P0401 – Meaning, Causes, Symptoms, & Fixes
Code P0401 Definition
Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
Code P0401 Meaning
The exhaust gas recirculation (EGR) recirculates small amounts of exhaust back into the combustion chambers of the engine in order to decrease the combustion temperature, thereby reducing the formation of smog-producing nitrogen oxides. EGR valves can malfunction by becoming stuck open or closed due to carbon buildup. When the trouble code P0401 is set, CO2 is reintroduced to the combustion chamber at the incorrect time or in incorrect amounts, which does not decrease the combustion temperature sufficiently enough to prevent the increase of NOx. This is likely due to faulty or clogged EGR valve or carbon buildup in the intake manifold or on the EGR temperature sensor.
Symptoms of Code P0401
- Check Engine Light
- Failed emissions test
- Slower acceleration
- Ignition pinging
Causes of Code P0401
- Clogged or restricted EGR passages due to excess carbon
- Faulty EGR valve
- EGR temperature sensor is covered with carbon
Code P0401 Severity – Moderate
Code P0401 can cause can cause excessive internal engine ignition and pre-ignition damage to the pistons and valves.
Code P0401 Common Diagnosis Mistakes
Replacing the EGR valve without checking the air passages of the intake manifold or the temperature sensor
Code P0401 Diagnosis Steps
How To Diagnose P0401
- Visually inspect the vacuum hoses, wiring, and any other connections to the EGR valve that may interrupt air flow to the intake manifold. If you find damages or cracks in any of these connections, replace and clear your check engine light
- Use your car’s service manual to locate and check the vehicle’s EGR temperature sensor for any carbon buildup that may interfere with its readings
- Remove carbon using speedometer cable and throttle body cleaner
- Use your car’s service manual to locate and check the EGR valve for any carbon buildup. Check out this video for a visual reference. If you find carbon buildup, use a speedometer cable and throttle body cleaner to remove carbon blocking any air passages.
- Use your car’s service manual to locate and remove the intake manifold to check for carbon build up. Check out this video for a visual reference
- Remove all hoses connected to the intake
- Remove air intake hose that is connected to the throttle body
- Remove throttle body
- Remove intake manifold to inspect for carbon buildup – use speedometer cable and throttle body cleaner to remove carbon buildup
- Place intake manifold back in and reconnect hoses, throttle body, etc.
- If these steps do not clear your Check Engine Light, you may need to visit a mechanic because there may be internal electrical issues.