Code
B0171
Generic
B — Body
Body Control Module — Internal Fault
Views:
UK: 9
EN: 15
RU: 10
AI status
Completed
Completed
100%
Causes
- BCM internal hardware failure (processor, memory, or I/O circuits)
- Corrupted or failed BCM firmware/software
- Intermittent or low battery/charging system voltage during module operation
- Poor or corroded ground or power connections to the BCM
- Water intrusion, moisture, or physical damage at the BCM or connector
- Electrical overstress from shorts, voltage spikes, or jump-start events
Symptoms
- One or more body functions inoperative or intermittent (lighting, door locks, windows, wipers, HVAC controls)
- Multiple unrelated body system faults present simultaneously
- Loss of BCM communication on vehicle network (CAN/LIN) or intermittent CAN errors
- Warning lights or message center alerts related to body electronics
- Vehicle may enter safe-mode behavior for affected circuits or disable non-essential features
What to check
- Read all stored codes and freeze-frame data from BCM and other modules with a capable scan tool
- Check for related communication codes (U0xxx) indicating bus issues
- Verify battery state of charge and charging system voltage under static and cranking conditions
- Visually inspect BCM, its mounting area and connectors for corrosion, water ingress, damage or loose pins
- Check all related fuses, fusible links and relays feeding the BCM
- Verify ground and supply continuity at the BCM power and ground pins
Signal parameters
- Battery/supply voltage to BCM: ~12–14.5 V (engine off/charging); should not drop below ~11 V during normal operation
- VBAT sense and Ignition-switched supply present when key on (KOEO)
- Ground continuity: near 0 Ω between BCM ground pin and chassis ground
- CAN bus: modules should exchange messages; check for CAN activity and expected message rate (vehicle-specific; often 125/250/500 kb/s)
- Sleep/wake signals: BCM should enter/exit sleep state according to wake-line activity (vehicle-specific)
- No persistent high-current draw from BCM when vehicle is sleeping (parasitic drain should be within spec)
Diagnostic algorithm
- Connect manufacturer-capable scan tool. Record B0171 freeze-frame, all current and historic codes from BCM and network modules. Note ignition state and voltage at time of fault.
- Check battery and charging system. Ensure battery is fully charged and alternator output is within spec. Retest if voltage was low during the event.
- Visually inspect BCM and connectors for corrosion, water damage, broken pins, or loose mounting. Repair or replace damaged connectors/wiring.
- Verify fuses, fusible links and relay operation for BCM power circuits. Repair any open circuits.
- Verify power and ground at BCM pins with meter. Repair poor grounds/power feeds and retest code presence.
- Monitor CAN/LIN traffic with scope or scan tool. If BCM is not communicating or shows bus errors, trace wiring and check termination resistances.
- Attempt soft reset/reboot of BCM via scan tool. If available, apply manufacturer-specified reflash or firmware update per service instructions.
- If fault persists after wiring, power, ground, and software checks, consider module replacement. Ensure replacement BCM is a correct part and is programmed/configured to vehicle per factory procedures (immobilizer pairing, calibration, VIN programming as required).
- After repair/replacement clear codes, perform functional tests of affected systems and a road test. Re-scan to confirm no return of B0171 and no related network faults.
- If uncertain or failures continue, consult manufacturer technical service bulletins and escalate to module-level diagnostics or supplier support.
Likely causes
- Corroded connector or poor ground at BCM
- Battery voltage low or unstable during a self-test or reflash attempt
- Moisture/contamination inside BCM housing
- Corrupted firmware or failed software update
Fault status
Status
BCM internal fault detected. The module reported an internal hardware or software error and may be operating in restricted mode or not responding on the vehicle network. Further diagnosis required to identify wiring, power/ground, firmware or module replacement.
Repair difficulty: Hard
Diagnostic time: 1.5-4.0 hours
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