P2C3A: Cylinder Head Temperature Sensor B Circuit Low

What it means

The ECM detects a circuit low fault on the cylinder head temperature sensor b circuit. Reading cannot be used reliably for control.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

Cylinder head temperature sensor B measures temperature at its location on the cylinder head and sends a signal to the ECM. The ECM sets this code when the B circuit reads lower than expected, so it cannot rely on that temperature signal for control.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Internal sensor short
3. Connector pins corroded - high contact resistance

Symptoms

• Check-engine light
• Engine temperature reading may be inaccurate
• Hard starting

How to diagnose it

1. Review freeze-frame data and compare sensor B's live temperature reading with sensor A and the engine's cold-soak temperature to see whether B is implausibly low.
2. Inspect sensor B's connector and harness for corrosion, damaged insulation, or a signal wire touching ground.
3. Check the connector pins for corrosion or poor contact that could disrupt the sensor B signal.
4. With the circuit isolated as specified by the manufacturer, test sensor B and its signal wire for a short to ground.
5. Compare sensor B resistance or output with the manufacturer's specification and replace the sensor if it is internally shorted.

Common fixes

• Clean or repair corroded sensor B connector pins and restore a secure connection.
• Repair the sensor B signal wire where it is shorted to ground.
• Replace cylinder head temperature sensor B if it fails the manufacturer's test.

Can I keep driving?

If the temperature reading is inaccurate or the engine is hard to start, avoid heavy loads and watch the temperature gauge closely. Stop safely if the engine overheats; an unreliable reading can hide a real overheating condition.