Code
B1257
ALFA ROMEO
B — Body
External air temperature sensor short to ground
Views:
UK: 5
EN: 7
RU: 8
AI status
Completed
Completed
100%
Causes
- Short circuit in the sensor signal wire to ground
- Damaged or chafed wiring harness contacting chassis ground
- Corroded or bent connector pins causing low-resistance path to ground
- Failed ambient/external air temperature sensor (internal short)
- Water ingress in connector or sensor body
- Incorrect installation or aftermarket sensor with wrong wiring
Symptoms
- Ambient temperature display shows incorrect or fixed very low value
- Climate control/AC automatic functions behaving incorrectly
- Rear or exterior temperature readout erratic or fluctuating
- Associated HVAC or body control warning light or message (depends on vehicle)
- DTC/BMS stored and possibly preventing certain climate features
What to check
- Retrieve codes and freeze-frame data with a scan tool; confirm B1257 is current
- Monitor live ambient temperature sensor reading and compare to actual ambient temp
- Visually inspect sensor, connector and wiring for damage, corrosion, or water
- Back-probe sensor connector and measure signal voltage with key on
- Check continuity from sensor signal pin to chassis ground with connector disconnected
- Measure sensor resistance at ambient and compare to expected thermistor behavior (resistance changes with temperature)
Signal parameters
- Type: typically NTC thermistor (resistance decreases as temperature rises)
- Expected behavior: signal value should change smoothly with ambient temperature
- Short-to-ground symptom: signal voltage near 0 V or resistance reading indicating low-ohm path to ground
- Open-circuit symptom (for reference): high resistance or infinite ohms
Diagnostic algorithm
- Confirm code: read stored/active B1257 and note freeze-frame/live data.
- Observe ambient temp reading on scan tool and compare to actual outside temperature (thermometer).
- Visually inspect sensor location (usually front bumper area or mirror), connector and harness for obvious damage or moisture.
- With ignition ON, back-probe the sensor signal wire and measure voltage. If near 0 V, suspect short to ground.
- Disconnect sensor from harness. Measure resistance from signal pin to chassis ground; a low value indicates a short in the harness. Also measure sensor resistance to verify sensor integrity.
- Perform wiggle test on harness while monitoring signal for intermittent shorts; repair any chafing or pin damage found.
- If harness wiring is intact, replace the sensor and re-test. If replacement sensor still shows short, trace and repair wiring back to the control module.
- After repair or replacement, clear codes, perform functional test and verify that ambient temperature reading responds correctly and code does not return.
- Check for Technical Service Bulletins (TSBs) or manufacturer-specific wiring diagrams if root cause unclear.
Likely causes
- Broken insulation where the signal wire rubs against a metal edge
- Connector corrosion allowing the signal to bypass into ground
- Sensor element internally shorted due to moisture or manufacturing failure
- Recent repair or work in the area that disturbed the harness or connector
Fault status
Status
External air temperature sensor circuit short to ground — ambient temperature sensor signal is being pulled to ground. Inspect sensor, connector and wiring for short to chassis ground.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
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Code
B1257
FIAT
B — Body
External air temperature sensor short to ground
Views:
UK: 5
EN: 6
RU: 8
AI status
Completed
Completed
100%
Causes
- Short circuit in the sensor signal wire to ground
- Damaged or chafed wiring harness contacting chassis ground
- Corroded or bent connector pins causing low-resistance path to ground
- Failed ambient/external air temperature sensor (internal short)
- Water ingress in connector or sensor body
- Incorrect installation or aftermarket sensor with wrong wiring
Symptoms
- Ambient temperature display shows incorrect or fixed very low value
- Climate control/AC automatic functions behaving incorrectly
- Rear or exterior temperature readout erratic or fluctuating
- Associated HVAC or body control warning light or message (depends on vehicle)
- DTC/BMS stored and possibly preventing certain climate features
What to check
- Retrieve codes and freeze-frame data with a scan tool; confirm B1257 is current
- Monitor live ambient temperature sensor reading and compare to actual ambient temp
- Visually inspect sensor, connector and wiring for damage, corrosion, or water
- Back-probe sensor connector and measure signal voltage with key on
- Check continuity from sensor signal pin to chassis ground with connector disconnected
- Measure sensor resistance at ambient and compare to expected thermistor behavior (resistance changes with temperature)
Signal parameters
- Type: typically NTC thermistor (resistance decreases as temperature rises)
- Expected behavior: signal value should change smoothly with ambient temperature
- Short-to-ground symptom: signal voltage near 0 V or resistance reading indicating low-ohm path to ground
- Open-circuit symptom (for reference): high resistance or infinite ohms
Diagnostic algorithm
- Confirm code: read stored/active B1257 and note freeze-frame/live data.
