P2C39

Code

Generic P — Powertrain

Cylinder Head Temperature Sensor B Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 42 RU: 25

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Faulty cylinder head temperature sensor B (open, shorted or out of spec)
Damaged, corroded, or loose connector at the sensor
Wiring harness damage (open, short to battery, short to ground, high resistance)
Poor sensor reference ground or ECM ground issue
Intermittent connector contact or water intrusion
Engine coolant level, thermostat, or head cooling passages causing unexpected temperatures

Malfunction Indicator Lamp (MIL)/Check Engine Light illuminated
Incorrect temperature readings in live data for cylinder head temp B vs sensor A or engine coolant temp
Cold/hot start issues or abnormal idle/fueling if ECU uses CHT for control
Reduced performance or limp-home mode on some vehicles if ECU relies on CHT
Possible reduced fuel economy or delayed fan operation

Read and record freeze-frame and live data for CHT sensor B, CHT sensor A (if present), and engine coolant temperature (ECT)
Check for additional related DTCs (ECT sensor codes P0115/P0117/P0118 or other CHT codes)
Visual inspection of the sensor, connector, and wiring for corrosion, damage, or coolant contamination
Backprobe connector with engine running to observe sensor signal and reference voltage/ground
Measure sensor resistance (with sensor removed/cool) and compare to specification or to the known-good sensor if available
Perform wiggle test on wiring while monitoring live data to check for intermittent faults

Most CHT sensors are thermistor-type (NTC): resistance decreases as temperature rises
ECM typically expects a 0–5 V signal (or specific resistance curve) corresponding to temperature; consult vehicle service data for exact curve
At cold ambient temps sensor resistance is relatively high; at operating temp resistance is lower — compare to spec chart
Typical diagnostics use resistance vs. temperature chart or live voltage reading to verify sensor behavior

Connect a scan tool and capture freeze frame and live data for CHT sensor B plus ECT/CHT A. Note temperatures at key conditions (cold start, warm idle).
If code is current, attempt a quick re-test: clear code, reproduce conditions, and see if code returns to confirm repeatability.
Visually inspect sensor and connector for corrosion, coolant residue, crushed wires, or poor sealing. Repair any obvious damage.
Backprobe the sensor connector: verify reference voltage (if present), signal voltage, and ground continuity to the ECM. Compare to specifications.
Remove the sensor and measure resistance at a known ambient temperature. If possible, gently heat the sensor (hot water) and observe resistance change — it should change smoothly per thermistor behavior. Compare to spec or to a known-good sensor.
Perform continuity checks and insulation/short tests on harness between sensor and ECM (check for short to power or ground).
If wiring and grounds are good but readings remain out of range, replace the sensor with a known-good unit and re-test.
After repair, clear codes and road test to verify the code does not return and that temperature readings are plausible. Re-check freeze frame if necessary.
If problem persists and wiring/sensor tests are good, consider ECM input circuit diagnosis or consult manufacturer-specific technical service information.