P1289
Cylinder Head Temperature Sensor Circuit High Input
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The P1289 is a Ford-specific code that is set when the Powertrain Control Module detects a voltage greater than 4.6 volts on the Cylinder Head Temperature sensor circuit. This high voltage typically indicates an open circuit — meaning the electrical connection between the sensor and the PCM is broken somewhere. A telltale sign is the temperature gauge dropping to the very bottom of its range and staying there, even after the engine is fully warmed up.
When the PCM sees this high-voltage condition, it enters a fail-safe mode: cooling fans run at maximum speed, the air conditioning compressor is disabled, and engine power may be reduced. While this protects the engine from potential overheating, it also means the PCM is operating without accurate temperature data, which affects fuel mixture, ignition timing, and emissions.
Diagnosis should start at the CHT sensor connector — look for corrosion, bent pins, or a disconnected plug. The sensor is located in the cylinder head and on some Ford engines requires removal of the intake manifold for access. Test the sensor's resistance with a multimeter (it should change smoothly with temperature). If the wiring and connector are good, replace the sensor. Parts are inexpensive ($15–$40), though labor can vary depending on accessibility.
Severity
Symptoms
- •Temperature gauge drops to the very bottom and does not rise as the engine warms up
- •Check engine light is on
- •Engine enters limp mode with reduced power
- •Cooling fans run on high speed continuously
- •Air conditioning will not engage
Likely Causes
An open wire between the sensor and PCM causes the voltage to float high (above 4.6V), which the PCM interprets as an extremely high or invalid temperature signal.
The sensor's internal thermistor can fail open, producing a high-voltage signal that the PCM reads as a circuit-high condition.
A corroded, loose, or unplugged connector at the CHT sensor creates an open circuit condition that mimics a high-voltage reading.
The PCM's analog-to-digital converter for the CHT circuit may have an internal fault causing it to consistently read high voltage.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Inspect and repair wiring between the CHT sensor and PCM for open circuits
- Clean or replace the CHT sensor connector
- Replace the cylinder head temperature sensor
- Check for water intrusion or corrosion in the wiring harness