Circuit 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).
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0121 ABS Relay Circuit
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 following actions occur:
| • | 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 responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used.
Diagnostic Aids
It is very important to perform a thorough inspection of the wiring and the connectors. Failure to do so may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Component Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does DTC C0121 reset? | -- | Go to Step 4 | Go to Step 3 |
3 | Inspect all system wiring harness connectors and terminals for any problem that could cause an intermittent condition. Did you find and correct the condition? | -- | Go to Step 9 | -- |
4 |
Is there damage or corrosion at terminal 26? | -- | Go to Step 5 | Go to Step 6 |
5 | Repair the terminal or the connector, or replace EBCM as required. Did you complete the action? | -- | Go to Step 9 | -- |
6 | Measure the resistance from terminal 26 of the EBCM connector to a good ground. Is the resistance equal to the specified value? | 0 Ω | Go to Step 7 | Go to Step 8 |
7 | Replace the EBCM. Refer to Brake Pressure Modulator Valve Assembly Replacement. Did you complete the replacement? | -- | Go to Step 9 | -- |
8 | Repair the open or the high resistance in the ground circuit. Did you complete the action? | -- | System OK | -- |
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
