Circuit Description
Each of the 4 brake circuits on the vehicle 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 ABS indicator turns ON. |
| • | The ABS function to the right front wheel is disabled. |
| • | The EBCM illuminates the RGT, FRT and MOD LEDs. |
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 | ||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
2 |
Do the LEDs on the EBCM indicate a current air pressure modulator fault? | -- | Go to Step 3 | Go to Diagnostic Aids | ||||||||
3 |
Does the resistance measure within the specified range? | 3.5-5 ohms | Go to Step 4 | Go to Step 6 | ||||||||
4 | Use a DMM in order to measure the resistance between the modulator exhaust control circuit and the modulator supply voltage circuit. Does the resistance measure within the specified range? | 3.5-5 ohms | Go to Step 5 | Go to Step 6 | ||||||||
5 | Use a DMM in order to measure the resistance between the modulator exhaust control circuit and the modulator hold control circuit. Does the resistance measure within the specified range? | 7-10 ohms | Go to Step 9 | Go to Step 6 | ||||||||
6 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | ||||||||
7 | Inspect for poor connections at the harness connector of the air PMV. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 | ||||||||
8 | Replace the air PMV. Refer to Front Brake Pressure Modulator Valve Replacement or Rear Brake Pressure Modulator Valve Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
9 | 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 11 | Go to Step 10 | ||||||||
10 | Replace the EBCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||
11 |
Do the same red LEDs illuminate? | -- | Go to Step 3 | Go to Step 12 | ||||||||
12 | Do any red LEDs illuminate? | -- | System OK | |||||||||
