P017B

What it means

P017B is a generic code meaning the engine control unit has judged the signal from cylinder head temperature sensor A to be out of its expected range or not plausible. The ECU typically compares the reported head temperature against modelled temperature, coolant temperature, engine load and time since start, and sets the code when they disagree or the reading is stuck or slow to change. Which sensor is 'A' and where it sits depends on the engine, so check the manufacturer data for your model.

Symptoms

• Engine management warning light on
• Temperature readings that look wrong or stay fixed on a scan tool
• Poor performance or reduced power if the ECU enters a protective strategy
• Cooling fan running more than usual or at odd times
• Hard starting or rough running when cold on some engines
• Slightly higher fuel consumption

Possible causes

• Faulty cylinder head temperature sensor giving a drifting, stuck or slow responselikely
• Damaged wiring, chafing or corrosion in the sensor circuit causing high resistance or intermittent signallikely
• Poor connector contact, water ingress or loose terminals at the sensor or ECUlikely
• Cooling system problem such as low coolant, air in the system, or a sticking thermostat causing real temperatures to differ from expectedpossible
• Coolant temperature sensor fault, which makes the head temperature reading look implausible by comparisonpossible
• Overheating history or head gasket issue changing true head temperature behaviourrare
• Faulty ECU or outdated software where a known fault exists for that modelrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine temperature, load and mileage when the code set, and check for related coolant temperature or thermostat codes
2. Check coolant level and condition when the engine is cold, and look for leaks or signs of air in the system
3. Inspect the sensor, its wiring and connectors for damage, heat damage, corrosion, water or loose pins
4. Compare live cylinder head temperature with coolant temperature on a cold engine after it has stood overnight; they should be close
5. Watch live data as the engine warms up and check the head temperature rises smoothly and plausibly, without jumps or sticking
6. Check the sensor circuit for supply, signal, earth, continuity and shorts using the manufacturer's wiring diagram and specified values
7. Test the sensor resistance against the manufacturer's temperature chart, as the values vary by model
8. Check the thermostat and cooling fan operation, and look for any applicable manufacturer bulletins or software updates for the model

How to fix

• Replace the cylinder head temperature sensor if it is out of specification or responds incorrectly
• Repair or replace damaged wiring and clean or renew faulty connectors and terminals
• Correct any cooling system fault, such as topping up and bleeding the system, or replacing a faulty thermostat
• Replace the coolant temperature sensor if it is found to be giving a wrong reading
• Where a known software fault exists for the model, apply the manufacturer's updated calibration
• Clear the code after repair and road test to confirm it does not return

Can I keep driving?

Nearby codes

• P017AGenericCylinder Head Temperature Sensor A Circuit
• P017CGenericCylinder Head Temperature Sensor A Circuit Low