Catalytic Converter/Tranny/PCM

SimplyRAD · March 7, 2005

Does anyone know if the catlytic converters "always" throw a code? I have a 2001 8.1 with the allison transmission. I think the Chevy Dealership is not wanting to replace my cats under warranty(state law).Something is not right and my truck losses its gears while I am driving. Tranny fluid looks fine, and I only have 31K miles on it.

I believe the loss of power in my truck is due to the cats "pluggin" the engine up. Then the pcm trys to adjust itself while I am driving.

I have no codes registering in the ECM/PCM although, the Chevy Dealership say I have a code P0700, they try to clear it and it flashes on and off.

Please tell me if my thinking is wrong. I am willing to pay an additional "tranny diagnostic" just to see if the TCM is fouled up.

HDCrew4x4 · March 7, 2005

Don't know if the cat always throws a code but...

I had a similar catalytic converter problem on a 97 dodge. The converter basically "plugged up" and you had to floor it to get anywhere once it started really getting blocked. They switched out the catalytic converter and it was like brand new. I'd guess I was around 40k miles when that happened. The dealership blamed the gasoline I used. Don't know the chemistry of what causes it - but I never had any problems with it for the next 60k miles I drove the thing.

GM-Tech · March 7, 2005

Does anyone know if the catlytic converters "always" throw a code?
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Not necessarily. But your problem doesn't sound like a clogged cat. They generally get worse and worse until the vehicle runs so bad it won't even move.

The TCM sends a class 2 message to the PCM requesting the MIL to come on and it sets a P0700. In other words, that DTC is saying, "Hey, look in the TCM to see why this was requested." There SHOULD be a DTC in the TCM.

But I'm a little confused with your description as to what is occuring. You said the "truck losses its gears while I am driving." and I'm not really sure what that means, but then you say the truck loses power. Sooooo, do you have a tranny problem or an engine problem? Or is it not that clear?

Scyry · March 7, 2005

Think he means he has so little power that the tranny is down shifting (loses a gear)?

So you are thinking you either have a loss of power due to the cat being plugged and this causes your tranny to down shift to make up for the loss of power. Or, you are thinking the tranny is slipping, causing a loss of power and the trannny is down shifting to try and compensate?

SimplyRAD · March 8, 2005

Does anyone know if the catlytic converters "always" throw a code?
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But I'm a little confused with your description as to what is occuring. You said the "truck losses its gears while I am driving." and I'm not really sure what that means, but then you say the truck loses power. Sooooo, do you have a tranny problem or an engine problem? Or is it not that clear?

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First incident, had to floor the pedal to get any movement, all gears including reverse. Let it sit overnight, no problem.

Second incident, happened this morning. While driving about a quarter mile of getting onto the freeway, Everything on my cluster started to flash. Didn't kill the engine but lost my tranny. There was a no go when I stepped on the pedal and I just reved the engine. I then merged off tried different gears and nothing not even reverse. So, I am thinking computer related, shut off, so I can manual flash the ECM using ignition. Works, goes back into gear like new and I drive it straight to the dealer like nothing was wrong.

I am still thinking I have bad cats. I also think something is wrong with the TCM. I haven't heard back from those mechanics.

SimplyRAD · March 8, 2005

Think he means he has so little power that the tranny is down shifting (loses a gear)?

So you are thinking you either have a loss of power due to the cat being plugged and this causes your tranny to down shift to make up for the loss of power. Or, you are thinking the tranny is slipping, causing a loss of power and the trannny is down shifting to try and compensate?

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First Incident, yes, little power, felt muffled, but changing gears fine. I couldn't feel the downshift no SES.

Second incident, somethin went wrong cause it made me pull over.

There are no unusual sounds in the tranny. Definately electrical at this point in dealing with the tranny...

GM-Tech · March 8, 2005

Second incident, happened this morning. While driving about a quarter mile of getting onto the freeway, Everything on my cluster started to flash. Didn't kill the engine but lost my tranny.

If that ain't an ignition switch problem, I don't know what is.

HDCrew4x4 · March 8, 2005

It's good to have GM-Tech around, eh? This place is awesome!

dewfpo · March 8, 2005

Your cats don't plug and then unplug like you describe so it "ain't" your cats.

DEWFPO

SimplyRAD · March 8, 2005

Your cats don't plug and then unplug like you describe so it "ain't" your cats.

DEWFPO

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I am open to suggestions. what's inside of these cataltic converters? They are rewally expensive..

SimplyRAD · March 10, 2005

Second incident, happened this morning. While driving about a quarter mile of getting onto the freeway, Everything on my cluster started to flash. Didn't kill the engine but lost my tranny.

If that ain't an ignition switch problem, I don't know what is.

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I am going to change the batteries. These mechanics believe the TCM looses its voltage. I do have some corresion around the terminals which keeps coming back after brushing. So I'll start with the new batteries and then go from there. I haven't had any incidents occur after getting the truck back and they say the cats are fine.