Code 4

Start vehicle and observe Yellow 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 - YELLOW LIGHT OFF, DOES NOT SELF-CHECK under PRECHECK 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 11) in CODE 4 - OPEN OR GROUNDED VALVE RESET SWITCH under TROUBLE CODE DIAGNOSIS .
Check for trouble codes. See RETRIEVING TROUBLE CODES . If Code 4 is present, replace valve assembly. Go to CODE 16 under TEST DRIVE . 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 - YELLOW LIGHT CHECK OKAY, BUT DOESN'T FLASH TROUBLE CODE under PRECHECK 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. Go to step 11) in CODE 4 - OPEN OR GROUNDED VALVE RESET SWITCH 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.