Code 55 and 56 - what causes these?

[Black88GTA]

This just started happening this past week. It's happened twice now.

When I start my car cold, it'll idle good for a bit (~30 seconds) and then the idle drops real low (the car has never stalled though) and the check engine light comes on. Once I get moving, the light goes out and the car seems to operate normally.

I got around to checking the stored codes today, and I came up with code 55 and 56 - "EGR Temperature sensor or circuit" and "EGR system" respectively. The obvious answer would be to look at the EGR temperature sensor , but is there anything else I should inspect that might cause these codes to pop up? Also, where is the EGR temp sensor located, and is it easy to get to it?

I should also mention that this car has gotten dismal gas mileage (~13-14 mpg around town) ever since I got it in February - could this be related?

[Manarius]

Are you running the A/C a lot? That would contribute to your poor gas mileage.

[Black88GTA]

Originally Posted by Manarius

Are you running the A/C a lot? That would contribute to your poor gas mileage.

I haven't used it hardly at all. I prefer driving with the windows open whenever possible...

[SoCal LS-L]

Im in the same boat man, ive had the 56 since I bought her. After I cleaned out the EGR pintle and vacuum lines, the MIL stayed off for about 4 days and came back. My idle also drops pretty low after it warms up... about 350-400 RPM. I would say that your EGR sticks open momentarily, could be a restriction in one of the vac lines or solenoid. I still need to check and clean my solenoid, since I cleaned everything else already. Im not really sure about the temp sensor though.... ill keep an eye on your thread to see if anyone can field that..... im still wondering how the computer can sense an EGR valve stuck open/closed condition in the first place (no sensor on the EGR itself).

[SoCal LS-L]

Just wanted to shout out in triumph that I FINALLY got rid of my EGR code and the accompanying MIL. My EGR vacuum diaphragm was toast, so replaced that... code returned immediately along with a new code 55. Went back over what had been screwing with me before, a clog in the hard-line that runs under the intake. No matter how many times I would free it with compressed air, it would be clogged mysteriously the next time I checked, every time.

Soooo this time, i just bypassed the hard-line completely (its the one that does NOT go to the solenoid, just straight to the modulator) and ran a vac line from the TB port down to the modulator. PRESTO! (albeit looks like crap )Cleared codes, drove all day, NO MORE FRIGGING BRIGHT GLOWING SERVICE ENGINE LIGHT!! Of course, the only reason I dove into it after all this time was because its smog check time

Wish me luck... I poured "Guaranteed to pass" in the tank, so its a sure bet right?

[Sean486]

That's awesome! Your persistence finally pays off. Hopefully this information will help the next guy struggling with a EGR code. How do you think the vacuum line will hold up compared to the hardline? I am assuming there was a reason they used a metal for that one.

Good luck with your smog inspection!

[SoCal LS-L]

Originally Posted by Sean486

That's awesome! Your persistence finally pays off. Hopefully this information will help the next guy struggling with a EGR code. How do you think the vacuum line will hold up compared to the hardline? I am assuming there was a reason they used a metal for that one.

Good luck with your smog inspection!

I think it was just for appearance than anything else.... the new rubber line doesnt look nearly as "neat". Whatever is in the metal line is made of kryptonite as no amount of brakeleen and compressed air could tame it.

[Suby Fan]

there is a kind of parts washer that i use that works extremely well i forget the name of it but its at any parts store and its the kind where you let parts soak for a while.