For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC C0550: Electronic Control Unit (ECU) Performance

### Circuit/System Description

The antilock brake system (ABS) control module performs various diagnostic checks on itself. If it finds a problem, it sets DTC C0550.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | A connector terminal is corroded.

• | The EBCM is malfunctioning.

### Action Taken When the DTC Sets

• | The antilock brake system (ABS) is disabled.

• | The ABS warning indicator turns ON.

• | The electronic brake force distribution (EBD) is disabled.

### Conditions for Clearing the DTC

The condition for setting the DTC is no longer present and the DTC is cleared with a scan tool.

### Reference Information

#### Schematic Reference

Antilock Brake System Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Connector Repairs

#### Scan Tool Reference

Electronic Brake Control Module Scan Tool Information

### Circuit/System Verification

With scan tool check if any other DTCs are set.

⇒ | If other DTCs are present, diagnose those DTCs prior to DTC C0550.

### Circuit/System Testing

1. With the ignition OFF, disconnect the EBCM connector.
2. Measure for 10-16 volts between the B+ circuits and ground at the EBCM connector.

⇒ | If voltage is not as specified, repair short to ground, open or high resistance in B+ circuits.

3. Measure for 10-16 volts between the Ignition voltage circuit and ground at the EBCM connector.

⇒ | If voltage is not as specified, repair short to ground, open or high resistance in ignition voltage circuit.

⇒ | If all circuits test normal, replace the EBCM.

### Component Testing

1. Disconnect the wheel speed sensor connector. Measure for the resistance across the WSS connector terminals, resistance should be above 1M ohm.

⇒ | If the resistance is below 1M ohm, replace the WSS.

2. At the wheel speed sensor, connect a 3A fused jumper wire between wheel speed sensor low reference terminal and the low reference terminal of the wheel speed harness connector. Set up a DMM to measure current flow (mA/A). Connect the positive terminal of the DMM to the wheel speed sensor signal terminal at the wheel speed sensor harness connector and the negative lead to the wheel speed sensor signal terminal of the wheel speed sensor. Spin the wheel very slowly. Measure for 4-8 mA on the low reading and 12-16 mA on the high reading.

⇒ | If the low amperage output of the wheel speed sensor signal circuit is below 4 mA or above 8 mA replace the wheel speed sensor.

⇒ | If the high amperage output of the wheel speed sensor signal circuit is below 12 mA or above 16 mA replace the wheel speed sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for EBCM and BPMV replacement, setup, and programming