AutoCodes – Mercury – P0203 Mercury

P0203 Mercury Code - Injector Circuit Malfunction Cylinder 3

Quick Answer

The Engine Control Module (ECM) supplies voltage to each fuel injector on the high control circuits. Common causes include Faulty Fuel Injector #3, Fuel Injector 3 harness is open or shorted, Fuel Injector #3 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: P0203 Mercury indicates Injector Circuit Malfunction Cylinder 3.
Common causes: Common causes include Faulty Fuel Injector #3, Fuel Injector 3 harness is open or shorted, Fuel Injector #3 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 504

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 Jun 01, 2022

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
Comments
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Code P0203 Mercury Description

The Engine Control Module (ECM) supplies voltage to each fuel injector on the high control circuits. The ECM energizes each fuel injector by grounding the low control circuit of the fuel injector. The ECM monitors the status of the fuel injector circuits. When a fuel injector circuit condition is detected by the ECM, the affected fuel injector(s) is disabled. The Diagnostic Trouble Code (DTC) will be set when the ECM detects the fuel injector control circuit is open for greater than 2 s.

OBDII Code P0203 Mercury - Injector Circuit Malfunction Cylinder 3 - AutoCodes.com — P0203 Mercury Code - Injector Circuit Malfunction Cylinder 3

What does this mean?

What are the Possible Causes of the DTC P0203 Mercury?

Faulty Fuel Injector #3
Fuel Injector 3 harness is open or shorted
Fuel Injector #3 circuit poor electrical connection

How to Fix the DTC P0203 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

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0203 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.