P1285 Code: Cylinder Head Temperature Sensor Circuit Excessive Time to Closed Loop
🟠 Moderate severity · drivable
The engine will usually run, but it may run rich, idle rough, or overheat, so get it checked soon.
What P1285 means
The engine computer uses the cylinder head temperature (CHT) sensor to know how warm the engine is. P1285 means the engine took too long to reach closed loop, the mode where the computer fine-tunes the fuel mix using the oxygen sensors. That delay usually points to a faulty CHT sensor or its wiring. This code is most often reported on Chrysler, Dodge, and Jeep vehicles.
Symptoms
- Check engine light is on
- Poor fuel economy
- Rough idle or hesitation
- Possible hard starting
Common causes
- most common: Faulty cylinder head temperature (CHT) sensor
- common: Wiring or connector problem in the CHT sensor circuit
- common: Engine running cooler than normal, such as a stuck-open thermostat
- rare: Engine computer (PCM) fault
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Test the CHT sensor with a multimeter and replace it if it reads out of spec | Yes | $30–120 |
| Inspect and repair the CHT sensor wiring and connector | Yes | $20–100 |
| Replace a stuck-open thermostat that keeps the engine from warming up | Yes | $40–150 |
Frequently asked questions
Can I drive with a P1285 code?
Usually yes for a short time, but watch the temperature gauge. If the engine overheats, idles rough, or stalls, stop driving and get it checked.
What does 'excessive time to closed loop' mean?
Closed loop is the mode where the computer fine-tunes the fuel mix based on oxygen sensor readings. P1285 means the engine took too long to reach that mode, which usually points to a problem with the cylinder head temperature sensor circuit.
Is P1285 specific to certain vehicles?
It's most often seen on Chrysler, Dodge, and Jeep vehicles. On some other makes the same number can mean something different, so check your vehicle's service information.
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Updated 2026-08. This page is informational and not a substitute for professional diagnosis.