Ford P1289 Code: Cylinder Head Temperature Sensor Circuit High
The CHT sensor signal on your Ford is stuck near 5 volts, which the PCM reads as an impossibly cold engine.
At a glance
Severity: Moderate
- Meaning
- Cylinder Head Temperature Sensor Circuit High
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$600
- DIY difficulty
- Easy
The cylinder head temperature (CHT) sensor is a thermistor that the PCM feeds with a 5 V reference: the hotter the head, the lower the sensor's resistance and the lower the signal voltage. P1289 means the voltage has risen to the top of the range, which is what happens when the circuit is open, such as a disconnected plug, a broken wire, a corroded pin or a sensor that has failed open. The PCM then sees a temperature far below freezing, well colder than any real engine. On many Fords the CHT is the main or only engine temperature input, so the PCM falls back to an estimated value, typically runs the cooling fans continuously, and the temperature gauge may drop to cold or zero. Most importantly, the overheat protection behind P1285 and P1299 can no longer rely on a real measurement, so the engine is effectively running without its temperature watchdog.
Can I keep driving? Short trips are usually possible, but the engine has lost its real temperature reading and overheat protection. Keep an eye on the coolant level, avoid towing and long highway runs in hot weather, and get the circuit fixed promptly.
How to read P1289
- P Powertrain
- 1 Manufacturer-specific
- 2 Fuel & air (injector circuit)
- 89 Specific fault
Symptoms
- Check engine light with P1289
- Temperature gauge reads cold, drops to zero or doesn't move at all
- Cooling fans running constantly, even with a cold engine
- Hard starting when hot and a rich smell, because the PCM thinks the engine is cold
- Higher fuel consumption
- Heater and A/C behaving oddly on models that use the CHT value for climate control
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Connector unplugged, not fully latched or corroded, often after work near the intake manifold
- CHT sensor failed open internally
- Signal or signal-return wire broken or chafed in the harness
- Previously removed sensor reused and no longer making proper contact
- PCM input fault (rare)
Diagnosis step by step
Read CHT on a cold engine
After the vehicle has sat for several hours, turn the key on and read CHT in live data. It should match the outside air temperature within a few degrees; a reading around -40 °F confirms an open circuit rather than an intermittent fault.
Tools: OBD-II scanner
Find and inspect the connector
Locate the CHT sensor, which is threaded into the cylinder head, often near the thermostat housing or under the intake manifold on V engines. Check that the plug is fully latched and look for green corrosion or pushed-back pins.
Tools: Flashlight
Do a jumper test
Unplug the sensor and, with the key on, briefly bridge the two harness terminals with a fused jumper while watching live data. If the reading jumps to maximum hot, the wiring and PCM are fine and the sensor is open; if nothing changes, the fault is in the harness.
Tools: OBD-II scanner, Multimeter
Measure the sensor
Check the sensor resistance across its terminals. A thermistor shows tens of kilohms when cold and drops steadily as it warms; an infinite reading means it has failed open.
Tools: Multimeter
Check the harness
Measure continuity of both wires between the sensor plug and the PCM connector, and flex the harness while measuring. Pay special attention to spots where it passes hot metal or sharp brackets.
Tools: Multimeter
Install a new sensor correctly
Ford specifies CHT sensors as one-time-use parts, so never reinstall one that has been removed. Tighten to the specified torque; on the few designs that sit in coolant, top up and bleed the system afterward.
Tools: Torque wrench
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reconnect or clean CHT connector | Yes | $0–$80 |
| Replace CHT sensor | Yes | $80–$260 |
| Repair CHT wiring | No | $100–$300 |
| Replace sensor where access requires removing the intake manifold | No | $250–$600 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P1289 turns on the check engine light and fails an OBD emissions test. After the repair, drive until the readiness monitors have run, since several of them depend on a valid engine temperature.
Frequently asked questions
Why does 'circuit high' mean the engine reads cold?
The CHT sensor's resistance drops as it heats up, which pulls the signal voltage down. An open circuit leaves the voltage at the top of the range, and the PCM translates that into an extremely cold temperature.
Can I reuse the old CHT sensor if I just remove it to clean it?
No. Ford treats the CHT sensor as a one-time-use part because its seating and contact are set on first installation. A reinstalled sensor may not read correctly.
Why are my cooling fans running all the time?
When the PCM loses the CHT signal it can't tell how hot the engine is, so it turns the fans on as a precaution. The fans should return to normal once the sensor circuit is fixed.
Is it safe to drive with P1289?
For short distances, usually. The real risk is that an actual overheat would go unnoticed, because the protection strategy has no valid reading. Watch the coolant level and don't delay the repair.
Sources
- Manufacturer public service information (cross-checked)
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