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AutoCodes – Mercury – P1289 Mercury

P1289 Mercury Code - Cylinder Head Temperature Sensor Signal Greater Than Self-Test Range

Quick Answer

The Cylinder Head Temperature (CHT) Sensor is mounted into the wall of the cylinder head and is not connected to any coolant passages. Common causes include Wrong thermostat, Engine overheated, Low engine coolant level. 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
P1289 Mercury indicates Cylinder Head Temperature Sensor Signal Greater Than Self-Test Range.
Common causes
Common causes include Wrong thermostat, Engine overheated, Low engine coolant level.
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 6,827
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Aug 07, 2019
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Code P1289 Mercury Description

The Cylinder Head Temperature (CHT) Sensor is mounted into the wall of the cylinder head and is not connected to any coolant passages. The CHT sends a signal to the Powertrain Control Module (PCM) indicating the cylinder head temperature. If the temperature exceeds 126°C (-258°F), the PCM disables four fuel injectors at a time. The PCM will alternate which four injectors are disabled every 32 engine cycles. The four cylinders that are not being fuel injected act as air pumps to aid in cooling the engine. If the temperature exceeds 154 °C (310°F), the PCM disables all of the fuel injectors until the engine temperature drops below 154°C (310°F).
OBDII Code P1289 Mercury - Cylinder Head Temperature Sensor Signal Greater Than Self-Test Range - AutoCodes.com
P1289 Mercury Code - Cylinder Head Temperature Sensor Signal Greater Than Self-Test Range
What does this mean?

What are the Possible Causes of the DTC P1289 Mercury?

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

How to Fix the DTC P1289 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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1289 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.

Need more information about the P1289 Mercury code?

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Need Help with the Code?

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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.

Frequently Asked Questions about P1289 Mercury Code

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