AutoCodes – Mercury – P1285 Mercury

P1285 Mercury Code - Cylinder Head Over Temperature Condition

Quick Answer

The Cylinder Head Temperature (CHT) Sensor is a thermistor device in which resistance changes with temperature. Common causes include Engine overheated, Low engine coolant level, Faulty Cylinder Head Temperature (CHT) Sensor. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P1285 Mercury indicates Cylinder Head Over Temperature Condition.
Common causes: Common causes include Engine overheated, Low engine coolant level, Faulty Cylinder Head Temperature (CHT) Sensor.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 4,983

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 11, 2020

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
Comments
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Code P1285 Mercury Description

The Cylinder Head Temperature (CHT) Sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the Powertrain Control Module (PCM) corresponding to temperature.
The CHT sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor can provide complete engine temperature information and can be used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system concern such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp-home capability.
The Diagnostic Trouble Code (DTC) indicates the Cylinder Head Over Temperature Sensed Indicates an engine overheat condition was sensed by the cylinder head temperature sensor.

OBDII Code P1285 Mercury - Cylinder Head Over Temperature Condition - AutoCodes.com — P1285 Mercury Code - Cylinder Head Over Temperature Condition

What does this mean?

What are the Possible Causes of the DTC P1285 Mercury?

Engine overheated
Low engine coolant level
Faulty Cylinder Head Temperature (CHT) Sensor
Cylinder Head Temperature Sensor harness is open or shorted
Cylinder Head Temperature Sensor circuit poor electrical connection

How to Fix the DTC P1285 Mercury?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

Indicates an engine overheat condition was sensed by the cylinder head temperature sensor.

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1285 Mercury code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.