Circuit Description
The electronic brake control module (EBCM) activates the traction control (TC) modulator valve by supplying 12 volts to the TC modulator valve high reference circuit and supplying ground to the TC modulator valve low reference circuit. When the TC modulator valve is energized, an internal valve opens and air pressure is applied to the drive axle brake pressure modulator valve (BPMV).
Conditions for Running the Diagnostic Fault
| • | The ignition is ON. |
| • | The EBCM is calibrated for traction control. |
Conditions for Setting the Diagnostic Fault
The EBCM detects an open or shorted TC modulator or circuitry.
Action Taken When the Diagnostic Fault Sets
| • | The TC system is disabled. |
| • | The Traction Off indicator on turns ON. |
| • | Driver is unable to re-enable the TC system. |
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 the following:
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 Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
2 |
Do the LEDs on the EBCM indicate a current traction control modulator fault? | -- | Go to Step 3 | Go to Diagnostic Aids | ||||||||
3 |
Does the resistance measure within the specified range? | 0.5-12 ohms | Go to Step 7 | Go to Step 4 | ||||||||
4 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 5 | ||||||||
5 | Inspect for poor connections at the harness connector of the TC modulator valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 | ||||||||
6 | Replace the TC modulator valve. Refer to Rear Air Brake Relay Valve Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
7 | Inspect for poor connections at the harness connector for the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||
8 | Replace the EBCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
9 | Operate the vehicle within the Conditions for Running the Diagnostic Fault. Do the same red LEDs illuminate? | -- | Go to Step 3 | Go to Step 10 | ||||||||
10 | Do any red LEDs illuminate? | -- | System OK | |||||||||
