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The Dreadful P0401 Code

1321 Views 21 Replies 5 Participants Last post by  dezldave961
I have 2001 Impala with a 3.8L engine with no modifications. The past few months my check engine light comes on with the same P0401 code. I disassembled the intake system and replaced the intake manifold with a new gasket, cleaned the throttle body, and the MAF sensor. The car runs fine when in the warm-up phase. When driving the car at operating temperatures below 25mph I don't encounter any issues (driving through the neighborhood). But, when I get on the roads or highways above 30 mph the CEL comes on when I slow down below 30mph. So, I read multiple threads about cleaning the exhaust tube to the intake (not clogged). I cleaned the EGR valve with throttle cleaner and let it soak overnight. I put the EGR on the following day and started the car and decided to drive it on the highway. I didn't see any codes and the car was running like it was 2001 again. The next day, I went to start the car and got a CEL with a P0403 and P0405. Popped the hood, and noticed I forgot to plug the EGR back in. I cleared the code and drove around again, the same d**n P0401 code reappeared. I know I can't pass inspection without a operating EGR and the CEL on. Is it a good chance the issue will be resolved if I just purchase a new EGR valve?
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Might want to try soaking the valve in PB or WD next time it's cold, just to make sure it's not a movement issue internally.

I know this doesn't help: but I hate 3800 EGR and eliminate it as often as I can, since it's useless and barely does anything for emissions, while causing thousands of people these kinds of issues which tend to increase emissions while diagnosing.
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I'll try that. I was thinking about deleting the EGR, but from what I understand it would require engine tuning. Plus, I would never pass inspection.
The tune is required for full removal to disable DTC's, but you can "quiet delete" by capping the exhaust manifold side & just let the EGR pipe not pull dirty/hot exhaust into the intake. Can be done for free, and if you do it right, passes visual inspections, too.
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That sounds like an option. Do they sell caps for the exhaust manifold? Or, will I need to have it welded shut?
You can do it with a properly sized coin, ensuring it won't move in either direction when you bolt it back up. Using a chunk of block-off wouldn't pass a visual check.

All depends on how you want to do it. Dig in and get a feel for the project. You may need to trim the tube some to complete everything.
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Thank you for this information @dezldave961
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The tune is required for full removal to disable DTC's, but you can "quiet delete" by capping the exhaust manifold side & just let the EGR pipe not pull dirty/hot exhaust into the intake. Can be done for free, and if you do it right, passes visual inspections, too.
Can you get the same results by blocking the input on the EGR valve?
Maybe, but if you get in the way of the pintle movement, it'll be mad. Letting it move as it wants, but not have hot exhaust crud coming into the intake is the preferred method.
P0401 is insufficient flow. If the passageways are clear, than you have two culprits. Either the tube/gaskets are leaking or the EGR valve has failed. Check for leaks, if none replace the valve.
Before running to replace it, there's no harm in hosing down the valves moving internals to possibly free up movement (TB cleaner spray, etc.). The EGR is a dumb system (solenoid to open/close, and position sensor to track where it is), nothing actually checking airflow, which is why the DTC can be somewhat misleading.
Maybe, but if you get in the way of the pintle movement, it'll be mad. Letting it move as it wants, but not have hot exhaust crud coming into the intake is the preferred method.
If I use the nickel method, will that prevent the check light from coming on?
If I use the nickel method, will that prevent the check light from coming on?
I would not block it off or disable it. Having a working EGR is critical to emissions as well as lower cylinder head temps. You said you replaced the intake gaskets? Cleaned the EGR and passageway? I would go over everything you've done and make sure there is nothing left loose or leaking. If you can get a smoke machine I would do that and check for leaks.
Hahaha, who's paying you to drink the koolaid?... EGR on these cars is a joke and box check when they were inventing random things to say they tried. It provides no tangible benefit while nibbling part of cyl 6's exhaust, besides introducing excessive heat into a failure-prone region of the intake manifold. The efficiency of this engine and the waste spark system of the coilpacks is much more beneficial to the SULEV rating later 3800's got without gimmicks like EGR or AIR being tacked on (thankfully, they didn't slap DoD/AFM on them, because that's been detrimental to rings/lifters in LS's for years now).

Diagnose the issue, most likely a leak or stuck EGR valve, and figure out what makes it return to good working order before attempting tweaks.
Hahaha, who's paying you to drink the koolaid?... EGR on these cars is a joke and box check when they were inventing random things to say they tried. It provides no tangible benefit while nibbling part of cyl 6's exhaust, besides introducing excessive heat into a failure-prone region of the intake manifold. The efficiency of this engine and the waste spark system of the coilpacks is much more beneficial to the SULEV rating later 3800's got without gimmicks like EGR or AIR being tacked on (thankfully, they didn't slap DoD/AFM on them, because that's been detrimental to rings/lifters in LS's for years now).

Diagnose the issue, most likely a leak or stuck EGR valve, and figure out what makes it return to good working order before attempting tweaks.
No Kool aid man, I'm a master tech so I know these systems very well. There's a reason it's there, auto engineers discovered it by accident that exhaust gas was found to cool the cylinder heads as well as help with emissions. This isn't the 70s where it was a crappy mechanical valve, this is a computer controlled system. He's not doing anything high horsepower so why run around and do tricks? It's an integral part of the system, why compromise it?
Yes, when I was in the manuf. side of things as an engineering undergrad in Flint and Detroit 20yrs ago, the theoretical side of things always sounded great. The practical application, especially the 3800's version, is much more detrimental than beneficial, as reflected by the much higher prevalence of failures induced (especially in the L36 UIM's and gaskets), while combustion burn rates aren't in need of NOx assistance with the variability of timing advance and AFR with modern engines able to counter the issues EGR thought it could solve pre-EFI.
Yes, when I was in the manuf. side of things as an engineering undergrad in Flint and Detroit 20yrs ago, the theoretical side of things always sounded great. The practical application, especially the 3800's version, is much more detrimental than beneficial, as reflected by the much higher prevalence of failures induced (especially in the L36 UIM's and gaskets), while combustion burn rates aren't in need of NOx assistance with the variability of timing advance and AFR with modern engines able to counter the issues EGR thought it could solve pre-EFI.
I am stumped. I replaced the EGR, checked for blockages, checked the PCV. When I erase the CEL, it comes back on in 2 to 3 days of driving. At no time does the engine run rough, always smooth. At this point, i would prefer to delete it, but don't know where to go to get the code removed from the ECU
I am stumped. I replaced the EGR, checked for blockages, checked the PCV. When I erase the CEL, it comes back on in 2 to 3 days of driving. At no time does the engine run rough, always smooth. At this point, i would prefer to delete it, but don't know where to go to get the code removed from the ECU
No other codes? Did you check the passageways in the throttle body? Pull your oil filler cap off. If you hear a sucking sound your PCV system isn't working. Just had this happen to a friend that caused a p0171 and p0401. There's an oring around the pcv valve that people don't know about that disintegrates over time and creates excess vacuum in the crankcase. If that all checks out, check the connector at the EGR and make sure your getting power, ground and signal.
I have done everything except checking the connector. Where can I get the info on that? Also, I was going to remove the exhaust tube just to check it out, but it looks like the bolt head is missing.

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I have done everything except checking the connector. Where can I get the info on that? Also, I was going to remove the exhaust tube just to check it out, but it looks like the bolt head is missing.
Off the top of my head red should be power, black should be ground but I can't remember what color the signal wire is. I would just check and see if you see a voltage of around 4.5-5 volts, that would be the signal. That sucks about the bolt head.
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