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Old 08-18-2022, 07:27 AM   #21
RH45
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Default Re: Saturn SL P0401

I have a 2002 SL1 that threw a P401 code about 100K miles ago. I replaced the EGR valve with a "Standard" and all has been well until a couple of months ago. I tried running a cable through the ports, replaced the EGR valve, and tried running it with the EGR valve off. When running with the EGR valve off, it did NOT rev up. although I didn't try to put a vacuum gauge on the intake port, I could feel vacuum, and I could feel exhaust coming out the other port. This car doesn't have a MAF sensor, so I really don't understand how it reads flow. Just for kicks, I replaced the front oxygen sensor, thinking it might be a little slow. Since I put the newest EGR valve on it, I get, and have to clear the code every day, but, it seems to be running just fine.
This check engine light is just annoying.
Anybody have any ideas??
Thanks!
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Old 08-18-2022, 08:19 AM   #22
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Default Re: Saturn SL P0401

Quote:
Originally Posted by RH45 View Post
This check engine light is just annoying.
Anybody have any ideas??
Thanks!
I did the cable clean out trick. I got black tar-like crud on the cable. I also found the PCV valve old and all gummed up. I'm convinced the entire intake manifold is clogged with tar from the oil fumes. I'm going to pull mine off and do a complete deep clean inside every passage. It's a big job, but I think the problem is just going to come back again unless the clean out is done properly.
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Old 08-18-2022, 07:08 PM   #23
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2003 L-Series 3.0L Sedan
Default Re: Saturn SL P0401

RH45, search past threads in these forums with P0401 errors. Examples are at the bottom of this page. P0401 is the engine exhaust gas recirculation (EGR) valve not flowing enough recirculated exhaust gases when it is commanded to open the flow of gases into the intake manifold.

When the egr valve is removed and engine started, the intake port should feed unfiltered air directly into the intake manifold and rev the engine (to factory programmed rev limits) immediately. Not doing this means the intake manifold port is blocked with excessive exhaust carbon byproducts. The exhaust port may be blocked too as exhaust should be blowing out this port freely with the engine idling.

The mass air flow (MAF) sensor measures air flow volume in grams per second for EFI systems using it as improving EFI performance and better emissions control. It does not directly contribute to generating P0401.

The upstream O2 sensor (on the exhaust manifold) measures oxygen content in the exhaust stream. The egr valve meters exhaust gases into the intake manifold during acceleration and cruise speeds. No exhaust gas flow at idle or wide open throttle. Exhaust gases mixed into the air/fuel mixture reduces combustion temperatures. Oxygen measurement by the O2 sensor is used by the engine computer to fine tune fuel mixtures to control emissions. A programmed range of depleted oxygen during combustion is compared with egr operation when (more or less) oxygen is measured is determined by the engine computer of egr operation. This is how the P0401 error code is generated, insufficient exhaust gas flow into the intake manifold as the O2 sensor measures combustion gases.
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