Q: The check engine light came on my 1997 Geo Prizm, I ran the test and the code P0401 Egr flow insufficient.

The code means that there is too little flow of exhaust gases back into the intake manifold during times of commanded EGR. Trouble code P0401 will often set if the passageway from the EGR valve to the intake is blocked with carbon and it is that blockage that prevents the required flow of exhaust. To clean the passageway effectively, you might have to remove the throttle body. In extreme cases, that is if access is difficult or the carbon has become rock hard the intake has to be removed. However, if you use a powerful solvent and appropriate tools you can usually get it clear. If you car is equipped with an EGR temperature sensor, carbon build up on the sensor will also cause that code to set. I would definitely clean the EGR passageways first though. If you desire this service on a mobile basis, simply request a check engine light diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.