P2C3A

Code

Generic P — Powertrain

Cylinder Head Temperature Sensor B Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 33 RU: 21

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Page language: EN

Causes

Short to ground in the sensor B signal wire
Open, corroded, or loose connector at the sensor or ECM
Failed Cylinder Head Temperature (CHT) Sensor B (thermistor shorted or internal fault)
High-resistance connection or damaged wiring (chafing, pinched harness)
Poor or missing reference voltage/ground at the sensor or ECM input
ECM input circuit failure or software/calibration fault

Symptoms

Malfunction Indicator Lamp (MIL/CEL) illuminated with P2C3A stored
Incorrect engine coolant/temperature readings in scan tool (very low or near zero)
Extended engine warm-up, incorrect fuel trim or idle behavior
Cooling fan or temperature-dependent systems may not operate correctly
Possible degraded driveability, increased emissions or poor fuel economy under some conditions

What to check

Scan for freeze-frame and stored related codes; note conditions when the code set (engine temp, load, ignition on, etc.)
Use a scan tool to view live CHT sensor B data and compare to sensor A (if present) and to ambient/expected values
Visually inspect sensor B connector and wiring for corrosion, damage, pin push-out, contamination, or chafing — pay attention to locations near the cylinder head and firewall
Backprobe the sensor connector with engine off; check for proper reference voltage and ground per manufacturer specs
Measure signal voltage with engine at key temperatures (cold ambient and warmed up) and compare to expected ranges; low/near-zero indicates short to ground
Measure sensor resistance at the sensor (cold) and compare to expected thermistor resistance trend (resistance should decrease as temperature rises)

Signal parameters

Typical sensor type: NTC thermistor (resistance decreases as temperature rises)
Common voltage behavior (varies by vehicle): signal normally in 0.2–4.8 V range depending on temperature; a circuit-low condition is typically
Reference voltage often provided or pulled-up by ECM (commonly ~5 V or internal pull-up) — verify with manufacturer data
Approximate resistance guidance (examples only): ~2–3 kΩ at ~25°C, a few hundred ohms at normal operating temperature; values vary by sensor design — compare with OEM specifications

Diagnostic algorithm

Retrieve freeze-frame data and confirm the fault conditions (temperature, engine speed, load). Note whether the code is intermittent or continuous.
Visually inspect sensor B connector and harness for damage, contamination, or loosened pins. Repair any obvious connector or wiring damage.
With the ignition ON (engine off), backprobe the sensor connector: verify reference voltage (if present) and ground at the connector. If reference or ground missing, trace to ECM.
Measure signal voltage at the sensor connector with engine cold and after warm-up. If voltage is near zero or abnormally low, suspect short to ground or bad sensor.
Unplug the sensor and measure resistance across sensor terminals at ambient temperature. Compare to OEM chart or expected thermistor behavior (resistance should be finite and change with temperature).
If sensor resistance is normal but signal stays low with sensor connected, check continuity of the signal wire to the ECM and test for short to ground (measure resistance between signal wire and chassis ground with power disconnected).
If a short to ground is found: isolate the short by sectioning the harness or disconnecting connectors until the short disappears; repair or replace damaged wiring or connectors.
If wiring and connector checks are good and sensor resistance is abnormal, replace CHT Sensor B and retest.
If wiring, connector, and replacement sensor still show low signal, inspect ECM input and grounds; consult manufacturer diagnostics for ECM testing or replacement.
Clear codes, perform a test drive or run necessary drive cycles and re-scan to confirm repair. Document any intermittent behavior for further tracing.

Likely causes

Damaged or shorted signal wire between sensor B and ECM
Corroded/loose connector at the sensor or cylinder head harness
Failed CHT Sensor B (thermistor short or internal failure)
Faulty ground or reference circuit at the ECM
ECM input stage fault (least likely)

Fault status

⚠️ Status

DTC P2C3A set when Cylinder Head Temperature Sensor B signal is detected below the allowed threshold (circuit low), indicating a circuit short/low-voltage condition or sensor fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours