What it means
The control module checks whether cylinder head temperature sensor A reports a plausible temperature as the engine warms and runs. It sets this code when the reading is electrically present but falls outside expected behavior.
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 A reports temperature to the control module on engines that use a cylinder-head sensor rather than a conventional coolant-temperature sensor. P017B sets when the signal is present but sensor A’s reported temperature does not behave plausibly as the engine warms or runs.
Common causes
Most likely first.
- Sensor reading drifted
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check engine light on
- Temperature gauge or warning may behave abnormally
- Hard starting or rough running
- Reduced engine performance
How to diagnose it
- Check freeze-frame data and compare sensor A’s cold reading with ambient temperature and its live reading during warm-up.
- Inspect sensor A’s mounting and connector for looseness, poor seating, corrosion, or damaged wiring that could distort the reading.
- Watch live data through a warm-up cycle for sudden jumps, a reading that barely changes, or a response that conflicts with engine behavior.
- Check the sensor circuit for intermittent connections and compare sensor resistance or signal with the manufacturer's specification.
- If the circuit and mounting are sound, test cylinder head temperature sensor A for drift or a slow response.
Common fixes
- Secure sensor A if its mounting is loose.
- Repair poor connector contact or damaged wiring affecting the reading.
- Replace cylinder head temperature sensor A if its reading drifts or responds incorrectly in testing.
Can I keep driving?
A short, cautious drive may be possible if the temperature indication is credible and there are no overheating signs. Stop if a temperature warning appears, since a misleading reading can hide overheating or disrupt engine operation.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.