AutoCodes – Mercury – P2251 Mercury

P2251 Mercury Code - O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1

Quick Answer

The Front Oxygen Sensor (O2 Sensor 1) is placed into the exhaust manifold. Common causes include Faulty Front Oxygen Sensor Bank 1, Front Oxygen Sensor Bank 1 harness is open or shorted, Front Oxygen Sensor Bank 1 circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means: P2251 Mercury indicates O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1.
Common causes: Common causes include Faulty Front Oxygen Sensor Bank 1, Front Oxygen Sensor Bank 1 harness is open or shorted, Front Oxygen Sensor Bank 1 circuit poor electrical connection.
Severity: Moderate - service should be scheduled soon.
Can I drive?: The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

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Code Popularity 1,546

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P2251 Mercury Description

The Front Oxygen Sensor (O2 Sensor 1) is placed into the exhaust manifold. It detects the amount of oxygen in the exhaust gas compared to the outside air. The heated oxygen sensor 1 has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The heated oxygen sensor 1 signal is sent to the Engine Control Module (ECM). The ECM adjusts the injection pulse duration to achieve the ideal air-fuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.

OBDII Code P2251 Mercury - O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1 - AutoCodes.com — P2251 Mercury Code - O2 Sensor Negative Current Control Circuit Open Bank 1 Sensor 1

What does this mean?

What are the Possible Causes of the DTC P2251 Mercury?

Faulty Front Oxygen Sensor Bank 1
Front Oxygen Sensor Bank 1 harness is open or shorted
Front Oxygen Sensor Bank 1 circuit poor electrical connection

How to Fix the DTC P2251 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 P2251 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.