Code
B150E86
VOLVO
B — Body
Defog Sensor. Signal Invalid
Views:
UK: 14
EN: 17
RU: 16
AI status
Completed
Completed
100%
Causes
- Defog sensor failed or internal fault
- Open, short or high resistance in sensor wiring
- Corroded, loose or damaged sensor connector
- Poor ground or low supply voltage to sensor
- Water ingress or contamination of sensor
- Faulty climate control / body control module or software error
Symptoms
- Climate control/automatic defog not operating as expected
- Defog/warning message or fault indicator displayed in HVAC or instrument cluster
- Intermittent operation of AC blower or heating when defog requested
- Freeze-frame or stored fault in body/climate control module
What to check
- Read fault code and freeze‑frame data with a compatible Volvo scan tool; clear and recheck
- Monitor live sensor data (voltage/resistance/frequency) while changing cabin conditions (breath, mist)
- Visually inspect sensor, connector and harness for corrosion, damage, water intrusion or loose pins
- Check relevant fuses and power/ground circuits for proper voltage and continuity
- Perform wiggle test on harness while monitoring live data for intermittent faults
- Compare measured signal values to service manual reference values
Signal parameters
- Sensor signal typically a low‑voltage analog or digital value — check service manual for exact expected range
- Expect a signal that changes with humidity/condensation conditions; an unchanging or out‑of‑range value indicates a fault
- Voltage range commonly 0–5 V for analog sensors; resistance or frequency values (if applicable) also used — verify with factory data
Diagnostic algorithm
- Connect Volvo‑compatible diagnostic tool; record B150E86 occurrence, freeze‑frame and live data. 2) Clear the code, then attempt to reproduce; note if code returns immediately or intermittently. 3) Visually inspect sensor and connector for corrosion, water or damage; disconnect connector and inspect pins. 4) With ignition on, backprobe sensor connector and verify supply voltage and ground per service data. 5) Measure sensor output (voltage/resistance/frequency) while inducing fogging conditions (breath on windshield or change humidity) to confirm response. 6) If wiring or connector problems found, repair/replace damaged wiring and secure connectors; then retest. 7) If wiring and power/ground OK but output is out of range or unresponsive, replace the defog sensor. 8) If sensor and wiring are good but fault persists, check climate control/body control module for updates, reprogramming, or internal fault and consider module repair or replacement. 9) After repairs, clear codes and verify system operation over drive cycle.
Likely causes
- Connector corrosion or poor pin contact at the defog sensor
- Damaged wiring harness (pinch, chafe, rodent) causing intermittent/open/short
- Sensor failed due to moisture or age
- Ground/return circuit high resistance
- Module receiving implausible signal because of power supply issue
Fault status
Status
Defog sensor signal invalid — signal out of range or intermittent. Inspect sensor, wiring/connectors, power/ground and module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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