Diagnostic Instructions
DTC Descriptor
DTC C0121 00: Valve Relay Circuit Malfunction
Circuit/System 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.
Conditions for Setting the DTC
| • | Solenoid valve relay is commanded on and the EBCM does not see battery
voltage at the solenoid valves. |
| • | EBCM commands the solenoid valve relay off and battery voltage is still
present at the solenoid valves. |
Action Taken When the DTC Sets
| • | The EBCM disables the Antilock Brake System (ABS)/Traction Control System
(TCS)/Electronic Stability Control (ESP)/ for the duration of the ignition cycle. |
| • | The multi function display (MFD) displays the ABS Fault message. |
| • | The multi function display (MFD) displays the Traction Ctrl Off message. |
| • | The multi function display (MFD) displays the Stability Ctrl Off message. |
Conditions for Clearing the DTC
| • | The condition for setting the DTC is no longer present. |
| • | The EBCM automatically clears the history DTC when a current DTC is not
detected in 100 consecutive drive cycles. |
| • | The DTC can be cleared using a scan tool. |
Diagnostic Aids
The solenoid valve relay is integral to the brake modulator assembly/EBCM. The
solenoid valve relay is not serviceable.
Reference Information
Schematic Reference
Antilock Brake System Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
Scan Tool Reference
Control Module References
Circuit/System Verification
With scan tool installed, clear the DTCs then drive the vehicle in a straight
line at a speed greater than 20 km/h (13 mph).
Circuit/System Testing
- Ignition OFF, disconnect the EBCM harness connector.
- Test for less than 1.0 ohm of resistance between the valve relay ground
circuit terminal and ground.
| ⇒ | If greater than the specified range, test the valve relay ground circuit for
an open/high resistance. |
- Connect a test lamp between the valve relay supply voltage circuit terminal
and the ground circuit terminal.
| ⇒ | If the test lamp is ON, replace the EBCM. |
| ⇒ | If the test lamp is OFF, test the valve relay supply voltage circuit for a short
to ground or an open/high resistance. |
Repair Instructions
