I'm trying to diagnose and fix the PO400 CEL code on a 96 obs 2.2L.

 

I need to buy a manual... :-\

 

What is this thing? With this thing removed, the larger diameter hose that attaches to the bottom of it spews out water droplets when the engine is running. When it's back in place and the hose is hooked to this thing... a substantial amount of water ends up going up inside it. With this thing removed, I tap the bottom nipple on a hard surface and water comes out.

 

Is this normal?

 

Second question....When sucking on the vacuum hose that connects to the EGR, the idling engines RPM drops slightly and it runs rough. This indicates that the EGR is working as it should?

 

 

That is a Pressure Differential Transducer.

I don't believe there is really anyway to test them.

 

No, there should not be water in it or the lines going to it.

 

Yes, if you pull vacuum on the EGR valve while engine is idling, the idle speed should drop, run rough or die.

thanks WA.

 

Now the question is... why are there water droplets bubbling out of this hose and could the transducer being full of water cause my CEL code and terrible gas mileage (14.5mpg).

I would say that water in the PDT could very well be the cause of your P0400 code.

I don't think it is the gas mileage problem though.

 

The cause of the water is the big question. It has to be condensation, I would think.

 

I would disconnect all the vacuum and other related hoses and pipes. Blown them out with compressed air. Make sure all vacuum lines are good, and properly routed and connected.

 

Probably wouldn't hurt to give the PCV system a good look.

 

What have you done to address your fuel mileage problem if anything?

Yes that is the egr backpressure transducer. There's a good article on endwrench about the P0400 code - http://endwrench.com/images/pdfs/Emissions.pdf

It says "The transducer can be checked with a pressure pump, but there are no specifications for exactly when and how much it should open for a specific pressure."

I haven't done anything particular to address the MPG except a new air filter. I kind of assumed that the low MPG was a byproduct of the EGR issue. I was hoping that fixing the EGR would result in getting normal MPG again.

Yes that is the egr backpressure transducer. There's a good article on endwrench about the P0400 code - http://endwrench.com/images/pdfs/Emissions.pdf

It says "The transducer can be checked with a pressure pump, but there are no specifications for exactly when and how much it should open for a specific pressure."

 

I've read that article a few times and even printed out to take outside to my car.

 

It talks about heat and carbon build up possibly damaging the transducer making the diaphragm not work correctly. I have to think that water would also make it work incorrectly.

 

I'm remembering that about 2 weeks ago I cleaned the engine bay of the suby with a hose. Basically spraying water everywhere in the engine compartment. Hmmmm,,, That must be where my water problem came from!. MY CEL CODE SHOWED UP SHORTLY AFTER I DID THAT! Doh.

Yes I'm not sure. Maybe it is condensation.

 

"Metal pipes dip below the throttle cables. Condensation may form in this area, causing corrosion on the inside of the metal pipes. If this corrosion is allowed to get bad enough, it may block the flow of vacuum through the pipes and trigger a DTC P0400. Remove the vacuum hoses from the pipes, then blow through the pipes with compressed air to make certain they are fully open."

I actually routed new vac hose around those metal pipes a few days ago. The engine runs fine without the transducer. Maybe I'll drive it around and hope all the water gets out of the system.

 

There's quite a bit of water coming out of the tailpipe too.

Does the CEL go out once you've fixed the problem or do you have to make it go out manually by unhooking the battery or getting someone to reset the CEL?

 

thanks

You might have a similar problem to what I caused - I pressure washed the engine and knocked off the EGR hose at that same connector.

 

Once I put it back on and reset the computer (disconnect battery for 5 to 10 minutes) the code went "away".

 

The engine will run rougher without the EGR and tends to heat the peak exhaust temps a bit as well.

 

But water in it...hmmm...

...checked all the vac hoses... drove it for a while today without the transducer. I think all the water is gone now... didn't see any bubbling out of the hose or the exhaust after I got home. Hopefully, it's all gone. I put the now bone DRY transducer back on and am hoping for the best. I'll reset the code by unplugging the battery and see if it comes back on.