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Home / DTC / B1B71 — Evaporator temperature sensor

B1B71 — Evaporator temperature sensor

Detailed page for trouble code B1B71.

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22,461specific
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B1B71

LAND ROVER B — Body

Evaporator temperature sensor

Brand: LAND ROVER
Type: B — Body
Views: UK: 11 EN: 29 RU: 23
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted evaporator temperature sensor (thermistor).
  • Corroded, loose or contaminated sensor connector or wiring harness.
  • Water ingress or physical damage to sensor or harness near the evaporator.
  • Sensor contaminated, covered, or mispositioned (not exposed to evaporator airflow).
  • Faulty HVAC/BCM control module or incorrect reference/pull‑up voltage.
  • Intermittent wiring fault (pinched, chafed, or broken wires).

Symptoms

  • HVAC shows incorrect evaporator temperature or unrealistic temperature reading in live data.
  • A/C cycles rapidly or compressor disabled to prevent evaporator freeze.
  • Reduced or no cooling, or unexpected blower/A/C behavior.
  • DTC stored or warning message displayed on cluster/infotainment.
  • Intermittent A/C operation or erratic temperature control.

What to check

  • Read and record freeze frame and freeze/fault count with compatible scan tool, then clear and re‑check.
  • Inspect sensor connector at evaporator for corrosion, pin damage, water ingress, or bent pins.
  • Visually inspect wiring harness along the route to the HVAC module for chafing, breaks, or repairs.
  • Use scan tool to view live evaporator temperature values and compare to ambient cabin temp.
  • Measure sensor resistance at connector (with connector disconnected) and compare to expected thermistor behavior vs ambient temperature.
  • Check for short to power or short to ground on the sensor circuit (backprobe with multimeter).

Signal parameters

  • Sensor type: NTC thermistor (resistance decreases as temperature increases).
  • Typical signal: low voltage analog to HVAC module (often a pull‑up to reference; module measures voltage).
  • Expected electrical behaviour: resistance varies with temperature (example general range: a few kΩ at moderate cabin temps—exact values vary by model).
  • Signal voltage expected within module reference range (commonly 0.5–4.5 V depending on temperature and vehicle wiring).
  • Response: sensor should change resistance/voltage smoothly with temperature; abrupt open/short or frozen value indicates fault.

Diagnostic algorithm

  1. Verify code with a capable scan tool. Note whether code is active or historical and capture live evaporator temp and related HVAC parameters.
  2. Perform a visual inspection of the sensor, connector and harness at the evaporator under the dash/evaporator housing for damage or moisture.
  3. Backprobe the sensor connector and with ignition on, measure reference/pull‑up voltage and signal voltage to the HVAC module. Compare to expected ranges from signal_params.
  4. Disconnect the sensor and measure its resistance with a multimeter at ambient temperature. Confirm resistance changes when warmed/cooled (finger warm, or place in known temperature environment).
  5. Check continuity of the sensor wiring to the HVAC module and check for short to ground or battery using an ohmmeter while disconnected from the module.
  6. If wiring and connector are good but sensor resistance/voltage is out of expected behavior, replace the evaporator temperature sensor.
  7. If sensor and wiring check good, test/replace HVAC control module input/pull‑up circuitry per manufacturer procedures or consult wiring diagrams; consider module swap only after confirming sensor circuit integrity.
  8. After repair, clear codes, run A/C system and monitor live data to confirm proper sensor readings and stable HVAC operation; check for evaporator icing during operation if symptom was freeze.

Likely causes

  • Open or shorted sensor element (most common).
  • Corroded/loose connector at the evaporator (common due to moisture).
  • Wiring short to ground or battery in harness to the HVAC module.
  • Sensor contaminated or incorrectly seated in evaporator housing.
  • Less likely: HVAC module input stage fault.

