GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 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.

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 seconds:

    • The EBCM commands the solenoid valve relay on and battery voltage is not present at the solenoid valves.
    •  The EBCM commands the solenoid valve relay off and battery voltage is present at the solenoid valves.

Action Taken When the DTC Sets

If equipped, the following actions occur:

    • The EBCM disables the ABS/TCS/VSES for the duration of the ignition cycle.
    • ACC Braking is Degraded.
    • DRP is degraded.
    • The ABS indicator turns ON.
    • The Traction Control indicator turns ON.
    • The DIC displays the Service Stability System message.
    • The red Brake warning indicator turns ON.

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

Diagnostic Aids

The system 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. 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 in Vehicle DTC Information

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 in Wiring Systems

3

Important: Perform the setup procedure for the electronic brake control module (EBCM). An unprogrammed EBCM will result in the following conditions:

   • Inoperative or poorly functioning system operations
   • The EBCM may set DTCs

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

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