come on, go to next step.
Depress brake pedal hard and keep pressure on for 30 seconds while monitoring height of brake pedal. If brake pedal drops slowly, replace valve assembly. Go to CODE 16 under TEST DRIVE . If brake pedal does not drop, go to step 1) of this procedure.
Check for trouble codes. See RETRIEVING TROUBLE CODES . If Code 4 is present, turn ignition off and go to next step. If Code 16 is obtained, result is inconsistent. Repeat this step to verify Code 16 is received. If a different code is present, go to corresponding code under TROUBLE CODE DIAGNOSIS . If no codes are present, go to TEST D under PRELIMINARY CHECK TESTS .
Disconnect control module connector. Raise vehicle on hoist to allow wheels to spin freely. Ensure vehicle is in 2WD mode and hubs are unlocked. Start vehicle. Place transmission in Drive. Allow wheels to spin at idle for 30 seconds.
Apply brake with force of normal traffic stop. If rear wheels react slowly or continue to spin, replace valve assembly. Reconnect control module and go to CODE 16 under TEST DRIVE . If rear wheels react normally, reconnect control module and go to step 14) in CODE 4 under TROUBLE CODE DIAGNOSIS .

NOTE: Following test is designed to resolve a Code 5 condition. Performing test for any other reason may lead to incorrect diagnosis.