For 1990-2009 cars
ABS Components
Antilock Brake System Schematics
Handling ESD Sensitive Parts Notice

### Circuit Description

The valve relay is part of the Electronic Brake Control Module (EBCM). The EBCM turns ON the valve relay when the ignition switch is in the ON position and no malfunction exists in the ABS. The valve relay provides power to the ABS solenoid valves.

### Conditions for Running the DTC

DTC C0121 can be set within 3 seconds after the ignition switch is turned to the ON position.

### Conditions for Setting the DTC

The Electronic Brake Control Module (EBCM) detects that the valve relay is ON when actually the EBCM commanded the valve relay OFF.

### Action Taken When the DTC Sets

• | The ABS disables

• | The ABS warning indicator turns ON

### Conditions for Clearing the DTC

The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTCs function is used.

### Diagnostic Aids

Inspect for the following when diagnosing this part of the Antilock Brake System (ABS):

• | The ABS fuse

• | Open or high resistance in the pump input circuit (Terminal D)

Inspect the harness connectors for the following conditions:

• | Backed-out terminals

• | Improper mating

• | Broken locks

• | Improperly formed or damaged terminals

• | Poor terminal to wiring connections or physical damage to the wiring harness

### Test Description

The numbers below refer to step numbers on the Diagnostic Table.

1. This step determines whether the DTC is current.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform A Diagnostic System Check - ABS? | -- | Go to Step 2 | Go to Diagnostic System Check - ABS
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Use the scan tool in order to clear the DTCs.
4. Using the scan tool, cycle the solenoid valves in the Special Functions menu.
5. Read the DTCs.

Does the DTC reset?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3 | Replace the Brake Modulator Assembly. Refer to Brake Pressure Modulator Valve Assembly Replacement . Is the repair complete? | -- | Go to Step 4 | --
4 |

1. Use the scan tool in order to clear the DTCs.
2. Using the scan tool, cycle the solenoid valves in the Special Functions menu.
3. Read the DTCs.

Does the DTC reset?

--

Go to Step 2

System OK