P0401 AGAIN! Help

[94GrandPrixSE]

02 Grand Prix GTP 80k

P0401 - Insufficient EGR flow.

I thought i finaly rid myself of this code, nope sure enough 300 miles after I swapped EGR valves from the one in my 03 GT and replaced the PCV valve and gasket. It takes about 2 weeks for this code to come back, I have went over every single vacuum line several times the tube that goes from the EGR valve to the engine is fine, there is no carbon build up. I really like to keep out of the shops and in my garage when something goes wrong but I just cant get this one. I have read that a bad MAP sensor can cause this same code but would like to confirm that is possible. Thanks in advance to anyone with any advice.

[BillBoost37]

Ok, I'll confirm that I said that. No problem.

Meanwhile, if you want to understand it for yourself, instead of taking my word on it and having me merely confirm it for you. Google "GM DTC P0401". Read various things. What you'll learn is why a map sensor might cause a flow code and why it's not necessarily a vacuum or EGR issue.

Sometimes codes are named poorly. In my eyes, this is one of them. it has EGR in the title and maybe GM found it to commonly be an EGR. I've seen it typically be anything but the EGR. Hence.. what monitors the flow in the intake manifold? Right.

[94GrandPrixSE]

Thanks for the reply, ill replace that sensor after work, why does the code only come up after long amounts of time? my 94 I had always gave me problems with the egr code as soon as i cleared it would be on in a matter of a few miles.

[BillBoost37]

The code comes up after long amounts of time, because you didn't read up on it. Sorry..had to toss a little humor in.

It's based on how the test runs, when it runs etc.

[94GrandPrixSE]

The code comes up after long amounts of time, because you didn't read up on it. Sorry..had to toss a little humor in.

It's based on how the test runs, when it runs etc.

Well I replaced the MAP sensor wont know if it fixed it for a while, ill re post if i have anymore problems thanks again guys!

[94GrandPrixSE]

2 weeks later light is back on anyone know what my next step should be?

[tomc]

I am having the same issue. 2000 GTP 93K Miles. Things that have been replaced so far are the Aft O2 sensor, MAP sensor, PCV valve, removed and cleaned throttle body and all lines and replaced EGR. The EGR was a cheap one from E-Bay which may still be the problem. It is going in for a scan on Saturday.

I have read that if all else fails, the PCM may have to be flashed because the parameters will change over 16 years. Anyone have any insight on this?