U0171
- Network & Communication
- Generic (SAE)
- Safety
Stop driving
Continuing to drive risks injury or major mechanical damage. Shut the engine off when it is safe to do so.
Lost Communication with Restraints Rear Sensor "A"
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
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.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Continuing to drive risks injury or major mechanical damage. Shut the engine off when it is safe to do so.
- Urgency
- Stop driving
- Will it pass emissions
- Not affected
- Check engine light
- Solid
- 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
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Rear sensor unpowered | Very common | — |
| 2 | Wiring to rear sensor broken | Common | — |
| 3 | Gateway module routing CAN messages incorrectly | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- Restraints Rear Sensor
- CAN Bus Wiring
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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