P0400 severity depends on the specific fault. While some causes are minor (e.g., sensor failure), others can affect performance or emissions. Diagnosis is recommended.

Can I drive with P0400?

Short trips may be possible, but prolonged driving with P0400 active is not advised until the root cause is identified and repaired.

Will P0400 clear itself?

P0400 may clear if the fault is intermittent, but it will likely return if the underlying issue is not resolved. Use a scanner to monitor pending and confirmed codes.

P0400 - Exhaust Gas Recirculation Flow Malfunction

P0400 is a Diagnostic Trouble Code (DTC) indicating a fault related to Exhaust Gas Recirculation Flow Malfunction. This code falls within the Powertrain (P) category and is standardized across OBD2-equipped vehicles. When P0400 is stored in the engine control module (ECM), it means the onboard diagnostics have detected a malfunction or out-of-range condition in the Exhaust Gas Recirculation Flow Malfunction circuit or system.

P0400 - Exhaust Gas Recirculation Flow Malfunction

What is P0400?

P0400 is a Diagnostic Trouble Code (DTC) indicating a fault related to Exhaust Gas Recirculation Flow Malfunction. This code falls within the Powertrain (P) category and is standardized across OBD2-equipped vehicles.

When P0400 is stored in the engine control module (ECM), it means the onboard diagnostics have detected a malfunction or out-of-range condition in the Exhaust Gas Recirculation Flow Malfunction circuit or system.

Common Symptoms

Check Engine Light illuminated
Possible drivability issues
System performance concerns
Diagnostic required

Possible Causes

Faulty sensor, actuator, or wiring
Software or calibration issue
Mechanical failure in related system
Intermittent electrical fault

Step-by-Step Diagnosis

Connect an OBD2 scanner and confirm the code is present. Note any additional codes.
Review freeze frame data to understand engine conditions when the code was set.
Visually inspect the Exhaust Gas Recirculation Flow Malfunction and related wiring harness for damage, corrosion, or loose connections.
Perform a wiggle test on wiring while monitoring live data (if applicable).
Use a multimeter to check sensor/actuator resistance, voltage, and ground integrity.
Compare live data readings to factory specifications.
If circuit-related, trace the wiring diagram and test for opens, shorts, or high resistance.
Clear the code and perform a road test to verify repair.

Recommended Repairs

Replace or repair the faulty Exhaust Gas Recirculation Flow Malfunction if testing confirms failure.
Repair any damaged wiring, connectors, or terminals. Ensure proper routing and secure mounting.
Clean components (throttle body, MAF sensor, EGR valve) if contamination is present.
Update ECM/TCM software if a technical service bulletin (TSB) applies.
Replace related fluids (transmission fluid, coolant) if degraded or incorrect.
Verify repair by clearing codes and completing an extended road test under various conditions.

Related Diagnostic Trouble Codes

External References and Forum Discussions

Disclaimer

The information provided is for educational purposes only. Always consult a qualified mechanic for accurate diagnosis and repair. Diagnostic Trouble Codes can have multiple causes, and proper testing is essential before replacing parts.

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P0400 - Exhaust Gas Recirculation Flow Malfunction

P0400 Diagnostic Trouble Code