DTC 25

Fig. 114 Code 25: Front Left Wheel Speed Sensor Fault (Part 1 Of 2).:

Fig. 114 Code 25: Left Front Wheel Speed Sensor Fault (Part 1 Of 2).:

DTC 25: Left Front Wheel Speed Sensor Fault:

CIRCUIT DESCRIPTION:
As each wheel turns, the wheel speed sensor for that wheel creates a small AC voltage as a toothed sensor ring, mounted in the front integral hub/bearing assembly, is passed by the stationary sensor. The sensor consists of a permanent magnet and coil and generates voltage by magnetic induction. The frequency of the wheel speed sensor signal is proportional to wheel speed.

The EBTCM/EBCM uses the wheel speed sensor signal to calculate vehicle reference speeds and individual speed, acceleration and slip values for each wheel. These values are used to determine when antilock control is required.

The EBTCM/EBCM will only set one wheel speed sensor fault code at a time, even if multiple faults exist. Detection is prioritized accordingly: LF, RR, LR, RF Always check for additional stored codes after making repairs.

TEST CONDITION(S)
1. Tested continuously.

FAILURE CONDITION(S)
Sensor Output
1. Drive-away: Speed signal is not detected when vehicle reaches 12 km/h or 7.5 mph.
OR
2. While Driving: Speed signal is lost while vehicle speed is greater than 40 km/h or 25 mph

ACTION TAKEN
1. Code set.
2. ABS/TCS switched "OFF."
3. "ANTILOCK" indicator "ON."
4. "TRACTION DISABLED" message displayed. (vehicles with TCS)

Code 25 is set if there is a short to voltage or ground in CKT 830 or 873, or faulty speed sensor. The testing for this fault occurs when vehicle is in motion; it will not set with the ignition 'ON' and the vehicle at rest.

NOTICE: A Code 25 may set if CKT 830 or 873 lose continuity and the WSS signal is lost while driving. A Code 27 should accompany this code on the subsequent ignition cycle. If both Code 25 and Code 27 are set concurrently, diagnose Code 27 first.

TEST DESCRIPTION
Test numbers refer to circled numbers on the diagnostic chart.
1. Checks if the code resets during a road test.
2. Use the TECH 1 to check for sources of induced electrical noise. Some sources of induced electrical noise which may cause intermittent wheel speed sensor codes to set are: improper routing or sensor cables next to spark plug wires; cables not retained in brackets; loose fitting or improperly mounted sensors; damaged sensors or toothed rings; poor terminal engagement of connectors; or intermittent shorts or opens in wiring; or a loss of sensor circuit shield.
3. Checks for damaged wheel speed sensor circuit shield. The shield is a foil insulator that is wrapped around the wheel speed sensor circuits. Inside the EBTCM/EBCM harness connector, there is an uninsulated drain wire that is attached to the shield and jumped to the wheel seed sensor return line and taken to ground through the EBTCM/EBCM. A shield which has lost its ground through the EBTCM/EBCM leaves the sensor signal circuit susceptible to noise. It may be necessary to disassemble the EBTCM/EBCM connector to check if the drain wire has a poor connection with the wheel speed sensor return connector terminal. The shield can be repaired by reterminating the sensor return line circuit, including the drain wire.
4. Checks for intermittent opens/shorts in wheel speed sensor circuits and cables.
5. Checks for proper resistance in the sensor itself.
6. Checks for a short to battery in either of the speed sensor circuit wires.
7. Checks for a short between the speed sensor circuit wires.
8. Checks for a short to ground in the speed sensor input circuit wire. The ground may be either a 'hard' short to ground, or a resistive short. A short with a resistance less than 2 megohms, though not a hard short, can still cause Code 21 to set.
9. Checks wiring and connectors for intermittents.