P0700 and P0877 while towing heavy and typically uphill

R

Rooftop Special

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Sep 19, 2012
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Hey Guys,

Had a p0700 which is a generic code I know. Every time it happened was when I was towing heavy and typically uphill. I kept resetting the CEL via my CTS so I could keep going not realizing it would "reset" on its own.

I chased cheap fuel pressure fixes as I couldn't read the code that tripped the P0700 and I thought I had a fuel pressure issue during max demand.. Yesterday I'm hauling a heavy load of stone and it throws the p0700 when I'm pulling into the driveway. Now I leave it alone and O'Reillys scanner actually pulled the p0700 and now the p0877 (Transmission Fluid Pressure Sensor / Switch D circuit low.

I've had the truck 4 year and when I bought it I had a transgo jr with deep pan installed. Other than that the tranny is stock.

Where should I start?

Thanks in advance!
 
Mike L.

Mike L.

Got Sheep?
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Need mileage, does it have a programmer, what do you do with the truck. I don't know why some of you guys think we can wave a wand and diagnose with no info.
 
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R

Rooftop Special

Member
Sep 19, 2012
47
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Thought I was somewhat clear on what I do, "towing heavy when it acts up and typically uphill". It's done it towing 17k and done it towing 28k. It doesn't act up empty or even hauling 3200lbs in the bed. I know I'm towing over ratings. If the answer is "I need a new truck", or "time to get the tranny done", that is fine. However I have nothing that feels like slippage or high tranny temps. It literally runs great then BAM. I doubt beat on it going up hills obviously she's working because of the weight.

Truck has 240k but I rebuilt engine 40k ago. Running Idaho Rob standard tunes on #2. Don't ever run higher than #3 and that's only when empty.

Thanks again,
 
R

Rooftop Special

Member
Sep 19, 2012
47
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Still playing hell with this. Changed the 20 pin pass through connector on the tranny as it was leaking and I thought it might have been shorting. Also changed the PSM, no dice.

It's always went into limp mode with the p0877 code while towing and it does it so inconsistently.

Any thing else I should try?

Thanks,

Casey
 
R

Rooftop Special

Member
Sep 19, 2012
47
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Thanks for the info Ron. Ended up taking it to a shop. They can't figure it out and says everything "looks good".

I have no damn idea what to do now.
 
R

Rooftop Special

Member
Sep 19, 2012
47
1
6
I honestly wouldn't be opposed to that. I would crap little green apples if it did it after a build though. Don't you think if it was electrical it would be more consistently doing it? Is there something mechanical that can be causing a pressure issue on that switch?

I've read of a couple guys having low fluid or the sump filter sucking air that caused it but all were consistent issues not like mine when it only happens during towing.

Not getting any other tranny codes though like slippage, etc.

If I was back home in Phx I'd just run it out to you Mike and let you have at it. I'm in Montana now but have to get this figured out before we attempt to head home in a couple months.
 
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