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P1299 — Cylinder Head Overtemperature Protection Active

Manufacturer-specificPowertrain (engine & transmission)

P1299 indicates that the engine control module has detected an excessively high cylinder head temperature and has activated a protection strategy to prevent damage. This typically results in reduced engine power or a fail-safe cooling mode.

Symptoms

What causes it — most likely first

1. Faulty cylinder head temperature (CHT) sensor

The CHT sensor itself can fail and report an incorrect high temperature, triggering the protection mode even when the engine is not actually overheating.

2. Low coolant level or coolant leak

Insufficient coolant reduces the system's ability to cool the cylinder head, causing real overheating and setting the code.

3. Stuck-closed thermostat

A thermostat that fails to open prevents coolant from circulating through the radiator, leading to rapid overheating of the cylinder head.

4. Faulty cooling fan or fan relay

If the electric cooling fan does not operate when needed, heat builds up in the engine bay, especially at idle or low speeds, causing high cylinder head temperatures.

5. Wiring or connector issues at CHT sensor

Corroded, damaged, or loose wiring/connectors can cause erratic or false high-resistance readings, mimicking an overtemperature condition.

6. Failed water pump or restricted coolant passages

A water pump with a broken impeller or internal blockage reduces coolant flow, leading to localized hot spots and triggering the protection mode.

How it's diagnosed

  1. Check coolant level and inspect for visible leaks; top off if low and verify system holds pressure.
  2. Use a scan tool to read live CHT sensor data; compare to actual engine temperature (e.g., using an infrared thermometer on the cylinder head near the sensor).
  3. If CHT reading is high but engine is cool, suspect a faulty sensor; test sensor resistance per manufacturer specifications.
  4. Inspect the CHT sensor wiring and connector for damage, corrosion, or poor contact; repair as needed.
  5. Check thermostat operation by monitoring upper radiator hose temperature after warm-up; if hose stays cold, thermostat may be stuck closed.
  6. Verify cooling fan operation by commanding it on with a scan tool or by watching it cycle with A/C on; replace fan or relay if it fails to run.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP1298 — Idm Failure

Frequently asked

Can I continue driving with code P1299?

No. The protection mode is active because the engine computer believes the cylinder head is overheating. Continuing to drive can cause severe engine damage, including warped cylinder heads or blown head gaskets. Have the vehicle diagnosed and repaired promptly.

Is the coolant temperature sensor the same as the cylinder head temperature sensor?

Not always. Some vehicles use a separate CHT sensor mounted in the cylinder head, while others use the engine coolant temperature (ECT) sensor. P1299 specifically refers to the cylinder head temperature sensor. Check your vehicle's service information for the exact location and type.

Do I need to replace the PCM for P1299?

Almost never. The PCM is simply reacting to a high temperature signal. The root cause is almost always a sensor, cooling system, or wiring issue. Replacing the PCM is a last resort only after all other possibilities have been ruled out.

Will clearing the code fix the problem?

No. Clearing the code may temporarily turn off the check engine light, but the underlying issue remains. If the condition is still present, the code will return, often within a few drive cycles.