GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2008 🢒 Isuzu H-Series 🢒 Brakes 🢒 Air Antilock Brake System 🢒 Status Lamps Illuminated - LFT, STEERAXLE, and MOD

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.

Circuit/System Description

Each of the 4 brake circuits passes through a seperate air pressure modulator valve. 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 STEERAXLE, LFT, and MOD LEDs.
    • The ABS indicator lamp turns ON.
    • The ABS function to the left front wheel is disabled.

Conditions for Clearing the Diagnostic Fault
    • Repair the condition responsible for illuminating the status lamps.
    • Perform the Status Lamp Resetting procedure. Refer to Status Lamp Resetting.

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

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

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
  1. Ignition OFF, disconnect the brake pressure modulator valve harness connector at the EBCM.
  2. Ignition OFF, test for 3.5-5 ohm between the brake pressure modulator valve exhaust control circuit terminal A and the supply voltage circuit terminal B.
    3. ⇒ 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 brake pressure modulator valve.
  3. Ignition OFF, test for 7.0-10 ohm between the brake pressure modulator exhaust control circuit terminal A and the brake pressure modulator terminal hold control circuit terminal C.
    4. ⇒ 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 brake pressure modulator valve.
    ⇒ If within the specified range, test or replace the EBCM.
  4. If all circuits test normal, replace the brake pressure modulator valve.

Component Testing
  1. Ignition OFF, disconnect the BPMV harness connector at the EBCM.
  2. Test for 7.0-10 ohms between the BPMV modulator exhaust control circuit terminal A and the modulator hold control circuit terminal C.
    3. ⇒ If not within the specified range, replace the BPMV.
  3. Test for infinite resistance between each terminal and the sensor housing/case.
    4. ⇒ If less than the specified value, replace the BPMV.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Front Brake Pressure Modulator Valve Replacement
    •  Rear Brake Pressure Modulator Valve Replacement
    •  Control Module References for EBCM replacement, setup, and programming.