Help please.....I have a 96 Monte Carlo Z34 and I need to get this problem fixed asap as I cannot pass NC inspection.....Back in July a month before my inspection was due I completed a tune up and charged my ac system to finish out the summer. MIL was reset before a test run and almost immediately while going no more than 5mph the MIL illuminated for PO401(insufficient egr flow) and PO402(excessive egr flow). Now I'm mad because the only codes before the tune up were for random misfire and secondary air injection. The random misfire code was solved by replacing all spark plugs, wires, and coil packs. And the secondary air injection code comes and goes. Now to resolve the egr codes I started by cleaning the maf sensor with CRC QD contact cleaner which I bought from walmart. Then removed the egr valve and cleaned it and the pintail with carbon cleaner. Finally I ran seafoam through the throttle-body. Okay I replaced everything started deMonte and reset the MIL. Next test run went very well and at the end of the test my car was ready for inspection. So I thought.....while driving to an inspection station the MIL comes again but only for PO401. At this point I'm furious. I drive to autozone just to spend 150 dollars on a new egr valve although I'd been doing research and most people were saying that this wouldn't solve the problem.....Well I had to try and at least I got my money back.....So cleaning the egr valve and pintail, cleaning maf sensor, running seafoam, and replacing the egr valve but still have PO401.......Any input will be greatly appreciated.....

 

Maybe an accumulation of carbon in the intake is obstructing flow?

 

My FIRST thought is take the EGR off and clean the tube/tunnel that connects the EGR to the plenum or LIM.

On the 3100 engine, the 3 solenoid EGRs were known for building up carbon deposits and generating CELs. Some carb clean and something to chase through that tunnel and see what happens (once or twice, I had to pull the throttle body off a 3100 to better get to the blockage).

But if the flow is not right for the EGR, that's your best starting point, make sure it's not restricted.

 

Okay guys I thought I explained this well enough....Egr valve has been removed and cleaned and I have also ran seafoam through the throttle body-intake.....that's as clean as it will get.....any other input besides someone saying carbon build up will be greatly appreciated......Oh and as stated before I have a 96 Monte Carlo Z34(3.4 dohc)

 

Unfortunately, I am not familiar with the 3.4 DOHC. So I'm applying what I know about other related GM engines.
So, the tube between the EGR and the UIM or LIM is clean?

You may have an issue with the EGR. Is your EGR a 3 solenoid EGR? I know GM has used this style EGR on a LOT of different drive trains from the late 80's to mid-90's. If it is, then I know you can dis-assemble and re-assemble the EGR. I found on two 3 solenoid EGRs sometimes the plungers on them gum up and won't move. Also, the holes plug up. Disassemble, spray with carb clean and use a wire brush to clean it up. Re-assemble and pop on the car.
FYI - The 3 solenoid EGRs have about 3 layers, a base, middle and top (top is the solenoid housing). They may look like they at symmetric layers (meanings as along as you have top and bottom of each layer facing the right way the rest does not matter). They in fact have ONE proper alignment. Otherwise you may get 1 or 2 screws in to re-assemble and wonder why the last does not line up right.

Outside of that, follow the EGR flow of the EGR. What tubes and devices connect to and from it? What else in that system may be malfunctioning.

 

Well all 90 and later engines except the 2.5l and 94-96 3.8 use the digital EGR valve....I've attached a link for a picture of when I installed the new valve and the old one is sitting on the intake plenum. I still don't understand why a brand new valve would still allow for the same code. Anyway I'm off to tackle this task again.....http://www.facebook.com/photo.php?fb...type=1&theater

 

Unfortunately, I can't view your facebook link.

As for the use of digital EGRs, I know GM used the 3 solenoid EGR on the '94 and '95 3100 v6 (such as I've wrenched on '94 and '95 3100 powered Grand Ams with it). But I don't know how much longer past that they used it and on what drive trains.

Sorry my suggestions are not worth while on this one.

Another thing you may want to inspect is the wiring to the EGR, make sure a rodent didn't crawl in and gnaw on them a little. Best of luck.

 

I have had an 03 now a 03 ss and 04 supercharged and I am fed up with these piece of ****s. I am getting p0401 code I tried everything but no fixes. Should drive it off a cliff. I will never get another one.

 

Code P041 is a down stream O2 sensor. Here's a link to the code and possible solution's https://www.obd-codes.com/p0041 Good Luck

 

I get a po420 code so I replaced cats two times and still pulls the code. So I replace egr vavle thinking that was the problem was it. Since I replaced the egr vavle with teo new ones now a code p0401 code pulls up. I clean the tubes an the egr ports and throttle body and still pops up codes for egr vavle within five mins of driving. If I put old one on car it doesn't pop up the p0401 code but starts to pull the p0420 code again. I have a new map sensor and a whole new vacuum harness. Really getting feed up on this car. I also have both o2 sensors replaced.