AutoCodes – Mercury – P1408 Mercury

P1408 Mercury Code - EGR Flow Out Of Self-Test Range

Quick Answer

The Exhaust Gas Recirculation (EGR) system recirculates a portion of the exhaust gasses into the intake manifold under average vehicle driving conditions to reduce combustion temperatures and exhaust gas NOx content. Common causes include Faulty Exhaust Gas Recirculation (EGR) Valve, Exhaust Gas Recirculation (EGR) Valve Vacuum hose off or defective, Plugged Exhaust Gas Recirculation (EGR) Valve. 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: P1408 Mercury indicates EGR Flow Out Of Self-Test Range.
Common causes: Common causes include Faulty Exhaust Gas Recirculation (EGR) Valve, Exhaust Gas Recirculation (EGR) Valve Vacuum hose off or defective, Plugged Exhaust Gas Recirculation (EGR) Valve.
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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 2,551

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 Aug 20, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code P1408 Mercury Description

The Exhaust Gas Recirculation (EGR) system recirculates a portion of the exhaust gasses into the intake manifold under average vehicle driving conditions to reduce combustion temperatures and exhaust gas NOx content. The amount of exhaust gas recirculated varies from zero with a cold engine to a fixed rate for a hot engine with intermediate load and low engine speed.
This test is performed during the Key On Engine Running (KOER) on demand self-test only. The EGR system is commanded ON at a fixed engine speed. The test fails and the Diagnostic Trouble Code (DTC) is output when the measured EGR flow falls above or below the required calibration.

OBDII Code P1408 Mercury - EGR Flow Out Of Self-Test Range - AutoCodes.com — P1408 Mercury Code - EGR Flow Out Of Self-Test Range

What does this mean?

What are the Possible Causes of the DTC P1408 Mercury?

Faulty Exhaust Gas Recirculation (EGR) Valve
Exhaust Gas Recirculation (EGR) Valve Vacuum hose off or defective
Plugged Exhaust Gas Recirculation (EGR) Valve

How to Fix the DTC P1408 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 P1408 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 P1408 Mercury code?

Need more information on how to fix the P1408 Mercury code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P1408 Mercury code diagnosed by a professional: Find a repair shop in your area

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.