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P0404 code on 2005 Lesabre

P0404 code, 2005 Buick Lesabre- the old Buick’s been intermittently throwing a CEL. It’s been coming on and then going off, but now the light’s pretty much staying on. I had the code read, P0404. I suspect the EGR valve, as it’s been very mildly bucking at light rpm when cold lately. Is there any way to test this type of EGR valve? I’m more familiar with testing EGR valves on old TBI 350’s, but this one appears totally electronic with no vacuum lines, so no testing to see if it holds vacuum I assume. Also, I tried cleaning around the pintle and where it seats. We’ll see if that helps, but I doubt it.

Read all about it.

https://www.obd-codes.com/p0404

Tester

Thanks for the link. It would seem that I need a scan tool to really check that type EGR valve, which I unfortunately don’t have. We’ll see if my attempt at cleaning removed any carbon. I didn’t experience the light bucking or stalling when I drove it after attempting to clean around the pintle area, but the engine wasn’t completely cold (only condition I’ve noticed it). I guess I’ll either get lucky or it’ll get worse.

Well, after cleaning egr valve pintle and seating area with brake parts cleaner and a little light scraping, the cel has gone out on it’s on after a couple of drive cycles. Here’s to hoping I got lucky with my cheap, shade tree shot in the dark.

Ahhh, the cel came back on today. Nuts! Still, cleaning the egr valve did make the light go out for a couple of days, so there must be a connection. I believe I’ll gamble on a free to me scrap yard unit when a car with a compatible engine arrives. Do a little egr swapping and see what happens.

I suspect I might have a really small exhaust leak, although I haven’t been able to pinpoint it. Could this case the error code, I assume?

It’s possible you could clean the existing EGR up enough to get things working again by removing it and doing a bench de-gunking. I replaced the EGR in my truck recently, and those things are quite expensive.

I did try to clean it, and the cel went out. Then came back on after a couple of days. And is off again now! I’m not terribly concerned as I don’t think it’s a huge deal. Check engine lights being on is a pet peeve of mine, like most guys here probably. The light is still off for now. It’ll probably be back!