For 1990-2009 cars

### Circuit Description

Each of the 4 brake circuits on the vehicle passes through a separate air pressure modulator valve. The 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 left rear wheel is disabled.

• | The EBCM illuminates the LFT, RER 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:

• | Testing for Electrical Intermittents

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Connector Repairs

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Air Antilock Brake System Schematics
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Air ABS
2 |

1. Turn the ignition ON.
2. Observe the LEDs on the EBCM after the ignition has been ON for 10 seconds.

Do the LEDs on the EBCM indicate a current air pressure modulator fault?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Disconnect from the EBCM, the harness connector or connectors containing the modulator hold control circuit, exhaust control circuit and the modulator supply voltage circuit of the indicated air pressure modulator valve.
2. 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 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? | 7.0-10 ohms | Go to Step 9 | Go to Step 6
6 |

1. Disconnect the air pressure modulator valve harness connector. Refer to Front Brake Pressure Modulator Valve Replacement or Rear Brake Pressure Modulator Valve Replacement .
2. Test the modulator valve circuits between the modulator valve harness connector and the EBCM harness connector. Test each for the following:

• | An open

• | A short to ground

• | A short to voltage

• | Shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 pressure modulator valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
8 | Replace the air pressure modulator valve. 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 in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
10 | Important: Following EBCM replacement, perform the EBCM self-configuration procedure. Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Perform the magnetic reset procedure. Refer to Status Lamp Resetting .
2. Operate the vehicle within the Conditions for Running the Diagnostic Fault.

Do the same red LEDs illuminate?

--

Go to Step 3

Go to Step 12

12 | Do any red LEDs illuminate? | -- | Go to Diagnostic System Check - Air ABS | System OK