P0400 Fault Code

Exhaust Gas Recirculation Flow Malfunction

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0400 fault code indicates a problem with the exhaust gas recirculation (EGR) system, which is responsible for reducing nitrogen oxide (NOx) emissions by recirculating a portion of the exhaust back into the engine's intake. When there is a flow malfunction in the EGR system, the engine control module (ECM) detects an issue with the amount of exhaust gas recirculated and triggers this code.

What are the symptoms of the P0400 code?

Common symptoms associated with a P0400 fault code include:

• Illuminated check engine light
• Rough idle or stalling, especially at low speeds
• Decreased engine performance and acceleration
• Increased emissions and potential failure of emissions tests
• Engine knocking or pinging noise due to improper combustion.

What causes the P0400 code?

Several factors can lead to a P0400 fault code, including:

• A clogged or faulty EGR valve
• Blockages in the EGR passages
• A bad EGR temperature sensor
• Issues with wiring or connections related to the EGR system
• A malfunctioning engine control module (ECM) that fails to control the EGR system properly.

How to fix P0400?

To resolve a P0400 fault code, the following steps may be taken:

• Inspect and clean the EGR valve and passages to remove any carbon buildup or blockages.
• Replace the EGR valve if it is found to be faulty or unresponsive.
• Check and repair any damaged wiring or connectors in the EGR system.
• Test and replace the EGR temperature sensor if it is not functioning correctly.
• Depending on the diagnosis, reprogram or replace the ECM if it is determined to be malfunctioning.