Diagnostic Instructions
Circuit/System Description
As the wheel spins, the wheel speed sensor (WSS) 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
| • | Vehicle speed is greater than 26 km/h (16 mph). |
Conditions for Setting the Diagnostic Fault
| • | Shorted WSS or WSS Wiring. |
| • | Wheel speed signal not present or does not conform to design criteria. |
Action Taken When the Diagnostic Fault Sets
| • | The Bendix Remote Diagnostic Unit (RDU), illuminates the DRIVEAXLE, LFT, and SEN LEDs. |
| • | The ABS indicator lamp turns ON. |
| • | The ABS operates using the input from the other rear WSS. |
Conditions for Clearing the Diagnostic Fault
| • | Repair the condition responsible for illuminating the status lamps. |
Diagnostic Aids
Important: Upon any electronic brake control module (EBCM), or wheel speed sensor (WSS) replacement perform the Bendix RDU magnet reset procedure. Refer to
Status Lamp Resetting.
| • | Test the suspect WSS circuits for being shorted together. |
If the customer concern is that the ABS indicator is ON only during humid conditions such as rain, snow or vehicle wash, thoroughly inspect the WSS 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 26 km/h (16 mph) for at least 30 seconds.
Repair or replace the suspect harness if the diagnostic fault sets.
Reference Information
Schematic Reference
Air Antilock Brake System Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Air ABS Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
Circuit/System Verification
- Operate the vehicle at a speed greater than 26km/h (16mph).
- Observe the Bendix Remote Diagnostic Unit (RDU). The LEDs on the RDU should indicate a current wheel speed sensor (WSS) fault.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the wheel speed sensor (WSS).
- Ignition OFF, test for less than 1800 - 2200 ohm between the low reference circuit terminal B and ground.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the electronic brake control module (EBCM). |
- Ignition ON, verify the DMM WSS signal circuit A/C voltage across the WSS, while spinning the wheel as fast as possible. The WSS DMM A/C voltage should measure greater than 800 mV.
| ⇒ | If less than the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the EBCM. |
- Install a 3 A fused jumper between the WSS signal circuit terminal A and the low reference circuit terminal B. Verify the DMM WSS A/C voltage is less than 800 mV. While turning the wheel as fast as you can.
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the EBCM. |
- If all circuits test normal, test or replace the WSS.
Component Testing
- Ignition OFF, disconnect the harness connector at the WSS.
- Test for 1800-2200 ohms between the WSS signal terminal A and the low reference circuit terminal B.
| ⇒ | If not within the specified range, replace the WSS. |
- Test for infinite resistance between each terminal and the sensor housing/case.
| ⇒ | If less than the specified value, replace the WSS. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
