12200411 PCM swap for 1996 to 2000 GMT400 trucks

Spareparts · Oct 3, 2022

Ah well i guess i have a couple more wires to run.
I made a appointment with Black Bear next week as i have a couple more little problems that need adjusting.
The truck now starts and dies the first try then it will start and run. Also, it has to spin for a few seconds before it will start. Before the swap it started immediately.
When up to temp it would idle very smooth. After swap, it's slightly rough now when up to temp.
What wires do you tap into at the PRNDL switch?

BeXtreme · Oct 4, 2022

Spareparts said:
Ah well i guess i have a couple more wires to run.
I made a appointment with Black Bear next week as i have a couple more little problems that need adjusting.
The truck now starts and dies the first try then it will start and run. Also, it has to spin for a few seconds before it will start. Before the swap it started immediately.
When up to temp it would idle very smooth. After swap, it's slightly rough now when up to temp.
What wires do you tap into at the PRNDL switch?

It should be in the spreadsheet you got from lextech. It says optional, but really shouldn't be. Getting the CASE learn done might help with the first start issue.

1998_K1500_Sub · Oct 5, 2022

BeXtreme said:
Did you have the pins grounded per what I said in post #758? The 0411 needs to know you have it in park or neutral in order to run the CASE relearn

BeXtreme said:
You have to tap into those signals at the cluster or trans in order for the ECU to get that signal. OR you need to ground those two wires so that it thinks it is in Neutral or Reverse and allows the CASE relearn to happen.

BeXtreme said:
It should be in the spreadsheet you got from lextech. It says optional, but really shouldn't be.

In the spreadsheet I got from Lextech for my 1998, no mention is made of these connections.

Was it an oversight? Or, does this not apply to 1998?

(edit) See the responses which follow in this thread.

The only mention in the spreadsheet about relearn, which I received from Lextech just last week, is:

"You will probably need to do a Crank Relearn after the PCM swap. If so, there will be a check engine light with code P1336 until you perform the relearn. Even if you don't get a P1336 code you should still perform a Crank Relearn."

BeXtreme · Oct 5, 2022

1998_K1500_Sub said:
In the spreadsheet I got from Lextech for my 1998, no mention is made of these connections.

Was it an oversight? Or, does this not apply to 1998?

I suspect it was an oversight.

The only mention in the spreadsheet about relearn, which I received from Lextech just last week, is:

"You will probably need to do a Crank Relearn after the PCM swap. If so, there will be a check engine light with code P1336 until you perform the relearn. Even if you don't get a P1336 code you should still perform a Crank Relearn."

My spreadsheet has a bit at the very top of the first page that says not all tuning software can turn off the PRNDL switch and if you need it(most do), that you should tie into the 4 wires either at the switch or behind the cluster. They are C1-32: Black/white, C1-34: White, C1-72: Yellow, C2-62: Gray. That's on a 97... but I would imagine its the same on your 98.

yevgenievich · Oct 5, 2022

For 98 and up park/neutral wiring is already at the ecm

Spareparts · Oct 5, 2022

It was my understanding if your pre-1998 PRNDL did not work then you needed to add wires. 1998 and later did not need any added wires and all things work as intended.
I will tap into the two wires and let Black Bear tell me to ground them or not when im there Tuesday. I did step up to the in person tune.

Spareparts · Oct 10, 2022

Appointment was changed to Friday

It was 40 outside this morning and it was very hard to start.
I'm pretty sure the water temp sensor on the front of the block is good, I think. It's almost new maybe 4 months old. The dash gauge and Torque both read close to the same.

Spareparts · Oct 10, 2022

I really suspect it's the tune as it seemed to start/run fine before the swap. but could a bad IAT cause this hard start when cold?

L31MaxExpress · Oct 11, 2022

Did you fix the EGR wiring? The 0411 controls the EGR valve in a different manner and a new 12V supply wire has to be run back to the PCM from the valve to the corresponding pin on the PCM. If not the valve will hang fully open. Easy way to check to see if it is the problem is to merely unplug the valve.

Spareparts · Oct 11, 2022

I'll try that as I never read that anyplace else.
I would have thought that it hanging open it would run like cr*p all the time though?

12200411 PCM swap for 1996 to 2000 GMT400 trucks

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