The green VLT LED remains illuminated when the ignition is ON. The VLT LED flashes when system voltage is 9-11 volts or greater than 17 volts. The VLT LED turns OFF when voltage to the electronic brake control module (EBCM) is less than 9 volts.

The ignition is ON.

The EBCM detects low or high system voltage.

Important:  Upon replacing the electronic brake control module (EBCM) perform the Bendix RDU magnet reset procedure. Refer to Status Lamp Resetting.

Ensure the charging system is operating normally. Refer to Charging System Test and Symptoms - Engine Electrical.

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

Control Module References

1. Ignition OFF, disconnect the ABS Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignition 3 circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the ignition 3 circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition 3 fuse or circuit breaker is open, test or replace the fuse or breaker.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground.

5. Disconnect the harness connector at the EBCM.
6. Test for less than 2.0 ohm between the EBCM ground circuit and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the EBCM.
8. Connect a 3 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the EBCM is activated.

⇒	If the component does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the EBCM.

9. Connect a test lamp between the ignition 3 circuit terminal 86 and the control circuit terminal 85.
10. Command the ABS Relay ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuits tests normal, replace the EBCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the EBCM.

11. If all circuits test normal, test or replace the ABS Relay.

1. Ignition OFF, disconnect the ABS Relay.
2. Test for 0-2.0 ohms between terminals 85 and 86.

⇒	If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 3 A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.