P0400

Q: What does OBD2 code P0400 mean?

P0400 means: Exhaust Gas Recirculation Flow Malfunction. General EGR flow fault. The EGR system recirculates exhaust gases to reduce NOx emissions.

Exhaust Gas Recirculation Flow Malfunction

General EGR flow fault. The EGR system recirculates exhaust gases to reduce NOx emissions.

SeverityModerate

CategoryEmissions

Est. Repair Cost$50–$400

Code TypePowertrain

DIY RepairYes

⚡ Common Causes

›Clogged EGR valve with carbon
›Faulty EGR valve
›Blocked EGR passages
›EGR temperature sensor fault

⚠️ Symptoms

›Rough idle
›Check engine light
›Pinging or detonation under load
›Failed emissions test

✅ How to Fix — Step by Step

Step 1:Clean EGR valve with throttle body cleaner
Step 2:Test EGR valve operation
Step 3:Clean EGR passages
Step 4:Replace EGR valve if stuck

🔧 Diagnostic Tools Required

✔OBD-II Diagnostic Scanner
✔Digital Multimeter
✔Basic Hand Tools
✔Flashlight
✔Vehicle Service Manual

Using the correct diagnostic tools helps identify the root cause of P0400 before replacing parts unnecessarily. Always confirm the fault using live data and manufacturer-recommended diagnostic procedures.

💡 Pro Tip: Carbon-clogged EGR valves respond well to cleaning — disassemble and clean before replacing.

Repair Cost Estimate

Full Repair Estimate

$50–$400

DIY Possible?

YES

Severity

Moderate

Frequently Asked Questions

What does OBD2 code P0400 mean?+

P0400 stands for Exhaust Gas Recirculation Flow Malfunction. General EGR flow fault. The EGR system recirculates exhaust gases to reduce NOx emissions.

What causes code P0400?+

Clogged EGR valve with carbon; Faulty EGR valve; Blocked EGR passages; EGR temperature sensor fault

How do I fix code P0400?+

Clean EGR valve with throttle body cleaner; Test EGR valve operation; Clean EGR passages; Replace EGR valve if stuck

How much does it cost to fix P0400?+

Estimated repair cost for P0400 is $50–$400.

Is P0400 DIY-friendly?+

Yes — P0400 is generally DIY-friendly with basic tools.