Diagnostic Aids

Intermittent condition can be caused by a poor connection, rubbed through insulation or a wire that is broken inside the insulation. The frequency of the malfunction can be checked by using the enhanced diagnostic function of the TECH-1 scan tester as described in the tester manual.

Any circuitry that is suspected of causing an intermittent complaint should be thoroughly inspected for backed out terminals, improper mating, broken connector locks, improperly formed or damaged terminals, poor terminal-to-wire connections or physical damage to the wiring harness.

If driver's complaint reflects that ABS indicator is only on during moist conditions (rain, snow, wash, etc.), all wheel speed sensor circuitry should be inspected for signs of water intrusion. This can be verified by spraying down suspected areas with a 5 percent salt water solution (2 teaspoons of salt in 12 Ozs. of water). Start vehicle and allow to run for 10 seconds. If code returns immediately, replace suspected/tester harness.

Fig 1: DTC A027 Schematic, Left Rear Excessive Wheel Speed Variation

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC A027 Flow Chart (1 Of 3), Left Rear Excessive Wheel Speed Variation

Courtesy of GENERAL MOTORS CORP.

Fig 3: DTC A027 Flow Chart (2 Of 3), Left Rear Excessive Wheel Speed Variation

Courtesy of GENERAL MOTORS CORP.

Fig 4: DTC A027 Flow Chart (3 Of 3), Left Rear Excessive Wheel Speed Variation

Courtesy of GENERAL MOTORS CORP.