P0400 · Exhaust Gas Recirculation Flow Malfunction

Key facts

Definition and circuit logic

• Exhaust Gas Recirculation Flow Malfunction

First-fault record

• Preserve rpm, load, speed, temperature, system voltage and relevant commanded/actual values from the first event.

Diagnostics and measurement

Symptoms

• Evaluate the symptom and companion codes from the same event as P0400.

Freeze frame and initial capture

• Preserve rpm, load, speed, temperature, system voltage and relevant commanded/actual values from the first event.

Common diagnostic mistakes

• Do not treat the code label as a definitive failed-part diagnosis; compare command, feedback and physical measurement.

Post-repair verification

• After repair, safely reproduce the original fault condition and recheck DTC status.

Safety

• Use manufacturer service information for application-specific procedures and exact thresholds.

Possible causes

• Within EGR / air / emissions, evaluate power/ground, sensor/actuator, wiring, controller and mechanical/hydraulic causes together.

Live data to monitor

• Record commanded and actual values with system voltage and companion DTCs.

Measurement sequence for a DTC

1. Record which module stored the code and under what conditions.
2. Review freeze-frame and simultaneous codes together.
3. Verify power, ground and voltage-drop basics.
4. Compare commanded and actual values in live data.
5. Recreate the operating condition after repair.