C121D Brake pressure sensor circuit
May 30, 2017
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C121D Brake pressure sensor circuit - When the Antilock Brake System (ABS) Module indicates that Brake Pressure signal is out of range. Default action the Antilock Brake System (ABS) Module indicator light illuminate.
Possible causes C121D code
- Air in Brake System/Worn mechanical components.
- ECU internal failure.
- HCU internal failure.
Diagnose C121D-Brake pressure sensor circuit
Step 1. Check for a DTC C121D-Brake Pressure Sensor circuit
This DTC must be active for the results of this test to be valid. Turn the ignition on, with the scan tool, read and record DTC. With the scan tool, read and record Freeze Frame infromation. With the scan tool, erase DTC, start the engine, slowly depress and release the brake pedal. With the scan tool, read and record DTC.
Does the scan tool display C121D-Brake Pressure Sensor circuit ?
Yes, go to step 2.
No, perform the ABS Intermittent condition.
Step 2. HCU/ECU isolation
Turn the ignition off, separate the ECU from the HCU. With the scan tool, monitor brake pressure.
Does the scan tool display brake pressure above 218 bar (3162 psi) ?
Yes, replace the HCU, perform the ABS Verification Test.
No, replace the ECU, perform the ABS Verification Test.
Step 2. HCU/ECU isolation
Turn the ignition off, separate the ECU from the HCU. With the scan tool, monitor brake pressure.
Does the scan tool display brake pressure above 218 bar (3162 psi) ?
Yes, replace the HCU, perform the ABS Verification Test.
No, replace the ECU, perform the ABS Verification Test.
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