Antilock Braking System (ABS)

Part 1 Of 2:

Part 2 Of 2:

CIRCUIT DESCRIPTION
The toothed wheel generates a voltage pulse as it moves past the sensor. Each tooth-gap-tooth series on the wheel generates a pulse. The EBTCM uses the frequency of these pulses to determine the wheel speed. The amplitude of the voltage generated in each pulse depends on the air gap between the sensor and the toothed wheel and depends on wheel speed.

CONDITIONS FOR SETTING THE DTC
- Damaged or missing teeth on one or more of the wheel speed sensor rings.
- Noise on one or more of the wheel speed sensor signals.
- The EBTCM cannot specifically identify which wheel speed sensor is causing the malfunction. If the EBTCM can define the specific speed sensor causing the malfunction, the DTC associated with the sensor (DTC 39, 42, 44, or 46) will be set concurrent with or instead of DTC 25.

ACTION TAKEN WHEN THE DTC SETS
- A malfunction DTC is stored.
- The ABS and the TC indicator lamps are turned on.
- The ABS and the TCS are disabled.

CONDITIONS FOR CLEARING THE DTC
- The condition for the DTC is no longer present.
- The scan tool Clear DTCs function is used.
- 100 drive cycles have passed with no DTCs detected.

DIAGNOSTIC AIDS
Check the toothed wheel for any large grooves, gouges, marks, etc. that might influence the tooth's signal at the wheel speed sensor. Also check for a buildup of foreign material in the gaps between teeth in the toothed wheel, as the material may cause this malfunction.
A worn hub/bearing assembly may cause this fault in extreme cases. The bearing play allows the sensor-to-toothed-ring gap to change excessively.

TEST DESCRIPTION
The number(s) below refer to the step numbers on the diagnostic table.
2. If DTC 39, 42, 44 or 46 is set current or history, the DTC set is likely the sensor that has set DTC 25.
4. This step checks if the spark plug wires and wheel speed sensor wiring are in close proximity to each other.
5. If the scan tool can record any erroneous wheel speed signal, diagnose those sensors first.