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 MANUALSJEEP2023GRAND CHEROKEE TRAILHAWK 4XEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 61 (5.7L - DTCS P3401 TO U0404)DTC TROUBLESHOOTINGU0129 LOST COMMUNICATION WITH BRAKE SYSTEM CONTROL MODULE 1POSSIBLE CAUSES
2023 Jeep Grand Cherokee Trailhawk 4xe
Possible Causes
2023 Jeep Grand Cherokee Trailhawk 4xeSECTION Possible Causes
WARNING: This page is about a different variant/trim than selected.
| POSSIBLE CAUSES |
|---|
| FAULTY HYDRAULIC ASSEMBLY (BPP AND BRAKE SIMULATOR SENSORS ARE INTERNAL) |
| FAULTY BRAKE SYSTEM MODULE (BSM) |
The (U0121, U0129) Loss of Communication faults can set for any of the following:
| POSSIBLE CAUSES |
|---|
| BATTERY OR IGNITION SUPPLY TO BSM OPEN OR SHORTED TO GROUND |
| BSM GROUND CIRCUIT OPEN/HIGH RESISTANCE |
| BSM CAN BUS CIRCUITS SHORTED TO VOLTAGE |
| BSM CAN BUS CIRCUITS SHORTED TO GROUND |
| BSM CAN BUS CIRCUITS OPEN/HIGH RESISTANCE |
| FAULTY BRAKE SYSTEM CONTROL MODULE (BSCM) |
The Wheel Speed Sensor faults can set for any of the following:
| POSSIBLE CAUSES |
|---|
| SNA OR ERROR MESSAGE FROM BSCM |
| WSS SIGNAL CIRCUITS SHORTED TO VOLTAGE |
| WSS SIGNAL CIRCUITS SHORTED TO GROUND |
| WSS SIGNAL CIRCUITS OPEN/HIGH RESISTANCE |
| WSS GROUND CIRCUIT OPEN/HIGH RESISTANCE |
| DAMAGED TONE WHEEL |
| FAULTY WHEEL SPEED SENSOR |
| FAULTY BRAKE SYSTEM CONTROL MODULE (BSCM) |
RENDER: 1.0x
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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.