Circuit Description
As the wheel spins, the wheel speed sensor produces an AC signal. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the wheel speed.
Conditions for Running the Diagnostic Fault
| • | The ignition is ON. |
| • | The vehicle speed is greater than 26 km/h (16 mph). |
Conditions for Setting the Diagnostic Fault
| • | Open wheel speed sensor or wheel speed sensor wiring. |
| • | Shorted wheel speed sensor or wheel speed sensor wiring. |
| • | Wheel speed signal not present or does not conform to design criteria. |
Action Taken When the Diagnostic Fault Sets
| • | The ABS indicator lamp turns ON. |
| • | The ABS is disables on that wheel only. |
| • | The EBCM illuminates the RER, LFT, and SEN LEDs. |
Conditions for Clearing the Diagnostic Fault
| • | Repair the condition responsible for illuminating the status lamps. |
| • | Perform the Status Lamps Reset Procedure. |
Diagnostic Aids
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , Testing for Electrical Intermittents and Wiring Repairs in Wiring Systems.
If the customer's concern is that the ABS indicator is on only during humid conditions such as rain, snow or vehicle wash, thoroughly inspect the wheel speed sensor circuits for signs of water intrusion. Use the following procedure in order to help isolate the problem area:
- Spray the suspected area with a 5 percent salt water solution: 10 grams (2 teaspoons) of salt to 200 ml (12 oz) of water.
- Operate the vehicle at a speed greater than 19 km/h (12 mph) for at least 30 seconds.
Repair or replace the suspect harness if the DTC sets.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for the correct bearing play. Excessive bearing play can cause wheel speed sensor air gap to exceed specification. Wheel speed sensor air gap must be reinspected after a repair is made to correct excessive bearing play.
-
Measure the resistance value of the wheel speed sensor in order to determine if the sensor has a valid resistance value.
-
Ensures the wheel speed sensor is generating a valid AC voltage output.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Air Antilock Brake System Schematics Connector End View Reference: Air Brake System Component Views | ||||||||||||
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |||||||||
2 |
Do the LEDs on the EBCM indicate a current wheel speed sensor fault? | 26 km/h (16 mph) | Go to Step 3 | Go to Diagnostic Aids | ||||||||
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 4 | |||||||||
4 | Inspect the wheel speed sensor in order to ensure the sensor is installed and retained properly for proper air gap. Refer to Front Wheel Speed Sensor Replacement or Rear Wheel Speed Sensor Replacement . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 5 | ||||||||
Does the resistance measure within the specified range? | 1500-2500 ohms | Go to Step 6 | Go to Step 8 | |||||||||
Does the AC voltage measure greater than the specified value? | 800 mV | Go to Step 7 | Go to Step 8 | |||||||||
7 | Inspect for poor connections at the harness connector of the wheel speed sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||
8 | Replace the wheel speed sensor. Refer to Front Wheel Speed Sensor Replacement or Rear Wheel Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||
9 | Test the wheel speed sensor circuits for the following:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||
10 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
11 |
Important: Following EBCM replacement, perform the EBCM self-configuration procedure. Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||
12 |
Do the same red LEDs illuminate? | -- | Go to Step 3 | Go to Step 13 | ||||||||
13 | Do any red LEDs illuminate? | -- | System OK | |||||||||
