P0400

Exhaust Gas Recirculation (EGR) "A" Flow Malfunction

Car Fault Codes Emissions & exhaust

Can you still drive? Yes, normally

Who can fix it? Needs a workshop

Typical repair time 1 hour – 3 hours

Typical cost SAR 150 to 1,800

What it means

The engine computer has detected that exhaust gas recirculation (EGR) flow does not match what it expects when it commands the EGR valve. EGR returns a small amount of exhaust to the intake to lower combustion temperature and emissions, so a fault mainly affects emissions and can cause pinging or a rough idle.

Symptoms5

Check engine light on.
Light pinging or knocking when accelerating or climbing hills.
Occasional rough or unstable idle.
Failed emissions test.
Small change in fuel economy or performance.

Possible causes5

Carbon buildup in the EGR valve or its passages.
EGR valve stuck open or closed.
Faulty EGR position sensor, EGR pressure sensor or their hoses.
Weak vacuum supply or a faulty control solenoid on vacuum-operated systems.
Damaged wiring or connectors in the system.

How to diagnose5

Read all codes and the freeze frame data to see when the code was set.
Command the EGR valve open with a scan tool at idle; a working valve makes the engine run noticeably rough.
Inspect the valve and its passages for carbon buildup.
Check the vacuum hoses and control solenoid if the system has them.
Compare the EGR position or pressure sensor signal with the manufacturer specification and check its wiring.

How to fix5

Repair damaged vacuum hoses, wiring or connectors.
Clean carbon from the EGR valve and its passages.
Replace the EGR position or pressure sensor if it is proven faulty.
Replace the EGR valve if it stays stuck or does not respond to commands.
Clear the codes and drive until the EGR self-test completes.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low when carbon cleaning or a hose repair is enough, and rises when the EGR valve itself must be replaced, especially an electronic valve.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Is this code harmful to the engine?

Not immediately, but too little EGR flow can cause knocking under load, and too much can cause a rough idle or stalling, so repair it soon.

Is cleaning the EGR valve enough?

Often yes, since carbon is the most common cause. If the intake passages are blocked or the valve has an electrical fault, cleaning alone will not fix it.

This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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