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 C0121 : ABS Relay Circuit

### Circuit/System Description

When the antilock brake system (ABS) is active, the valve relay provides voltage to actuate the solenoid valves. The valves do not use this voltage unless the ABS control module provides the ground for each solenoid coil.

DTC C0121 will set if the valve relay voltage is low or if the relay supply line is at 12 volts when the ABS control module is not requesting it. This diagnostic trouble code (DTC) will also set if the ABS control module detects 3 or more solenoid valve circuits are open or shorted during the self-test.

This procedure checks whether there is a poor ground connection for the electronic brake control module (EBCM).

### Conditions for Running the DTC

• | Vehicle speed is greater than 6 km/h (4 mph) with the brake pedal not applied.

| OR

• | Vehicle speed is greater than 15 km/h (9 mph) and the brake pedal is actuated.

### Conditions for Setting the DTC

• | A connector terminal is corroded.

• | The wiring harness is damaged.

• | The ground terminal is not conducting properly.

• | The EBCM is defective.

### 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.

• | The EBD warning indicator turns ON.

If the failure is intermittent, the EBCM will enable the system at the next ignition cycle and set a history DTC.

### 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 Testing

1. Ignition OFF, disconnect the EBCM connector.
2. Measure for 0 ohms between the EBCM ground circuits and ground.

⇒ | If more than 0 ohms, repair open or high resistance in ground circuit.

⇒ | If all circuits test normal replace the EBCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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