Questions and Answers

Lincoln Towncar DTC P0401 Q. Hi there. I own a 1995 Lincoln Towncar. It has a V8 engine with 143,819 miles. The car drives wonderful and has had minor problems with it since I bought it. A few days ago I noticed the "check engine" light appear. I had it checked out on a diagnostic tester which gave it a P0401 code.

The performance of the car has not declined, it drives great with no noticeable signs of trouble. I have talked to a few people concerning the P0401 code and I have heard that it could be quite a number of things from the EGR valve to the oxygen sensor to a bad gas cap.

One thing I do want to mention is that once the guy hooked the PCM to the car and received the code, the "check engine" light went off for about 40-55 miles and it came back on again. It always remains on, without blinking.

Before sending it into the shop, I was wondering what you might suggest I do. Am I hurting the car by driving it?

Thanks,
Stephan

A. P0401 "Exhaust Gas Recirculation Flow Insufficient Detected" that there is not enough exhaust gas being admitted to the engine.

There are a number of things you can check, and others you need a scan tool to check.

What you can do is check for vacuum to the EGR valve. You can remove the EGR valve and see if it is stuck closed. Test it with a hand vacuum pump and see if it opens smoothly. Check the EGR valve orifice and make sure it is free and clear. Check and clean the EGR passages in the going to and from the EGR valve.

If this checks out, then the Differential Pressure Feedback EGR system will need to be scanned to check the EGR sensors and switches.