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Discussion Starter · #1 ·
Engine is a 4.2/4200 Vortec...

I bought this Trailblazer about 3 months ago, and the seller told me the transmission was rebuilt and showed me the receipts. I don't drive and bought this for my wife and don't remember if I test drove it honestly or how I got it home lol...

But it drove fine for about a week or two, then started stalling, then acting like it wasn't shifting into 2nd and 3rd gear and ran really rough, and finally just stopped shifting into gear.

I had the shift solenoids replaced... nothing.

I had the transmission replaced... nothing.

Tested the round connector on the passenger side of the transmission, with the key in the on position, and while it was running and shifting with the shifter... no voltage from the 12v pin.
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Starting to think this is a security system or electrical system issue causing this problem. Posted about this in a Trailblazer Facebook group and received one answer lol he said to check the ECM/TCM.

But the ECM/TCM I'm assuming he is referring to is what is also called the PCM ? All I can find is this piece here with a Black, a Grey, and a Blue connectors bolted it...
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Do any of these connectors have anything to do with the TCM or providing power to the transmission ? If not, where can I find the TCM and how do I test it ?

I know the security system causes the engine and fuel injection system to disable, but does it also disable the transmission in any way ?

Just really need to figure out what is causing this problem...

Thanks in advance guys !
 

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Engine is a 4.2/4200 Vortec...

I bought this Trailblazer about 3 months ago, and the seller told me the transmission was rebuilt and showed me the receipts. I don't drive and bought this for my wife and don't remember if I test drove it honestly or how I got it home lol...

But it drove fine for about a week or two, then started stalling, then acting like it wasn't shifting into 2nd and 3rd gear and ran really rough, and finally just stopped shifting into gear.

I had the shift solenoids replaced... nothing.

I had the transmission replaced... nothing.

Tested the round connector on the passenger side of the transmission, with the key in the on position, and while it was running and shifting with the shifter... no voltage from the 12v pin. View attachment 57854 View attachment 57855

Starting to think this is a security system or electrical system issue causing this problem. Posted about this in a Trailblazer Facebook group and received one answer lol he said to check the ECM/TCM.

But the ECM/TCM I'm assuming he is referring to is what is also called the PCM ? All I can find is this piece here with a Black, a Grey, and a Blue connectors bolted it... View attachment 57856 View attachment 57857

Do any of these connectors have anything to do with the TCM or providing power to the transmission ? If not, where can I find the TCM and how do I test it ?

I know the security system causes the engine and fuel injection system to disable, but does it also disable the transmission in any way ?

Just really need to figure out what is causing this problem...

Thanks in advance guys !
Stalling - remove the throttle body and completely clean it with intake cleaner. Check your vacuum lines, especially the one that goes to the intake manifold , sometimes it cracks near the clamp. Transmission -Did you replace all of the shift solenoids? Or just the A and B one's? Did you also replace the pressure switch manifold ? Sometimes the pressure switch manifold gets loaded up with fine metal particles, they get shorted out and the transmission doesn't shift properly ($25) part.
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Discussion Starter · #3 ·
I didn't realize there were more shift solenoids besides A and B, I only replaced A and B solenoids.

I suspected the pressure switch manifold, because the round connector I tested for voltage runs straight from the pressure switch manifold, but never checked it out because I thought it was the neutral safety switch...
 
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