For 1990-2009 cars

### Circuit Description

The ABS control module uses a relay to control the valve solenoids. When the ignition is in the Run position, the module energizes the relay winding to switch the battery voltage that supplies the solenoids. The module will disable the relay when the ignition is off, or a fault is detected.

### Conditions for Setting the DTC

DTC C0121 will set if:

• | The control module commands the relay on, but does not sense battery voltage at the solenoids.

• | The control module commands the relay off, and senses battery voltage at the solenoids.

When DTC C0121 sets:

• | The ABS telltale will be on.

• | The ABS control module will disable the ABS, the TCS, and the DRP.

### Diagnostic Aids

This relay is inside the ABS control module and is NOT serviceable.

### Test Description

The number below refers to step number on the diagnostic table.

1. This step determines if the DTC is current.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views
1 | Did you perform the Diagnostic System Check? | Go to Step 2 | Go to Basic Knowledge and Tools Required
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.

Does the DTC reset?

Go to Step 3

Go to Diagnostic Aids

3 | Test the battery positive voltage circuit for an open, high resistance, or a short to ground. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 5 | Go to Step 4
4 | Replace the Electronic Brake Control Module (EBCM). Refer to ABS Control Module Replacement . Did you complete the replacement? | Go to Step 5 | --
5 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK