GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC C0035 00: Left Front Wheel Speed Sensor Circuit

DTC C0035 5A: Left Front Wheel Speed Sensor Circuit Erratic Signal

DTC C0040 00: Right Front Wheel Speed Sensor Circuit

DTC C0040 5A: Right Front Wheel Speed Sensor Circuit Erratic Signal

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Left Front Sensor Signal Circuit

C0035 00

C0035 00

--

C0035 5A

Left Front Sensor Low Reference Circuit

C0035 00

C0035 00

C0035 00

C0035 5A

Right Front Sensor Signal Circuit

C0040 00

C0040 00

--

C0040 5A

Right Front Sensor Low Reference Circuit

C0040 00

C0040 00

C0040 00

C0040 5A

Circuit/System Description

The wheel speed sensor receives ignition voltage from the electronic brake control module (EBCM) and provides a DC square wave signal back to the module. As the wheel spins, the EBCM uses the frequency of the square wave signal to calculate the wheel speed.

Conditions for Running the DTC

C0035 00 or C0040 00

    • The ignition is ON.
    • Ignition voltage is greater than 9.5 volts.

C0035 5A or C0040 5A

    • The ignition is ON.
    • Ignition voltage is greater than 9.5 volts.
    • The brake pedal is not pressed.
    • A DTC is not set for the other wheel speed circuit on the same axle.

Conditions for Setting the DTC

    • An erratic signal output of the wheel speed sensor is detected.
    • A short to ground, open/high resistance is detected on the wheel speed sensor signal circuit.
    • A short to voltage, short to ground or an open/high resistance is detected on the low reference circuit.
    • Wheel speed sensor power supply is less than 7.6 volts.
    • A missing wheel speed sensor signal

Action Taken When the DTC Sets

    • The EBCM disables the Antilock Brake System (ABS)/Traction Control System (TCS) and VSES for the duration of the ignition cycle.
    • The electronic brake distribution (EBD) does not function optimally.
    • The ABS indicator illuminates.
    • The Traction Control indicator illuminates.
    • The driver information center (DIC) displays the Service Stability System message.

Conditions for Clearing the DTC

    • The condition for setting the DTC is no longer present.
    • The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
        The condition for setting the DTC is no longer present.
    • An ECE 13 response may be required, after repairs are made, and DTCs are cleared, operate the vehicle at speeds greater than 15 km/h (10 mph) to complete the self test, and the EBCM will turn off the ABS indicator

Diagnostic Aids

    • Inspect the back of the wheel bearing on the encoder surface for metal debris that could cause an erratic reading with the sensor. Do not use a magnet to clean the debris, or damage to the encoder ring may occur.
    • If 2 or more wheel speed sensors are inoperative diagnose each wheel speed sensor individually.
    • If the customer comments that the ABS indicator is ON only during moist environmental conditions: rain, snow, vehicle wash, etc., inspect the wheel speed sensor wiring for signs of water intrusion. If the DTC is not current, clear all DTCs and simulate the effects of water intrusion by using the following procedure:
  1. Spray the suspected area with a 5 percent saltwater solution. To create a 5 percent saltwater solution, add 2 teaspoons of salt to 8 fl oz of water (10 g of salt to 200 ml of water).
  2. Test drive the vehicle over various road surfaces: bumps, turns, etc., above 40 km/h (25 mph) for at least 30 seconds.
  3. Rinse the area thoroughly when completed.

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Antilock Brake System Connector End Views

Description and Operation

ABS Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Verification

Ignition ON, observe the scan tool Wheel Speed Sensor parameter . The reading should be the same speed on all sensors when driving in a straight line at a speed greater than 20 km/h (13 mph).

Circuit/System Testing

Important: It is recommended that Component Testing is performed before Circuit Testing when diagnosing wheel speed sensors because the module will default and does not supply voltage to the sensor when the DTC is set.

Performing Circuit Testing with EBCM connector disconnected and key on will cause U codes to set. Clear DTCs after performing the test.

  1. Ignition OFF, disconnect the harness connector at the EBCM.
  2. Ignition ON, test for 0 volts between the low reference circuit terminals of the appropriate sensor listed below and ground .
  3. • LF Sensor circuit terminal 34
    • RF Sensor circuit terminal 6
    If not the specified value, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the wheel speed sensor.
  4. Test for 0 volts between the signal circuit terminals of the appropriate sensor listed below and ground.
  5. • LF Sensor circuit terminal 21
    • RF Sensor circuit terminal 18
    If not the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the wheel speed sensor.
  6. Ignition OFF, test for infinite resistance between the low reference terminals of the appropriate sensor listed below and ground.
  7. • LF Sensor circuit terminal 34
    • RF Sensor circuit terminal 6
    If not the specified value, test the low reference circuit for a short to ground. If the circuit tests normal, replace the wheel speed sensor.
  8. Test for infinite resistance between the following signal circuit terminals of the appropriate sensor listed below and ground.
  9. • LF Sensor circuit terminal 21
    • RF Sensor circuit terminal 18
    If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the wheel speed sensor.
  10. Ignition OFF, disconnect the harness connector at the wheel speed sensor.
  11. Test for less than 1 ohm of resistance between the low reference terminals of the appropriate sensor listed below.
  12. • LF Sensor circuit terminals 34 and 2
    • RF Sensor circuit terminals 6 and 2
    If not within the specified range, test the low reference circuit for an open/high resistance.
  13. Test for less than 1 ohm of resistance between the following signal circuit terminals of the appropriate sensor listed below.
  14. • LF Sensor circuit terminals 21 and 1
    • RF Sensor circuit terminals 18 and 1
    If not within the specified range, test the signal circuit for an open/high resistance.
  15. Test for infinite resistance between the low reference circuit and the signal circuit of the appropriate sensor listed below and ground.
  16. • LF Sensor circuit terminal 34 and 21
    • RF Sensor circuit terminal 6 and 18
    If not the specified value, test the appropriate circuit for a short together.
  17. If all circuits test normal, replace the EBCM.

Component Testing

  1. Ignition OFF, disconnect the harness connector at the wheel speed sensor .
  2. Connect a test lamp between B+ and the wheel speed sensor signal circuit terminal 1.
  3. Test for 4-8 mA on the low reading between the low reference terminal 2 and ground when spinning the wheel very slow.
  4. If not within the specified range, replace the wheel speed sensor.
  5. Test for 12-16 mA on the high reading between the low reference terminal 2 and ground when spinning the wheel very slow.
  6. If not within the specified range, replace the wheel speed sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Front Wheel Speed Sensor Replacement
    •  Control Module References for EBCM replacement, setup, and programming