Thanks I appreciate all the input from everyone. Worked in a computer facility and know sometimes it's the simplest thing to turn off the idiot lights. My husband was called back from vacation because a machine was desperately needed and not working. The company had called the pro's but they couldn't come for several days. When he got there, the plug was not in the wall socket!!! Life always interesting.
Looked up a 3.4L and code is excessive EGR flow detected; If your truck is still idling ok the valve is not stuck open. The EGR valve is used to enrich the fuel mixture while driving. The computer has recognized the enrichment is more than it has asked for. The engine is running more rich than it should. This condition is better than lean, where your not getting enough gas. 1 Simple check is to see if you can see daylight while looking into the air filter, (you have to remove the filter from the housing first, of course, and hold it up to the light) before somebody corrects me. If dirty change the filter. and take it somewhere to have it tested. Hope this helps answer your question. If not post and let me know.
Thanks! My husband replaced the air filter, how do leaves get into a sealed box with a filter, it was filthy. The check engine light has not gone out but I also haven't driven it very far which it sounds to me like the electronics do their checking with sustained speed. Will take it out tomorrow. Hope it's a go.
Could take several trips to clear itself, (Awhile) or have it cleared with scan tool. Drive it several times to clear on it's own. Thanks let me know. P.S. The leaves are sucked in from the air snorkel, where the air is sucked into the bottom part of the breather housing.
Journey man you were right - air filter. It took about 150 miles but the engine light finally went out, whew. Thanks so very much. Never saw a rectangular filter before, you learn something new everyday!
Sorry you had to see all the BS going on around on this question. Like you said about your husbands vacation return, I have seen a lot of simple things fix a problem every day, but here we have a lot of know it all's looking to sound more professional than the common cense. Thanks again for letting me (us) know. Stay Warm.:-)
During normal operation the PCM tests the EGR valve for flow and if the VSV (vacuum switching valve) happens to be sticking when the test runs then the test fails and a code is generated. To run the test the PCM commands the valve closed which should result in an increase in manifold vacuum, and then the PCM commands the valve open which should cause a decrease in the manifold vacuum. The PCM makes this command several times in succession. With the VSV sticking the EGR valve does not close every time and that causes the PCM to set the P0402. Its important to note that if the valve is stuck open all of the time the system actually fails with a P0401 because the PCM doesn't know if the valve is open or closed.
You know you can stay away from my answers because you obviously don't know this is an electronic ECM and doesn't have a vacuum control and if the EGR was stuck open the engine wouldn't idle or run very good. So go teach your class and stop trying to impress yourself.
My mistake, I thought this site was all about helping people and open to everyone who wants to contribute. FYI it does use a vacuum operated EGR with a back pressure transducer. The VSV is on the left side of the engine and has pink/black and white/red wires going to it. (Confirmed Via Mitchell Pro Demand) Being back pressure transduced, the EGR can close at idle even if the VSV is stuck applying vacuum. The system also uses an EGR temperature sensor to detect flow and that can be monitored in scan data and a vacuum gage can be T'ed in to monitor for vacuum being applied to the valve assist in diagnosing a fault.