Testing Procedures & Precautions

CAUTION: Before raising vehicle, turn air suspension switch off. See Figure . Failure to turn off switch could damage air suspension.

Testing should be done in the following sequence: ON-BOARD SELF-TEST TROUBLE CODE INDEX , ABS QUICK CHECK CHART (Figure ), WARNING LIGHT SYMPTOM SEQUENCE DIAGNOSTIC CHART (Figure ), and CIRCUIT TESTS. If Super Star II tester is not available, ON-BOARD SELF-TEST TROUBLE CODE INDEX table may be by-passed.

Failure to test system in sequence will result in misdiagnosis of ABS and unnecessary replacement of components. ECM cannot store trouble codes with same first digit (25 and 26). Lowest number code (25) will be stored first. First codes must be serviced, cleared and reset (drive vehicle over 25 MPH).

Solenoid valve service codes will override all other codes stored. If no codes are stored, system has passed self-test. If code appears, refer to ON-BOARD SELF-TEST TROUBLE CODE INDEX . If BRAKE warning light is on or intermittently comes on, use WARNING LIGHT SYMPTOM SEQUENCE DIAGNOSTIC CHART. See Figure .

Before beginning tests, release parking brake. Verify brake fluid level is correct. Check that all anti-lock brake electrical connectors are properly connected. Check that battery cables are clean and tight.

NOTE: There are 2 ways of testing ABS system: quick check or system check.