- Observe ambient temp reading on scan tool and compare to actual outside temperature (thermometer).
- Visually inspect sensor location (usually front bumper area or mirror), connector and harness for obvious damage or moisture.
- With ignition ON, back-probe the sensor signal wire and measure voltage. If near 0 V, suspect short to ground.
- Disconnect sensor from harness. Measure resistance from signal pin to chassis ground; a low value indicates a short in the harness. Also measure sensor resistance to verify sensor integrity.
- Perform wiggle test on harness while monitoring signal for intermittent shorts; repair any chafing or pin damage found.
- If harness wiring is intact, replace the sensor and re-test. If replacement sensor still shows short, trace and repair wiring back to the control module.
- After repair or replacement, clear codes, perform functional test and verify that ambient temperature reading responds correctly and code does not return.
- Check for Technical Service Bulletins (TSBs) or manufacturer-specific wiring diagrams if root cause unclear.
Likely causes
- Broken insulation where the signal wire rubs against a metal edge
- Connector corrosion allowing the signal to bypass into ground
- Sensor element internally shorted due to moisture or manufacturing failure
- Recent repair or work in the area that disturbed the harness or connector
Fault status
Status
External air temperature sensor circuit short to ground — ambient temperature sensor signal is being pulled to ground. Inspect sensor, connector and wiring for short to chassis ground.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
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Code
B1257
LAND ROVER
B — Body
Ambient air temperature sensor - short circuit to ground Solar radiation sensor - circuit failure circuit open Left rear visor
Views:
UK: 5
EN: 9
RU: 9
AI status
Completed
Completed
100%
Causes
- Short circuit in the sensor signal wire to ground
- Damaged or chafed wiring harness contacting chassis ground
- Corroded or bent connector pins causing low-resistance path to ground
- Failed ambient/external air temperature sensor (internal short)
- Water ingress in connector or sensor body
- Incorrect installation or aftermarket sensor with wrong wiring
Symptoms
- Ambient temperature display shows incorrect or fixed very low value
- Climate control/AC automatic functions behaving incorrectly
- Rear or exterior temperature readout erratic or fluctuating
- Associated HVAC or body control warning light or message (depends on vehicle)
- DTC/BMS stored and possibly preventing certain climate features
What to check
- Retrieve codes and freeze-frame data with a scan tool; confirm B1257 is current
- Monitor live ambient temperature sensor reading and compare to actual ambient temp
- Visually inspect sensor, connector and wiring for damage, corrosion, or water
- Back-probe sensor connector and measure signal voltage with key on
- Check continuity from sensor signal pin to chassis ground with connector disconnected
- Measure sensor resistance at ambient and compare to expected thermistor behavior (resistance changes with temperature)
Signal parameters
- Type: typically NTC thermistor (resistance decreases as temperature rises)
- Expected behavior: signal value should change smoothly with ambient temperature
- Short-to-ground symptom: signal voltage near 0 V or resistance reading indicating low-ohm path to ground
- Open-circuit symptom (for reference): high resistance or infinite ohms
Diagnostic algorithm
- Confirm code: read stored/active B1257 and note freeze-frame/live data.
- Observe ambient temp reading on scan tool and compare to actual outside temperature (thermometer).
- Visually inspect sensor location (usually front bumper area or mirror), connector and harness for obvious damage or moisture.
- With ignition ON, back-probe the sensor signal wire and measure voltage. If near 0 V, suspect short to ground.
- Disconnect sensor from harness. Measure resistance from signal pin to chassis ground; a low value indicates a short in the harness. Also measure sensor resistance to verify sensor integrity.
- Perform wiggle test on harness while monitoring signal for intermittent shorts; repair any chafing or pin damage found.
