What is diagnostic code 401 on mark 8?

DTC P0401 - Insufficient EGR Flow Detected

The P0401 code is set when the PCM detects insufficient Exhaust Gas Recirculation (EGR) flow. The PCM monitors the EGR system to ensure that it is functioning properly. If the PCM detects that the EGR system is not working properly, it will set the P0401 code.

Possible Causes

* Faulty EGR valve

* Stuck or clogged EGR valve

* Vacuum leak in the EGR system

* Faulty EGR position sensor

* Faulty PCM

Diagnostic Tips

* Inspect the EGR valve and EGR system for any damage or leaks.

* Check the vacuum lines to the EGR valve for any leaks.

* Test the EGR position sensor to make sure it is working properly.

* If all of the above checks out okay, then the PCM may need to be replaced.

Symptoms of DTC P0401

* Check Engine Light on

* Rough idle

* Loss of power

* Poor fuel economy

* Emissions failure

Repair Tips

* If the EGR valve is faulty, it will need to be replaced.

* If the EGR system is clogged, it will need to be cleaned.

* If there is a vacuum leak in the EGR system, it will need to be repaired.

* If the EGR position sensor is faulty, it will need to be replaced.

* If the PCM is faulty, it will need to be reprogrammed or replaced.