P0401

Note: The manufacturer did not provide further diagnostic information for DTC P0401 in this model year beyond the information as follows from Honda's "Advanced Diagnostics".


DTC P0401: Exhaust Gas Recirculation (EGR) Insufficient Flow





General Description
The exhaust gas recirculation (EGR) system reduces oxides of nitrogen (NOx). NOx is generated by high combustion temperatures. The EGR system lowers peak combustion temperature by recirculating exhaust gas into the air/fuel mixture, thus reducing NOx. The manifold absolute pressure (MAP) sensor detects intake manifold pressure (vacuum) changes and the engine control module (ECM)/powertrain control module (PCM) determines if the amount of exhaust gas recirculation is sufficient. When starting to decelerate with the throttle valve closed, the EGR valve is closed. If the intake manifold pressure changes only slightly while the EGR valve opens fully and closes again within a specified time period, a malfunction is detected and a DTC is stored.





Monitor Execution, Sequence, Duration, DTC Type





Enable Conditions





Malfunction Threshold
The difference between the MAP value before and after the Enable Conditions are met is no more than the values in the
table. The change in pressure should occur for at least 3.5 seconds.





Driving Pattern

1. Start the engine. Hold the engine speed at 3,000 rpm without load (in Park or neutral) until the radiator fan comes on.
2. Drive the vehicle at a speed between 25 - 55 mph (40 - 88 km/h) for at least 5 minutes.
3. Then, drive at a steady speed between 55 - 75 mph (88 - 120 km/h) for at least 5 seconds.
4. Decelerate with the throttle valve fully closed for at least 3.5 seconds.

- If you have difficulty duplicating the DTC, retest after turning off electrical components such as the audio system and A/C, and try a different gear position.

- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details

Conditions for illuminating the MIL
When a malfunction is detected during the first drive cycle, a Temporary DTC is stored in the ECM/PCM memory. If the malfunction recurs during the next (second) drive cycle, the MIL comes on and the DTC and the freeze frame data are stored.

Conditions for clearing the MIL
The MIL will be cleared if the malfunction does not recur during three consecutive trips in which the diagnostic runs. The MIL, the DTC, the Temporary DTC, and the freeze frame data can be cleared by using the scan tool Clear command or by disconnecting the battery.