P0401 — Exhaust Gas Recirculation (EGR) Flow Insufficient
Moderate severityWhat it means
Less exhaust gas is being recirculated into the intake than the engine control unit expects. The EGR system lowers combustion temperatures to reduce NOx emissions; with insufficient flow, the engine may ping under load and emissions rise.
Common symptoms
- Check engine light
- Pinging or knocking under load
- Rough idle in some cases
- Failed emissions inspection
Likely causes
- Carbon-clogged EGR valve or passages (most common)
- Faulty EGR valve not opening
- Bad feedback sensor (DPFE/MAP) misreporting flow
- Blocked or cracked vacuum lines to the valve
What to check first
- Remove and inspect the EGR valve for carbon buildup; clean it and the passages
- Command the valve open with a scan tool and watch the engine response
- Check vacuum lines and electrical connector
- Verify the feedback sensor reading in live data
Can you keep driving?
Drivable, but pinging under load can damage the engine over time — avoid heavy loads until repaired.
Scan, log and diagnose with MechanicAI
Plug a Bluetooth OBD2 adapter into your car and let MechanicAI turn raw data into answers:
- Scan, read and clear fault codes in seconds
- Inspect every sensor with live data
- Create instant logs and automatic trip records
- And above all — analyze it all with AI for the most likely cause and clear next steps.
Related codes
All information, explanations and guidance on this page are general preliminary information only. They are estimates and may be entirely wrong, incomplete or inaccurate, or may not apply to your vehicle at all. Never take any action based on this content alone — do not decide to keep driving, clear codes, replace parts, repair or otherwise work on your vehicle based only on what you read here. In every case, and for any final decision, you must consult qualified technical personnel (a professional mechanic, an authorized service centre or an engineer) and obtain their approval before acting. MechanicAI accepts no liability or responsibility whatsoever for any damage, fault, injury, loss or outcome that may arise — directly or indirectly — from using or relying on this information, for any reason and under any circumstances. By using this page you acknowledge and accept these terms.