Diagnostic Test

WARNING: This page is about a different car, the 2016 Jeep Wrangler and 2015 Jeep Wrangler. However, it is still accessible from the selected car via links, so may be relevant.

CHECK FOR A DTC C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE
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 the DTCs.
3. With the scan tool, read and record the Environmental Data to help identify the conditions in which the DTC was set.
4. With the scan tool, erase the DTCs.
5. Start the engine.
6. Slowly press and release the brake pedal.
7. With the scan tool, read and record the DTCs.
  Does the scan tool display: C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE?
  
  Yes
  - Go To 2
  No
  - Perform the ABS-INTERMITTENT CONDITION TEST. Refer to STANDARD PROCEDURE .
HCU/ECU ISOLATION
1. Turn the ignition off.
2. Separate the ECU from the HCU.
3. Turn the ignition on.
4. With the scan tool, monitor the 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 the ABS VERIFICATION TEST. Refer to STANDARD PROCEDURE .
  No
  - Replace the ECU in accordance with the Service Information.
  - Perform the ABS VERIFICATION TEST. Refer to STANDARD PROCEDURE .