AutoCodes – Generic – P0400

P0400 Code - Exhaust Gas Recirculation Flow Malfunction

Quick Answer

Early Exhaust Gas Recirculation (EGR) systems component s include and EGR Valve, and Engine Control Îœodule (ECÎœ) Controlled Vacuum Switch Valve or EGR Solenoid and an EGR Vacuum Îœodulator. Common causes include Exhaust Gas Recirculation (EGR) volume control valve stuck closed, Faulty Exhaust Gas Recirculation (EGR) volume control solenoid valve, Faulty 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: P0400 indicates Exhaust Gas Recirculation Flow Malfunction.
Common causes: Common causes include Exhaust Gas Recirculation (EGR) volume control valve stuck closed, Faulty Exhaust Gas Recirculation (EGR) volume control solenoid valve, Faulty 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.

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Code Popularity 112,530

How popular is this code, among other codes? Medium

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
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0400 Description

Early Exhaust Gas Recirculation (EGR) systems component s include and EGR Valve, and Engine Control Îœodule (ECÎœ) Controlled Vacuum Switch Valve or EGR Solenoid and an EGR Vacuum Îœodulator. Depending on the engine and driving conditions, the ECÎœ will control the EGR Solenoid which will operate the EGR Vacuum Îœodulator to regulate the opening and closing of the EGR Valve.
The EGR system on recently built vehicles uses a step motor to control the flow rate of EGR from exhaust manifold. This motor has four winding phases. It operates according to the output pulse signal of the ECÎœ. Two windings are turned ON and OFF in sequence. Each time an ON pulse is issued, the valve opens or closes, changing the flow rate. When no change in the flow rate is needed, the ECÎœ does not issue the pulse signal. Î‘ certain voltage signal is issued so that the valve remains at that particular opening.

OBDII Code P0400 - Exhaust Gas Recirculation Flow Malfunction - AutoCodes.com — P0400 Code - Exhaust Gas Recirculation Flow Malfunction

What does this mean?

What are the Possible Causes of the DTC P0400?

Exhaust Gas Recirculation (EGR) volume control valve stuck closed
Faulty Exhaust Gas Recirculation (EGR) volume control solenoid valve
Faulty EGR Valve
Faulty EGR temperature sensor and circuit
Exhaust Gas Recirculation (EGR) solenoid valve harness is open or shorted
Exhaust Gas Recirculation (EGR) solenoid valve circuit poor electrical connection
Dead (Weak) battery

How to Fix the DTC P0400?

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

EGR flow malfunction could be caused by a clogged EGR valve or EGR tube. Before replacing any parts try cleaning the EGR valve, tube and passages.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0400 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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Information for Specific Makes

P0400 Acura — Exhaust Gas Recirculation System Leak Detected
P0400 Audi — Exhaust Gas Recirculation Flow
P0400 Buick — Exhaust Gas Recirculation Flow Malfunction
P0400 Cadillac — Exhaust Gas Recirculation Flow Malfunction
P0400 Chevrolet — Exhaust Gas Recirculation Flow Malfunction
P0400 Chrysler — Exhaust Gas Recirculation System Performance
P0400 Dodge — Exhaust Gas Recirculation System Performance
P0400 Ford — Exhaust Gas Recirculation Flow
P0400 GMC — Exhaust Gas Recirculation Flow Malfunction
P0400 Honda — Exhaust Gas Recirculation System Leak Detected
P0400 Infiniti — Exhaust Gas Recirculation Function- No/Low Flow Detected
P0400 Jeep — Exhaust Gas Recirculation System Performance
P0400 Lincoln — Exhaust Gas Recirculation Flow
P0400 Mazda — Exhaust Gas Recirculation Flow Malfunction
P0400 Mercedes-Benz — Exhaust Gas Recirculation Flow Malfunction
P0400 Mercury — Exhaust Gas Recirculation Flow
P0400 Mitsubishi — Exhaust Gas Recirculation Flow Malfunction
P0400 Nissan — Exhaust Gas Recirculation Function- No/Low Flow Detected
P0400 Saturn — Exhaust Gas Recirculation Flow Malfunction
P0400 Subaru — Exhaust Gas Recirculation Flow
P0400 Volkswagen — Exhaust Gas Recirculation Flow

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.

Frequently Asked Questions about P0400 Code

1. What are the common symptoms of OBDII code P0400 (Exhaust Gas Recirculation Flow Malfunction)?

- Common symptoms include rough idling, engine hesitation, decrease in fuel efficiency, and the illumination of the check engine light.

2. What are the possible causes of OBDII code P0400?

- The code P0400 can be triggered by issues such as a faulty EGR valve, clogged EGR passage, damaged vacuum hoses, or a malfunctioning EGR temperature sensor.

3. How can I diagnose the cause of OBDII code P0400?

- Diagnosing the issue involves checking the EGR valve for proper operation, inspecting the EGR passages for blockages, testing the vacuum lines for leaks, and verifying the EGR temperature sensor's functionality.

4. Can driving with OBDII code P0400 cause further damage to my vehicle?

- Continuing to drive with code P0400 may result in reduced engine performance, increased emissions, and potential damage to the catalytic converter over time.

5. How can I repair OBDII code P0400?

- Repairing code P0400 typically involves cleaning or replacing the EGR valve, clearing any blockages in the EGR passages, fixing or replacing damaged vacuum hoses, and addressing any issues with the EGR temperature sensor.

6. Is it safe to ignore OBDII code P0400?

- Ignoring code P0400 can lead to poor engine performance and increased emissions, so it is recommended to diagnose and repair the issue promptly.

7. Can a clogged catalytic converter trigger OBDII code P0400?

- Yes, a clogged catalytic converter can restrict exhaust flow, affecting EGR system operation and potentially triggering code P0400.

8. How long does it typically take to repair OBDII code P0400?

- The repair time for code P0400 can vary depending on the specific cause of the issue, but in many cases, it can be resolved within a few hours to a day.

9. Will resetting the check engine light resolve OBDII code P0400?

- Resetting the check engine light without addressing the underlying issue will not fix code P0400. It is important to diagnose and repair the root cause of the problem.

10. Can a dirty air filter cause OBDII code P0400 to appear?

- While a dirty air filter can affect engine performance, it is not a common direct cause of code P0400. It is recommended to focus on checking the EGR system components for this particular code.