B2381

Code

Other B — Body

Heater Coolant Temp sensor circuit Open

Brand: Other

Type: B — Body

Views: UK: 22 EN: 34 RU: 23

AI status

Completed

ready

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Page language: EN

Causes

Open or broken wiring in the sensor circuit
Disconnected or corroded connector at the sensor or module
Faulty heater coolant temperature sensor (open internally)
Water intrusion or corrosion in connector or sensor
Poor ground or power supply issue to the sensing circuit
Faulty HVAC/body control module (rare)

Symptoms

HVAC system shows incorrect or no heater coolant temperature reading
Reduced or no cabin heat control accuracy
HVAC control may display fault or enter limp mode for temperature control
Diagnostic trouble code stored; possible related HVAC warning lights or messages
No obvious engine overheating indication (code is body-related)

What to check

Retrieve freeze frame and confirm B2381 is current or historical
Visually inspect sensor connector and wiring for damage, corrosion, or disconnection
With key off, disconnect sensor and inspect pins for corrosion and bending
Check continuity between sensor connector and HVAC/body control module connector; look for open circuit
Measure sensor resistance at ambient temperature and while warming/cooling (if accessible) to confirm thermistor behaviour
Probe circuit with key on to measure reference voltage or pull-up voltage at the sensor connector (compare with expected range)

Signal parameters

Sensor type: typically NTC thermistor (resistance decreases as temperature increases)
Open-circuit detection: very high or infinite resistance, or no return voltage to module
Voltage signal (if used): typically a low-voltage signal referenced to module pull-up (varies by manufacturer, commonly 0.1–4.9 V depending on coolant temperature)
Expected behaviour: measured resistance should change smoothly with temperature; abrupt infinite resistance indicates open circuit

Diagnostic algorithm

Verify code and conditions: clear codes, run vehicle to reproduce B2381. Note when code sets (key on, engine running, HVAC on).
Visual inspection: inspect wiring from sensor to HVAC/body control module, connectors, and nearby harness for damage or corrosion. Repair obvious issues.
Check connector and terminals: unplug sensor, inspect and clean pins; reseat firmly.
Resistance test: with sensor disconnected, measure sensor resistance across terminals while varying temperature (warm/cool) if possible. Confirm resistance changes; open or infinite resistance indicates failed sensor.
Circuit continuity: backprobe connector at module and sensor; check continuity to confirm no open between module and sensor connector. Repair broken wiring as needed.
Voltage test: with ignition on, backprobe sensor connector to verify reference/pull-up voltage from module and correct signal behavior as coolant temperature changes.
Wiggle/road test: with scanner monitoring live data, wiggle harness and connectors to detect intermittent opens and re-run test to confirm repair.
Repair and retest: repair or replace faulty sensor, connector, or wiring; clear codes and verify code does not return after operation under conditions that previously set the code.
If wiring and sensor check OK and problem persists, test/replace HVAC/body control module following manufacturer procedures.

Likely causes

Damaged chafe-through wiring harness near firewall or heater core
Loose or unplugged sensor connector at heater hose or heater housing
Sensor element failed (open thermistor)
Corroded pins causing intermittent open circuit

Fault status

⚠️ Status

Circuit indicates open (no continuity) in heater coolant temperature sensor wiring. Sensor/connector/wiring likely failed or disconnected; module not receiving valid temperature signal.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2 hours