Ecm Pin Diagram For 1998 Chevy Truck

Next Locate the Red Plug in. It will say red and have a red cover

Again through these pics ignore my SHINY Blue wire it was a failed attempt at something else.
Now on the back of this RED plug in you will have to again unsnap the back taps to see this and Locate PIN 26

It will be open with nothing in it. If you bought the kit #12167310 You paid $50 for a jumper wire that will simply plug into this open pin and PIN 18 the Pin you made open on the WHITE, GREY or Clear plug in. Remember the spot you took the Black wire with a white stripe out of. It is now open as well. Now instead of paying $50 you could do like I did. Run to you local U-pull it and cut a few Ends off a wiring harness off any GM vehicle with the same pins and make your own jumper wire. Like this

I recommend using solder on any cuts and connections you make I used a Butt connector only to verify it worked.
Now Pug one end into PIN 26 on the back of the Red Plug and ensure it goes in Flush

Snap the Red connector Back in at the top. Do the Same thing on Pin 18 from the WHITE GREY or Clear connector. You will now have a Wire that Connects PIN 26 from the Red Plug in to PIN 18 on the WHITE, GREY or CLEAR plug in.
Its best to push the connector in through both the back of the Black plastic and Green gasket. Just like the factory wiring

Again use a small finish nail clear the way if your having problems. Now zip tie all wire together PUT Di-electric grease on all the plug in removed and plug in everything.
Be sure RED goes to red labeled on top of the ECM Blue to blue etc. Reconnect your battery and start truck. If you get any sort of hiccup strange Idle anything out of the ordinary turn the truck off and double check all connections. Here is a quick guide from GM about the procedure
Correction
Using harness jumper wire and instruction kit, P/N 12167310, revise the wiring harness at the VCM connector. Corrections were made to the VCM beginning 2/14/96. The corrected VCMs are identified with service number 16244210 on the VCM identification label.

Procedure
The following is a summary of the instructions included with the service kit:
1. Remove the negative terminal from the battery.
2. Move the wire located at connector J3 (WHITE/GREY/CLEAR), pin 18 to connector J1 (BLUE), pin 23.
3. Install the jumper wire between connector J2 (RED), pin 26 and connector J3 (WHITE/GREY/CLEAR), pin 18.
4. Install the tag included in the kit around the VCM wiring harness. This tag notes that the wiring harness has been modified.
5. Reconnect the negative battery terminal.

Road test to verify that the condition has been corrected. If any of the following conditions are noted, the transmission should be repaired or replaced using the most cost effective method. Canadian dealers should repair the transmission.
1. Transmission fluid oxidation or excessive sediment.
2. Transmission slip or flare after this service fix is performed.
3. DTC P1870 is stored on a 4L60-E (M30).

The following tools are available from Kent-Moore (1-800-345-2233) for use in removing and relocating the VCM wires:
1. J 41758 Terminal Tool; used to remove the wire from the VCM connector.
2. J 41759 Punch; used to punch a new hole through the connector seal

Source: https://chevroletforum.com/forum/silverado-fullsize-pick-ups-21/diy-walkthrough-vcm-ecu-ground-wire-update-39893/

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