How To: PCM and Tranny Pin thread

December 23, 2017

I'll put some schematics in here later on but I wanted to start this thread off with some close-ups of the plugs and show how to get to, identify, and remove / install pins.

Assuming this thread will be referred to most for adding 4T65 to 4T60 harnesses so the main focus will be regarding those 2 plugs but I'm going to get into a GM matrix style plug like C100 another day since a lot of those get re-pinned too.

First, GM PCM pins are common across a number of different plugs, we can see in this image a 3800 PCM plug, one from a '90's Vortec truck, and a 4XXX series tranny plug. I said 4XXX because the 4LXX rear wheel drive plugs are the same and would make a suitable donor for your 4T65.

So in theory we can salvage a Tranny plug and wires all the way back to the PCM (keeping the pins intact) from a number of different vehicles and shorten / lengthen the wires as needed but still have the pins pop right into our PCM.

PCM PINS:

So a typical PCM connector is going to have a dress cover along the back, it's held in by 6 barbs. On some early ones the dress cover will be the same but they will be barbed toward the inside. Those are easy to spot because they actually straddle the plug and hook along the outside.

The majority of these plugs are a metal body but there are some plastic bodies out there that I've seen.

I carefully grab the 4 clip portions with a pair of wire pliers and influence them toward the inside to release the barb while I pry it out.

These are fragile and if there's oxidization in the hole it's worth it to use a pick to clear it out a little or those barbed pieces will crack right off in there.

Then we have the 2 inside barbs, easy enough to release with my favorite little pick tool and the dress cover will fall right off.

So without the dress cover in place we can see the number that corresponds to each pin. A few seconds is all it takes to color with a sharpie marker and wipe a finger across the top and they can be read more easily.

The colored covers over the pins are TPAs, the ones on this plug are known as either "Clear" or "Gray" depending on where the schematic comes from.

The TPA has a little white barb and I use my little pick tool to push them in one at a time to slide it off and expose the pins. In this 3rd pic you can see how each pin is held forward by a little white finger of plastic.

That pin will slide right out of the plug without the TPA but if you're trying to salvage both ends of the wire you need to use a fancy release tool like my trusty little pick here to lift the finger while I rock and push the pin out the back of the plug.

Don't get too rough with these, those little fingers will break if you try hard enough. Once the pin is recessed back just an 1/8" or so it'll come out easy by pulling the wire.

Inserting pins can be a bit different, if there wasn't a pin in that hole already I just use something like my little pick to puncture the rubber membrane that's got the hole sealed before pushing the new pin in.

If the TPA DOES NOT SLIDE RIGHT ON WHEN IT GETS RE-INSTALLED don't force it, make sure everything looks good and just put a little pressure on it while you drag a pick down the little fingers. Once you find the one that's not seated all the way the TPA will slide right on.

Transmission Plug Pins:

Tranny plugs are fundamentally the same, the wires can go in or out through the front or back but it's easier to insert them from the back of the plug.

Before I take a Tranny plug apart I like to mark what direction the wires go for when the dress cover goes back on.

My little pick tool comes out again and the dress cover comes right off.

In these 2 pictures I'm showing that there's letters embossed in the rubber seal above or below each pin. Have to wipe them off to actually see it and again if the plug we're going to use doesn't have a hole in this seal a tool like my pick will make one.

Tranny plugs have a TPA of sorts, my little pick goes in and with a "pop" it comes right off so I can see the pins and the retaining fingers that hold them.

As with the PCM plug these pins will push right out right now but if I'm trying to keep the wire intact or operating on a harness it's attached to I'll use a safety pin or very small pick to release it and pull out out the back. It needs to be tilted in it's hole just a tad to be free from the molding of the inside of the plug before it will pull out nicely. I'm using my little pick for that in this picture because my thumb nail is too clumsy to get in there and influence it.

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Remember when you do a re-pin for a tranny and the schematics seem intimidating that all we care about is this part circled in the diagram for each pin. (DO NOT USE THAT DIAGRAM IT MAY NOT BE FOR YOUR APPLICATION).

For instance as long as we know that pin 28 on C1 of the PCM needs to go to pin D of the transmission plug we're good. It's nice to get that Tan/Black wire back in there rather than a random color so you can diagnose it more easily too.

This sample print is just one of 2 or 3 for a transmission, one of the prints will have a small key printed on it that tells which color PCM plug is C1 and which is C2 on whatever PCM we're on.

Adding a 4T65 is going to require a connection to ignition power, you can solder onto the old power wire off the 4T60, also there may be a low reference that shares a wire from the PCM with other sensors, when that happens just bare a little spot on the wire and solder it to the existing wire in that location on the PCM. Looking at my sample diagram this particular PCM has that low reference on plug C1, pin 56.

Hope somebody finds this useful, party on!

Edited December 23, 2017 by Imp558

2 Vehicles · December 23, 2017

Promoted to FAQ.

December 23, 2017

Awesome write up imp! I'll definitely be using this

December 28, 2017

This is typical construction for a GM Matrix connector such as C100:

Notice the comb on the sides is the pin lock, it needs to come out first and pries out easily as long as you pull it evenly:

Take a minute and play with the lock in an unused cavity, get familiar with how it moves and holds the pin:

Carefully pick the lock away from the pin to be extracted and move it away.....

In one movement bring the pick upwards while it's holding the pin back and use it to pry as well to start the pin out the back. I'm like really good at it, if it's easier to use a second tool to push your method may be a little different.

i'm not going to get into inserting pins, there's nothing about it tthat's tricky.

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Here's a typical 4T65E-HD, should find this until 2001:

A common harness to re-pin for the first gen is 1996 Regal, the 4T60 plug has an ignition power and sensor low ref you can recycle when wiring the 4T65 in:

And here's the 1996 Regal PCM:

Edited February 19, 2018 by Imp558

December 28, 2017

Doing all the Regals first because I'm a biased Prick and not ashamed to admit it.

This is up to 2003 with the exception of 2001 which I don't appear to have:

1997 Regal: