GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 Terraza Ext. 🢒 Brakes 🢒 Park Brake 🢒 DTC C0121

Circuit 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.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0121 Valve Relay Circuit

Conditions for Running the DTC
    • The ignition is ON.
    • Ignition voltage is greater than 8 volts.

Conditions for Setting the DTC

One of the following conditions exists for 0.23 second:

    • The EBCM commands the solenoid valve relay on and battery voltage is less than 8 volts at the solenoid valves.
    • An internal EBCM relay driver fault is not detected.

Action Taken When the DTC Sets

If equipped, the following actions occur:

    • The EBCM disables the antilock brake system (ABS).
    • The ABS indicator turns ON.
    • Dynamic rear proportion (DRP) function is degraded (w/NW7 or JL4).
    • DRP function is disabled (w/o NW7).
    • The red brake warning turns ON (w/o NW7).
    • The EBCM disables Traction Control System (TCS).
    • The EBCM disables vehicle stability enhancement system (VSES).

Conditions for Clearing the DTC
    • The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
    • The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids

The solenoid valve relay is integral to the EBCM. The relay is not serviceable.

Test Description

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

  1. This step determines whether the DTC is current.

Step

Action

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Use the scan tool in order to clear the DTCs.
  2. Cycle the ignition to the OFF position.
  3. Start the engine.
  4. In PARK or NEUTRAL, release the brake.
  5. Turn OFF the engine.

Does the DTC reset?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

Replace the electronic brake control module (EBCM). Refer to Control Module References for replacement, setup, and programming.

Did you complete the repair?

Go to Step 4

--

4
  1. Use the scan tool in order to clear the DTCs.
  2. Cycle the ignition to OFF and then ON.

Does the DTC reset?

Go to Step 2

System OK