Okay so a couple weeks ago I changed my heater core in my 2002 Blazer 4wd. Since then I have issues where most of the time the only gauges that work are the voltage and oil pressure gauge. Then the key will not return to the home posistion or release the key without pushing the button under the column. And then finally the transmission if put in drive starts and stays in 3rd. I can manually shift 2nd and then 3rd but no OD or 1st gear. The codes that the money light tells me are P1860 and all the other shift solenoid and torque converter electrical ckt codes. I have replaced the ignition switch with no change. I am honestly reaching the end of my rope with this and I’m ready to burn it.

 

I've heard stories of how difficult changing the heater core can be with all of the wiring connections to get right during the reassembly process. Could it be one of them? The biggies I would think would be the ones to the Body Control Module (BCM) right above the transmission hump and the Body Relay Block (BRB), above the parking brake foot lever.

 

 

Well today I pulled the dash forward. I dropped the column and disconnected two of the three wiring harnesses. Once I reconnected them and reconnected the battery with the column and dash still unbolted. The key released when I turned the ignition off. Then I put the scanner on and cleared the codes and the light shut off right away. Everything is working fine after reassembly and I'm gong to say this was a lose/pinched wire.

 

Congrats on finding an easy, if not time-consuming, fix. Also thanks for posting a follow-up. I make a point of thanking anyone for doing so as it is the final resolution of our problems where we get the most important information from which others can learn!