Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJEEP2007GRAND CHEROKEE 2WD V6-3.7L VIN KREPAIR AND DIAGNOSISA L L DIAGNOSTIC TROUBLE CODES ( DTC )TESTING AND INSPECTIONC CODE CHARTSC121E
2007 Jeep Grand Cherokee 2WD V6-3.7L VIN K
C121E
2007 Jeep Grand Cherokee 2WD V6-3.7L VIN KSECTION C121E
C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE
For a complete wiring diagram, refer to Diagrams/Electrical. Electrical Diagrams
- 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.
Diagnostic Test
1. 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.
Turn the ignition on.
With the scan tool, read and record DTCs.
With the scan tool, read and record Freeze Frame information.
With the scan tool, erase DTCs.
Start the engine.
Depress and release the brake pedal.
With the scan tool, read and record DTCs.
Does the scan tool display: C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE?
Yes
- Go To 2
No
-
- Refer to the ABS-INTERMITTENT CONDITION TEST. ABS Intermittent Condition Test
2. RECHECK FOR A DTC C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE
Turn the ignition on.
With the scan tool, read and record DTCs.
With the scan tool, read and record Freeze Frame information.
With the scan tool, erase DTCs.
Start the engine.
Depress and release the brake pedal.
With the scan tool, read and record DTCs.
Does the scan tool display: C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE?
Yes
- Go To 3
- Perform ABS VERIFICATION TEST. ABS Verification Test
No
- Test complete
3. 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 200 psi
Yes
- Replace the HCU.
- Perform ABS VERIFICATION TEST. ABS Verification Test
No
- Replace the ECU.
- Perform ABS VERIFICATION TEST. ABS Verification Test
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.