P0400
PPowertrainEGR Flow Malfunction
What does this code mean?
Severity : MediumP0400 indicates a general fault in exhaust gas recirculation (EGR) flow. The ECU compares the recirculated gas flow it expects with what its sensors measure and finds a mismatch. The cause can be the EGR valve itself, clogged passages or the electrical control circuit.
Symptoms
- Check engine light on.
- Rough or unstable idle.
- Hesitation or loss of power under acceleration.
- Black smoke from the exhaust on diesel engines.
- Higher fuel consumption.
Possible causes
- EGR valve clogged with carbon or stuck.
- Blocked EGR passages or EGR cooler.
- Damaged EGR valve connector or wiring.
- Faulty EGR valve position sensor.
- Leaking vacuum hose or faulty solenoid on vacuum-operated systems.
- Mass airflow or intake pressure sensor giving incorrect readings.
Diagnosis and repair
- Read all stored codes and the freeze frame data recorded with the fault.
- Inspect the EGR valve connector, wiring and any vacuum hoses.
- Compare commanded and actual EGR valve position in live data.
- Clean the EGR valve and passages, or replace the valve if it stays stuck.
- Clear the code and road test to confirm the repair.
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Code
P0400
Category
Powertrain
Prefix
P
Standard
OBD-II / SAE J2012