AutoCodes – Mercury – P1477 Mercury

P1477 Mercury Code - Medium Cooling Fan Control Primary Circuit Failure

Quick Answer

Monitors the medium fan control (MFC) primary circuit output from the Powertrain Control Module (PCM). Common causes include Faulty Cooling Fan Relay, Cooling Fan Relay harness is open or shorted, Cooling Fan Relay circuit poor electrical connection. 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: P1477 Mercury indicates Medium Cooling Fan Control Primary Circuit Failure.
Common causes: Common causes include Faulty Cooling Fan Relay, Cooling Fan Relay harness is open or shorted, Cooling Fan Relay circuit poor electrical connection.
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 1,460

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 Aug 24, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P1477 Mercury Description

Monitors the medium fan control (MFC) primary circuit output from the Powertrain Control Module (PCM). The test fails if: With the MFC output commanded on (grounded), excessive current draw is detected on the MFC circuit; or with the MFC circuit commanded off, voltage is not detected on the MFC circuit (the PCM expects to detect IGN START/RUN voltage coming through the medium speed FC relay coil to the MFC circuit).

OBDII Code P1477 Mercury - Medium Cooling Fan Control Primary Circuit Failure - AutoCodes.com — P1477 Mercury Code - Medium Cooling Fan Control Primary Circuit Failure

What does this mean?

What are the Possible Causes of the DTC P1477 Mercury?

Faulty Cooling Fan Relay
Cooling Fan Relay harness is open or shorted
Cooling Fan Relay circuit poor electrical connection
Faulty Powertrain Control Module (PCM)

How to Fix the DTC P1477 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 P1477 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.