For 1990-2009 cars

### Diagnostic Instructions

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

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

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

### DTC Descriptor

DTC C0121 00: Valve Relay Circuit Malfunction

### Circuit/System Description

An internal solenoid valve relay in the electronic brake control module (EBCM) supplies battery positive voltage to all solenoid valves. This voltage is referred to as system voltage. The EBCM activates the solenoid valve relay when the ignition is turned ON. Once the solenoid valve relay has been activated, The EBCM supplies ground to actuate individual solenoid valves.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | Solenoid valve relay is commanded on and the EBCM does not see battery voltage at the solenoid valves.

• | EBCM commands the solenoid valve relay off and battery voltage is still present at the solenoid valves.

### Action Taken When the DTC Sets

• | The EBCM disables the Antilock Brake System (ABS)/Traction Control System (TCS)/Electronic Stability Control (ESP)/ for the duration of the ignition cycle.

• | The multi function display (MFD) displays the ABS Fault message.

• | The multi function display (MFD) displays the Traction Ctrl Off message.

• | The multi function display (MFD) displays the Stability Ctrl Off message.

### Conditions for Clearing the DTC

• | The condition for setting the DTC is no longer present.

• | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

• | The DTC can be cleared using a scan tool.

### Diagnostic Aids

The solenoid valve relay is integral to the brake modulator assembly/EBCM. The solenoid valve relay is not serviceable.

### Reference Information

#### Schematic Reference

Antilock Brake System Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### Circuit/System Verification

With scan tool installed, clear the DTCs then drive the vehicle in a straight line at a speed greater than 20 km/h (13 mph).

### Circuit/System Testing

1. Ignition OFF, disconnect the EBCM harness connector.
2. Test for less than 1.0 ohm of resistance between the valve relay ground circuit terminal and ground.

⇒ | If greater than the specified range, test the valve relay ground circuit for an open/high resistance.

3. Connect a test lamp between the valve relay supply voltage circuit terminal and the ground circuit terminal.

⇒ | If the test lamp is ON, replace the EBCM.

⇒ | If the test lamp is OFF, test the valve relay supply voltage circuit for a short to ground or an open/high resistance.

### Repair Instructions

• | Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Brake Pressure Modulator Valve Assembly Replacement

• | Electronic Brake Control Module Replacement

• | Control Module References for EBCM replacement, setup, and programming