Fault status

⚠️ Status
Stored fault for evaporator temperature sensor circuit (open/short/intermittent). May cause HVAC to enter failsafe mode or disable compressor to prevent evaporator freeze until condition is resolved.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1B70 B1B72 B1B73 B1451 B1A11
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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Code

B1B71

MITSUBISHI B — Body

FR impact sensor

Brand: MITSUBISHI
Type: B — Body
Views: UK: 20 EN: 41 RU: 35
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted evaporator temperature sensor (thermistor).
  • Corroded, loose or contaminated sensor connector or wiring harness.
  • Water ingress or physical damage to sensor or harness near the evaporator.
  • Sensor contaminated, covered, or mispositioned (not exposed to evaporator airflow).
  • Faulty HVAC/BCM control module or incorrect reference/pull‑up voltage.
  • Intermittent wiring fault (pinched, chafed, or broken wires).

Symptoms

  • HVAC shows incorrect evaporator temperature or unrealistic temperature reading in live data.
  • A/C cycles rapidly or compressor disabled to prevent evaporator freeze.
  • Reduced or no cooling, or unexpected blower/A/C behavior.
  • DTC stored or warning message displayed on cluster/infotainment.
  • Intermittent A/C operation or erratic temperature control.

What to check

  • Read and record freeze frame and freeze/fault count with compatible scan tool, then clear and re‑check.
  • Inspect sensor connector at evaporator for corrosion, pin damage, water ingress, or bent pins.
  • Visually inspect wiring harness along the route to the HVAC module for chafing, breaks, or repairs.
  • Use scan tool to view live evaporator temperature values and compare to ambient cabin temp.
  • Measure sensor resistance at connector (with connector disconnected) and compare to expected thermistor behavior vs ambient temperature.
  • Check for short to power or short to ground on the sensor circuit (backprobe with multimeter).

Signal parameters

  • Sensor type: NTC thermistor (resistance decreases as temperature increases).
  • Typical signal: low voltage analog to HVAC module (often a pull‑up to reference; module measures voltage).
  • Expected electrical behaviour: resistance varies with temperature (example general range: a few kΩ at moderate cabin temps—exact values vary by model).
  • Signal voltage expected within module reference range (commonly 0.5–4.5 V depending on temperature and vehicle wiring).
  • Response: sensor should change resistance/voltage smoothly with temperature; abrupt open/short or frozen value indicates fault.

Diagnostic algorithm

  1. Verify code with a capable scan tool. Note whether code is active or historical and capture live evaporator temp and related HVAC parameters.
  2. Perform a visual inspection of the sensor, connector and harness at the evaporator under the dash/evaporator housing for damage or moisture.
  3. Backprobe the sensor connector and with ignition on, measure reference/pull‑up voltage and signal voltage to the HVAC module. Compare to expected ranges from signal_params.
  4. Disconnect the sensor and measure its resistance with a multimeter at ambient temperature. Confirm resistance changes when warmed/cooled (finger warm, or place in known temperature environment).
  5. Check continuity of the sensor wiring to the HVAC module and check for short to ground or battery using an ohmmeter while disconnected from the module.
  6. If wiring and connector are good but sensor resistance/voltage is out of expected behavior, replace the evaporator temperature sensor.
  7. If sensor and wiring check good, test/replace HVAC control module input/pull‑up circuitry per manufacturer procedures or consult wiring diagrams; consider module swap only after confirming sensor circuit integrity.
  8. After repair, clear codes, run A/C system and monitor live data to confirm proper sensor readings and stable HVAC operation; check for evaporator icing during operation if symptom was freeze.

Likely causes

  • Open or shorted sensor element (most common).
  • Corroded/loose connector at the evaporator (common due to moisture).
  • Wiring short to ground or battery in harness to the HVAC module.
  • Sensor contaminated or incorrectly seated in evaporator housing.
  • Less likely: HVAC module input stage fault.

Fault status

⚠️ Status
Stored fault for evaporator temperature sensor circuit (open/short/intermittent). May cause HVAC to enter failsafe mode or disable compressor to prevent evaporator freeze until condition is resolved.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1B70 B1B72 B1B73 B1451 B1A11
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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