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Home / DTC / B1B71 — FR impact sensor

B1B71 — FR impact sensor

Detailed page for trouble code B1B71.

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B1B71

MITSUBISHI B — Body

FR impact sensor

Brand: MITSUBISHI
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or failed FR impact (accelerometer) sensor
  • Open, shorted or short-to-power/ground wiring between sensor and airbag control module
  • Corroded or disconnected sensor connector or pins
  • Water intrusion or physical damage to sensor or connector
  • Poor or missing ground or supply voltage to the sensor
  • Faulty airbag control module (less common)

Symptoms

  • SRS / airbag warning lamp illuminated on dash
  • Possible fault memory stored in airbag control module
  • Airbag system may be disabled for the front-right side
  • No obvious driveability issues (vehicle may otherwise run normally)
  • Diagnostic trouble code B1B71 present when scanned

What to check

  • Record code(s) and freeze-frame data with a compatible scan tool; note history and occurrence conditions
  • Follow OEM safety procedure: disable battery negative terminal and wait recommended time before touching SRS components
  • Visually inspect FR impact sensor, mounting, and wiring harness for damage, corrosion, contamination or disconnection
  • Check connector pins for corrosion, bent pins, and secure fit
  • Probe sensor connector with back-probe or harness adapter (per service manual) to verify supply voltage, reference and ground
  • Measure continuity and resistance of wiring between FR sensor and airbag control module; check for shorts to ground and battery

Signal parameters

  • Supply/Reference voltage: typically 5 V or 3.3 V feed to sensor (verify model-specific value in service manual)
  • Idle/rest output: often near mid-supply (e.g., ~2.5 V for a 5 V system) for analog sensors — consult OEM specs
  • Active/impact output: rapid deviation/spike from rest voltage during impact event
  • Digital sensors: data reported over dedicated SRS bus (CAN/LIN) — check for valid messages and expected IDs
  • Typical expected continuity: low-ohm connection from sensor power/ground to module; no opens or shorts to chassis/battery

Diagnostic algorithm

  1. Use a scan tool to read and record B1B71 and any other SRS codes; capture freeze-frame and clear codes to see if they return.
  2. Follow safety procedure: turn ignition off, disconnect negative battery terminal and wait manufacturer-recommended time before touching SRS components.
  3. Perform visual inspection of FR impact sensor, mount, and harness for physical damage, water intrusion, corrosion or loose connectors.
  4. Reconnect battery (per safety guidance for live tests) and back-probe sensor connector to verify reference supply voltage and ground presence with ignition on (do not deploy sensor). Compare to service manual values.
  5. Check sensor output at rest with a scope or multimeter (where applicable). For analog sensors expect a stable mid-supply voltage; for digital sensors check for valid messages on the SRS bus.
  6. Inspect and test continuity of each wire from the sensor connector to the airbag control module and for shorts to chassis or battery.
  7. Repair any damaged wiring, corroded connectors, or poor grounds found. Replace the FR impact sensor if its output is out of specification or intermittent when wiring is confirmed good.
  8. After repairs, clear codes and perform built-in self-tests or SRS system checks with scan tool. Confirm B1B71 does not return and that SRS lamp behaves normally.
  9. If problem persists after replacing sensor and wiring repair, suspect airbag control module fault and follow OEM module testing/repair replacement procedures.

Likely causes

  • Corroded connector at FR impact sensor or harness damage near wheelwell/front bumper
  • Wire chafing causing intermittent short to ground or battery
  • Sensor failed due to impact, moisture or age
  • Improperly reinstalled sensor after body repair
  • Faulty SRS module electronics (verify after wiring/sensor checks)

Fault status

⚠️ Status
Front-right impact sensor circuit fault detected by airbag control module. Possible open, short, sensor failure, or connector/wiring problem. Inspect sensor, wiring, and module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

B1B70 B1B72 B1A71 B1B30 B0100
406

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