DTC Advanced Diagnostics: P0401
DTC P0401:Exhaust Gas Recirculation (EGR) Insufficient Flow General Description
The exhaust gas recirculation (EGR) valve, which is controlled by the powertrain control module (PCM), is opened and the exhaust gas flows through the EGR valve, the intake manifold, and the EGR passage. The exhaust gas is circulated into the air/fuel mixture to lower combustion temperatures, thus reducing oxides of nitrogen (NOx) emissions. The EGR flow is inspected as follows. The EGR valve is closed during deceleration with the throttle valve fully closed. Then the PCM fully opens the EGR valve. After a set time, the PCM computes the ratio of the present EGR flow to the normal EGR flow by monitoring the fluctuation of the intake manifold pressure between when the EGR valve is fully opened and when it is fully closed. If the EGR flow rate is lower than normal, the PCM detects a malfunction and stores a DTC. Monitor Execution, Sequence, Duration, DTC Type
Enable Conditions
Malfunction Threshold (USA and Canada models)
The ratio of the current EGR flow to the normal EGR flow is 20 % or less for at least 3.5 seconds. The ratio is derived from the actual and estimated MAP values before and after the EGR valve was opened. The estimated MAP difference value is shown in the table.
Malfunction Threshold (Mexico models)
The ratio of the current EGR flow to the normal EGR flow is 20 % or less for at least 3.5 seconds. The ratio is derived from the actual and estimated MAP values before and after the EGR valve was opened. The estimated MAP difference value is shown in the table.
Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
Confirmation Procedure
Operating Condition
With the HDS
None. Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored. Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the 12 volt battery. |