I'm not sure what the real problem is but I kept getting SES codes after I blew my cat out. When I scanned the car I got an Engine Gas Recycling code. So naturally I checked out the EGR. Tried to clean it out first. Still sucked so went and replaced it. Didn't change a thing code kept poppin in ocassionally. When I did the headers I pulled the 02 sensors out and they were White and Rusty looking...could that have been one of the problems? But in addition to that my cat was completely blown out? The wierd thing was that whenever I went to recheck the code it was never in the Code history...The only time the code existed was when the car was running and at the same time that it was on. But...the SES light always popped on at around 3KRPMs when I was driving steady for a while with the exhaust was at a moderate flow rate.

 

What year is your car? If your car is 96 or above, it has an 02 sensor after the cat, not before it, so it might throw a code if the cat is removed or not working.

 

95...seems to be sensitive to something.

 

I wish I could help you more, but ill try my best

My 95 ta stores the code, im not sure why yours doesnt.

EGR code can come from a bad oxygen sensor, or from high backpressure (if your cat is still there and its blocked, that could explain why it comes at over 3000rpm). It can get pretty complicated, eg. I heard even the coolant temperature sensor affects the EGR, but you would know if that is working or not.

A blocked vacuum line can also cause this to happen.

Ideally, you would need to find somebody who knows all the things that could cause an EGR code, and then know which of those problems are most common on and LT1, and then give suggestions on how to check for those... I really wish I could tell you something you dont know

I hope somebody intelligent reads this and responds and that your problem gets diagnosed and fixed.

 

there is a small sensor or soleniod located just to the right(when facing the motor from the front) of your EGR valve. make sure theres no visible signs to it b/c i believe its part of the EGR system. if you dont see anything wrong with it then theres a good chance you need a new one. hope somebody corrects me or agrees with me here b/c im not entirely sure about this.

 

Almost forgot to add. I did a vaccum test and everything was good. I also took the car to the Dealer and for once "they couldn't find anything." I even watched them read codes with the Tech2 and the EGR code wasn't even registering.

 

Exactly which EGR code did you get? DTC 32 (EGR recriculation) or DTC 27 (EGR solenoid)?


Assuming you got DTC 32 - An O2 senor can not cause or set an EGR recirc. code. High backpressure does not generally set an EGR recirc code. All the PCM does is look at the MAP sensor, to detect a "blip" in the MAP reading when it commands the EGR to open. If you have INADEQUATE backpressure, there will not be significant EGR flow, and the MAP reading won't change. A "blown out" cat can reduce backpressure in the exhaust to the extent that there is not enough EGR flow.

The unusual part is that the OBD-I diagnostic is not very sensitive and usually does not set a code, even if you remove the EGR valve. But in maybe 5-10% of the cars, the code will set. Maybe you just got "lucky".

 

32

 

I just put Jet-Hot LTs and a hooker y-pipe (!cats) on my car (OBD2) and now it's throwing the same EGR code as you (P0400 on OBD2). I can reset the DTC but it shows up again after a few minutes of cruising down the highway in 5th/6th gear.

"P0400 - EGR Recirculation Flow"

Question for you PCM gurus, on OBD2 does this DTC force the PCM into "limp" mode?

 

The term "limp mode" is grossly over-used. That is an operating mode that is designed to allow the engine run with almost total failure of the electronics. Few people will ever experience true "limp home". It is not the response to various trouble codes and sensor losses. In most cases, there is a default adjustment that the PCM can make to overcome the lost info input.

I doubt that anyone outside of GM knows all the intracacies of how the PCM responds to various problems. Logically, loss of the EGR system would result in the increased production of NOx, and increased possibility of detonation, under conditions which the PCM assumes to produce excessive combustion chamber temperatures. With no EGR to quench these temperatures, it would not be illogical for the PCM to pull some timing, or richen the A/F mixture. Does it do this? I don't know. That's why you either need to eliminate the cause of the EGR code, have the diagnostic turned off, or alter the conditions under which EGR operates, so that it is unlikely to be turned on.

 

Thanks for the detailed information Fred, I really appreciate you taking the time to explain the details.