P1285
Cylinder Head Temperature Sensor Out of Self-Test Range
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The P1285 is a Ford-specific code indicating that the Cylinder Head Temperature (CHT) sensor reading was outside the expected range during the PCM's self-test. Ford uses a CHT sensor instead of a traditional coolant temperature sensor on many engines. This sensor is threaded into the cylinder head and provides critical temperature data that the PCM uses for fuel injection timing, cooling fan operation, and overheat protection.
When this code appears, the most likely cause is a failed CHT sensor itself. These sensors can degrade over time, providing inaccurate readings. However, it's important to first rule out an actual overheating condition — check your coolant level, look for leaks, and verify the cooling fans are operating correctly. If the temperature gauge reads abnormally (either stuck cold or pegged hot), the sensor or its wiring is the probable culprit.
The CHT sensor is located in the cylinder head, often beneath the intake manifold, which can make access somewhat difficult depending on the engine. The sensor itself is inexpensive ($15–$40), but labor to access it can be significant on some models. If you notice the engine actually overheating (steam, sweet coolant smell, gauge in the red), stop driving immediately and address the cooling system before worrying about the sensor.
Severity
Symptoms
- •Check engine light is on
- •Temperature gauge reads abnormally high or low
- •Engine may enter reduced power (limp) mode
- •Cooling fans may run at full speed constantly
- •Air conditioning compressor may not engage
Likely Causes
The CHT sensor can fail internally, providing incorrect resistance values that translate to inaccurate temperature readings outside the expected range.
Corroded, broken, or shorted wiring between the CHT sensor and the PCM can cause voltage readings outside the normal self-test range.
A real overheating problem caused by low coolant, a failed thermostat, or a bad water pump can push temperature readings out of the self-test range.
The PCM's input port for the CHT sensor signal may have a fault causing it to misread the sensor voltage.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the cylinder head temperature (CHT) sensor
- Repair or replace corroded wiring and connectors at the CHT sensor
- Check coolant level and inspect the cooling system for leaks
- Verify thermostat operation and replace if stuck