Low range for GM PCM

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cpfeifffer
Posts: 81
Joined: Mon Nov 26, 2018 6:03 am

Low range for GM PCM

Post by cpfeifffer »

Good afternoon!

I need to get my low range sorted out. I have installed a 2006 GM 5.3L with 4L60E.

Currently, whenever I shift into low range on my TC, the PCM gets a different speed than it expects and throws a P0894 code. It also doesn't shift properly.

How have you guys gotten around this? I have found the terminal on the PCM for the 4WD Low signal (C2-16). See below.
Transfer Case (GM).jpg
Is this looking for a ground or some other voltage?

Also, how do you account for different gearing of the transfer case? I think the GM case was 2.72:1 and mine is different.

Thanks for the help!

Charlie
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1978 Cherokee Chief
5.3L L33, 4L60E, Atlas II 5.0
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Yeller
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Location: Rogers County Oklahoma

Re: Low range for GM PCM

Post by Yeller »

The only way around this that I am aware of is to use this transmission to transfer case adapter with the speed sensor in it. With a 2.72 low range it can be wired around to work with a switch but with your 5.0 atlas you have to use this adapter from Advanced Adapters. It make the ECM believe it is a 2wd transmission no matter what range the transfer case is in. You will still have to run the speedometer off of the transfer case for it to be correct in low range.

https://www.advanceadapters.com/produc ... apter-kit/
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tgreese
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Re: Low range for GM PCM

Post by tgreese »

This seems like something that could be hacked if you map the transmission connections. Somebody figured out a way to make this work.

I would compare the connections 2WD vs. 4WD. What do they do with C2 on the PCM is there's no transfer case? Maybe grounded through a resistor (ie pulled down constantly but not a short)? Or a jumper in the PCM? And what's the dotted line between A1 and C1? I presume this means they are on the same plug.

I expect this will take some time to figure out. You're on the right track asking on the various 4WD forums for some hints. This seems like something they would have covered on Pirate previously. Be sure to search and read first on that site before you ask a (potentially naive) question.
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Yeller
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Re: Low range for GM PCM

Post by Yeller »

I know a few professional swappers that are very adept at ecm/pcm programming and wiring. They both say with a 4l60e the adapter with the speed sensor is the only fix unless you are running the original transfer case that came behind it. There is no output speed sensor in a 4x4 4l60e, it uses the one on the output of the transfer case and no way to correct the math for a non original transfer case, a speed sensor has to be added.
The bus I ride is so short it is a yellow Smart Car full of squirrels, monkeys and clowns.

1970 J2500 Resto Mod
https://www.fsjnetwork.com/forum/viewt ... 12&t=21395

1974 Bronco “Broncno”
https://classicbroncos.com/forums/threa ... st-3411909
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