- If harness wiring is intact, replace the sensor and re-test. If replacement sensor still shows short, trace and repair wiring back to the control module.
- After repair or replacement, clear codes, perform functional test and verify that ambient temperature reading responds correctly and code does not return.
- Check for Technical Service Bulletins (TSBs) or manufacturer-specific wiring diagrams if root cause unclear.
Likely causes
- Broken insulation where the signal wire rubs against a metal edge
- Connector corrosion allowing the signal to bypass into ground
- Sensor element internally shorted due to moisture or manufacturing failure
- Recent repair or work in the area that disturbed the harness or connector
Fault status
Status
External air temperature sensor circuit short to ground — ambient temperature sensor signal is being pulled to ground. Inspect sensor, connector and wiring for short to chassis ground.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
2
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualOfficial workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.
199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualWorkshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.
199,00 UAH
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
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Send to email
Code
B1257
Other
B — Body
Air Temperature External Sensor Circuit Short To Ground
Views:
UK: 13
EN: 31
RU: 21
AI status
Completed
Completed
100%
Causes
- Short circuit in the sensor signal wire to ground
- Damaged or chafed wiring harness contacting chassis ground
- Corroded or bent connector pins causing low-resistance path to ground
- Failed ambient/external air temperature sensor (internal short)
- Water ingress in connector or sensor body
- Incorrect installation or aftermarket sensor with wrong wiring
Symptoms
- Ambient temperature display shows incorrect or fixed very low value
- Climate control/AC automatic functions behaving incorrectly
- Rear or exterior temperature readout erratic or fluctuating
- Associated HVAC or body control warning light or message (depends on vehicle)
- DTC/BMS stored and possibly preventing certain climate features
What to check
- Retrieve codes and freeze-frame data with a scan tool; confirm B1257 is current
- Monitor live ambient temperature sensor reading and compare to actual ambient temp
- Visually inspect sensor, connector and wiring for damage, corrosion, or water
- Back-probe sensor connector and measure signal voltage with key on
- Check continuity from sensor signal pin to chassis ground with connector disconnected
- Measure sensor resistance at ambient and compare to expected thermistor behavior (resistance changes with temperature)
Signal parameters
- Type: typically NTC thermistor (resistance decreases as temperature rises)
- Expected behavior: signal value should change smoothly with ambient temperature
- Short-to-ground symptom: signal voltage near 0 V or resistance reading indicating low-ohm path to ground
- Open-circuit symptom (for reference): high resistance or infinite ohms
Diagnostic algorithm
- Confirm code: read stored/active B1257 and note freeze-frame/live data.
- Observe ambient temp reading on scan tool and compare to actual outside temperature (thermometer).
- Visually inspect sensor location (usually front bumper area or mirror), connector and harness for obvious damage or moisture.
- With ignition ON, back-probe the sensor signal wire and measure voltage. If near 0 V, suspect short to ground.
- Disconnect sensor from harness. Measure resistance from signal pin to chassis ground; a low value indicates a short in the harness. Also measure sensor resistance to verify sensor integrity.
- Perform wiggle test on harness while monitoring signal for intermittent shorts; repair any chafing or pin damage found.
- If harness wiring is intact, replace the sensor and re-test. If replacement sensor still shows short, trace and repair wiring back to the control module.
- After repair or replacement, clear codes, perform functional test and verify that ambient temperature reading responds correctly and code does not return.
- Check for Technical Service Bulletins (TSBs) or manufacturer-specific wiring diagrams if root cause unclear.
Likely causes
- Broken insulation where the signal wire rubs against a metal edge
- Connector corrosion allowing the signal to bypass into ground
- Sensor element internally shorted due to moisture or manufacturing failure
- Recent repair or work in the area that disturbed the harness or connector
Fault status
Status
External air temperature sensor circuit short to ground — ambient temperature sensor signal is being pulled to ground. Inspect sensor, connector and wiring for short to chassis ground.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
Similar codes
Workshop Manuals
Available brands with manuals
1
LAND ROVER 2
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualOfficial workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.
199,00 UAH
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualWorkshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.
199,00 UAH
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
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0
👎 Dislike
0
Send to email