U0171: Lost Communication with Restraints Rear Sensor "A"
Standardized SAE J2012 code · U01xx — Lost communication with modules
What does U0171 mean?
The Restraints Rear Sensor "A" has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages. A rear crash sensor is unreachable, affecting rear airbag deployment. Safety-critical. Typical causes are loss of power or ground at the module, an open or shorted CAN/LIN bus wire, a connector fault, or an internal module failure.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- High Rear sensor unpowered
- Medium Wiring to rear sensor broken
- Low Gateway module routing CAN messages incorrectly
Likelihood is a general estimate across vehicles; your make and model may differ.
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