AutoCodes – Ford – P0491 Ford

P0491 Ford Code - Secondary Air Injection System Insufficient Flow Bank 1

Quick Answer

An air pump is used on the vehicle to lower tail pipe emissions on start-up. Common causes include Secondary air pump with no or low air flow, Secondary air bypass solenoid leaking /blocked or stuck open /closed, Secondary AIR air hose restricted. Severity is Low - monitor the vehicle and repair when practical. The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

What it means: P0491 Ford indicates Secondary Air Injection System Insufficient Flow Bank 1.
Common causes: Common causes include Secondary air pump with no or low air flow, Secondary air bypass solenoid leaking /blocked or stuck open /closed, Secondary AIR air hose restricted.
Severity: Low - monitor the vehicle and repair when practical.
Can I drive?: The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

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Code Popularity 20,958

How popular is this code, among other codes? Low

Repair Importance Level

Low (Monitor) (1 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 13, 2020

Description
Possible Causes
How To Fix
Tech Notes ▶
Cost to Diagnose
Comments
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Code P0491 Ford Description

An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM) grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.

OBDII Code P0491 Ford - Secondary Air Injection System Insufficient Flow Bank 1 - AutoCodes.com — P0491 Ford Code - Secondary Air Injection System Insufficient Flow Bank 1

What does this mean?

What are the Possible Causes of the DTC P0491 Ford?

Secondary air pump with no or low air flow
Secondary air bypass solenoid leaking /blocked or stuck open /closed
Secondary AIR air hose restricted
Secondary air vacuum hoses restricted or leaking

How to Fix the DTC P0491 Ford?

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

User Submitted Video

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0491 Ford 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.