C121D-BRAKE PRESSURE SENSOR CIRCUIT

For a complete wiring diagram, refer to the Wiring Information.

When Monitored:
With the ignition on.
Set Condition:
When the Anti-Lock Brake Module indicates that the Brake Pressure Sensor Signal is out of range.

Possible Causes
AIR IN BRAKE SYSTEM/WORN MECHANICAL COMPONENTS
ECU INTERNAL FAILURE
HCU INTERNAL FAILURE

1. CHECK FOR A DTC C121D-BRAKE PRESSURE SENSOR CIRCUIT

NOTE: This DTC must be active for the results of this test to be valid.

1.	Turn the ignition on.

2.	With the scan tool, read and record DTCs.

3.	With the scan tool, read and record Freeze Frame information.

4.	With the scan tool, erase DTCs.

5.	Start the engine.

6.	Slowly depress and release the brake pedal.

7.	With the scan tool, read and record DTCs.

Does the scan tool display: C121D-BRAKE PRESSURE SENSOR CIRCUIT?

Yes

2. HCU/ECU ISOLATION

1.	Turn the ignition off.

2.	Separate the ECU from the HCU.

3.	With the scan tool, monitor brake pressure.

Does the scan tool display brake pressure above 218 bar (3162 psi)?

Yes

Replace the HCU in accordance with the Service Information.
Perform ABS VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Antilock Brake (ABS) - Standard Procedure).

Replace the ECU in accordance with the Service Information.
Perform ABS VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Antilock Brake (ABS) - Standard Procedure).