P2C3D

Code

Generic P — Powertrain

Cylinder Head Temperature Sensor A/B Correlation

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 43 RU: 21

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

One or both CHT sensors failed or out of specification
Open, shorted or corroded wiring/connectors between sensors and ECU
Shared reference/ground fault (poor ground or reference voltage)
Air pocket, coolant flow restriction, leaking head gasket or localized cooling issue causing true temperature difference
Thermostat stuck open/closed or coolant flow problem
Intermittent connector contact (moisture, corrosion) or chafed harness

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Engine temperature gauge or temperature readout is erratic or inconsistent
Long warm-up time or engine running colder/warmer than expected
Potential reduced engine performance or limp-home strategy on some vehicles
Possible rough idle, poor fuel economy or incorrect fuel trim if ECU uses CHT for calibration
Cooling fan operation may be incorrect or intermittent

What to check

Read freeze frame and all stored codes with a capable scan tool; note raw CHT A and CHT B values and any pending codes
Compare live stream of CHT A vs CHT B at key conditions: cold start, after warm-up, under load and at idle
Inspect sensor connectors and wiring for corrosion, bent pins, damage, rubbing or melting
Measure sensor resistances at known temperatures (room/cold/hot) and compare to spec or between sensors
Backprobe sensor signal and reference circuits to check for proper reference voltage and signal behavior
Check continuity from each sensor to the ECU pin and for unintended cross-connections between sensor circuits

Signal parameters

Sensor type: typically NTC thermistor (resistance decreases as temperature rises)
Typical resistance ballpark: ~2–4 kΩ at ~20–25°C, falling toward a few hundred ohms at high coolant temperatures (values vary by vehicle; consult OEM specs)
Typical voltage signal range (sensor-to-ECU) across operating temperature: approx. 0.1–4.9 V depending on design and ECU pull-up/reference
Expected correlation: both CHT sensors should track closely — generally within about 5–10°C (≈9–18°F) or a small fraction of a volt under similar conditions; ECU trigger threshold may be larger (manufacturer dependent)
Response time: both sensors should change in similar slope when temperature changes (no long delay in one sensor)

Diagnostic algorithm

Use a scan tool to record live CHT A and CHT B values at cold start, idle after warm-up, and during a short road drive. Note the magnitude and conditions of the difference.
Inspect both sensor connectors for corrosion, bent pins, moisture ingress, and secure fit. Repair or replace connectors as needed.
Visually inspect wiring harness along routing for chafing, heat damage or repairs. Repair any damaged sections and restore proper routing/clips.
With ignition off, disconnect each sensor and measure resistance to confirm each sensor responds to temperature. If one sensor is out of expected range or open, replace the sensor.
Backprobe signal and ground/reference with engine running (or during warm-up) to verify each sensor circuit has proper reference voltage and that signal varies as temperature changes. Look for open, short to voltage/ground, or swapped signals.
Check continuity from each sensor connector to the ECU pin and confirm no cross-talk between A and B circuits. Repair wiring faults and re-pin connectors if necessary.
If wiring and sensors check good but correlation is still poor, inspect cooling system for trapped air, thermostat operation, water pump function, blockages or head gasket leaks that could cause localized overheating.
If available and safe, swap the two sensors (if identical) and see if the code follows the sensor; this helps distinguish sensor vs harness/ECU issue.
If no wiring or sensor faults are found and cooling system is normal, consider ECU input fault; confirm with wiring checks and consult manufacturer service info before replacing ECU.
After repairs, clear codes and perform a warm-up/drive cycle to verify CHT A/B correlation returns to normal and code does not reset.

Likely causes

Sensor A or B has internal fault (NTC drift or open circuit)
Damaged harness between sensor and ECU (short-to-ground or to other sensor)
Connector corrosion or poor pin contact at sensor or ECU
Cooling system issue creating real temperature difference (blockage, trapped air)
Faulty thermostat or water pump reducing flow and causing uneven temps

Fault status

⚠️ Status

Cylinder Head Temperature Sensor A/B Correlation — The PCM/ECM detected an unacceptable difference between the readings of the two cylinder head temperature sensors. Check sensors, wiring, connectors, cooling system and PCM inputs.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours