Diagnostic Instructions
Circuit/System Description
Each of the 4 brake circuits passes through a separate air pressure modulator valve (PMV). The electronic brake control module (EBCM) uses each modulator valve to hold, decrease or increase the pressure in an individual brake circuit.
Conditions for Running the Diagnostic Fault
The ignition is ON.
Conditions for Setting the Diagnostic Fault
The EBCM detects an open or shorted hold or exhaust solenoid or open or shorted circuitry.
Action Taken When the Diagnostic Fault Sets
| • | The Bendix Remote Diagnostic Unit (RDU), illuminates the DRIVEAXLE, LFT, and MOD LEDs. |
| • | The ABS indicator lamp turns ON. |
| • | The ABS function to the left rear wheel is disabled. |
Conditions for Clearing the Diagnostic Fault
| • | Repair the condition responsible for illuminating the status lamps. |
Diagnostic Aids
Important: Upon replacing the electronic brake control module (EBCM) perform the Bendix RDU magnet reset procedure. Refer to
Status Lamp Resetting.
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
Ignition ON, observe the Bendix Remote Diagnostic Unit (RDU) after 10 seconds. The LEDs on the RDU should indicate a current air pressure modulator fault.
Circuit/System Testing
- Ignition OFF, disconnect the brake pressure modulator valve (BPMV) harness connector at the EBCM.
- Ignition OFF, test for 3.5-5 ohm between the BPMV exhaust control circuit terminal A and the supply voltage circuit terminal B.
| ⇒ | If not within the specified range, test the supply voltage, exhaust valve, and hold control circuits for an open/high resistance, short to ground, short to voltage, and shorted together. If the circuit tests normal, replace the BPMV. |
- Ignition OFF, test for 7.0-10 ohm between the brake pressure modulator exhaust control circuit terminal A and the BPMV terminal hold control circuit terminal C.
| ⇒ | If not within the specified range, test the supply voltage, exhaust valve, and hold control circuits for an open/high resistance, short to ground, short to voltage, and shorted together. If the circuit tests normal, replace the BPMV. |
| ⇒ | If within the specified range, test or replace the EBCM. |
- If all circuits test normal, replace the BPMV.
Component Testing
- Ignition OFF, disconnect the BPMV harness connector at the EBCM.
- Test for 7.0-10 ohms between the BPMV modulator exhaust control circuit terminal A and the modulator hold control circuit terminal C.
| ⇒ | If not within the specified range, replace the BPMV. |
- Test for infinite resistance between each terminal and the sensor housing/case.
| ⇒ | If less than the specified value, replace the BPMV. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
