05 lly 235K miles, all stock.
Started with leaking trans selector seal. Removed NSBU switch replaced seal. 1-2 weekly later started getting selector inhibitor messages on the dash with no gear selection indicator on dash. If you turned it off and started back up it would go away and go into gear.
thinking the old NSBU switch was bad and oil soaked I replaced it (nsbu is single plug). Issues continued over the coarse of 12 months and started coming more frequent. Then back in Oct it would take multiple key cycles for it to work again. Check plug and nsbu switch for connection. Visually things looked fine. Then it progressed to check engine light.
Codes P0700, P0872, P842...Cheap code scanner would clear codes, then it would go into gear and work fine. As time went on it took longer to clear code so it could be driven. It was also intermittent. You may or may not need to clear codes at each restart when making multiple short trips. BTW once the codes had been rest you could hear and sometimes feel a shift valve reset.
If I disconnected the batteries and reconnect there were no issues for multiple start ups.
Issue continued to progress and frustrating so I dug into the valve body and put all new shift valves in (valves slide in and out smoothly). Tested all shift solenoids. Replaced pressure switch and internal wiring harness. Found not debris in pan that appeared to be from a mechanical issue.
Did driven relearn for trans. Issue still returned.
Went thru TCM connectors and none appeared to have issues.
Put two new batteries after getting low voltage code and batteries being 10 yrs old.
Gave truck to a GM tech to re-flash TCM. He could not communicate with it. Got reman TCM and he still could not communicate with it.
At this point he still could read DTC's. Once the second TCM did not have communication he checked ECM wiring. I'm told it all checked out including under the fuse box under the hood. He say he did a hard ECM reset also (not sure what that is).
After all that there is zero communication to ECM, TCM, BCM.....DLC has power and ground. I was also told he checked the com wires as well.
Now the truck is stuck in second gear, check engine light on, abs & brake lights are on, service brake system flashes, no gear indicator and no working speedo.
Once I got it home I looked at fuses and found ECM2 blown. Replaced it and nothing changed. Unhooked the batteries, waited, reconnected. Same dash issues, scanner continually trying to read.
I have a copy of the TCM pin out info for testing wires but cannot find the ECM.
Can't afford to send it to a $200 per hour dealership to check harnesses. I'm not a good diag guy but can take solid direction and guidance well. Some lingo and acronyms I'm familiar with but would need it dumbed down intentionally.
I would really appreciate the help.
Started with leaking trans selector seal. Removed NSBU switch replaced seal. 1-2 weekly later started getting selector inhibitor messages on the dash with no gear selection indicator on dash. If you turned it off and started back up it would go away and go into gear.
thinking the old NSBU switch was bad and oil soaked I replaced it (nsbu is single plug). Issues continued over the coarse of 12 months and started coming more frequent. Then back in Oct it would take multiple key cycles for it to work again. Check plug and nsbu switch for connection. Visually things looked fine. Then it progressed to check engine light.
Codes P0700, P0872, P842...Cheap code scanner would clear codes, then it would go into gear and work fine. As time went on it took longer to clear code so it could be driven. It was also intermittent. You may or may not need to clear codes at each restart when making multiple short trips. BTW once the codes had been rest you could hear and sometimes feel a shift valve reset.
If I disconnected the batteries and reconnect there were no issues for multiple start ups.
Issue continued to progress and frustrating so I dug into the valve body and put all new shift valves in (valves slide in and out smoothly). Tested all shift solenoids. Replaced pressure switch and internal wiring harness. Found not debris in pan that appeared to be from a mechanical issue.
Did driven relearn for trans. Issue still returned.
Went thru TCM connectors and none appeared to have issues.
Put two new batteries after getting low voltage code and batteries being 10 yrs old.
Gave truck to a GM tech to re-flash TCM. He could not communicate with it. Got reman TCM and he still could not communicate with it.
At this point he still could read DTC's. Once the second TCM did not have communication he checked ECM wiring. I'm told it all checked out including under the fuse box under the hood. He say he did a hard ECM reset also (not sure what that is).
After all that there is zero communication to ECM, TCM, BCM.....DLC has power and ground. I was also told he checked the com wires as well.
Now the truck is stuck in second gear, check engine light on, abs & brake lights are on, service brake system flashes, no gear indicator and no working speedo.
Once I got it home I looked at fuses and found ECM2 blown. Replaced it and nothing changed. Unhooked the batteries, waited, reconnected. Same dash issues, scanner continually trying to read.
I have a copy of the TCM pin out info for testing wires but cannot find the ECM.
Can't afford to send it to a $200 per hour dealership to check harnesses. I'm not a good diag guy but can take solid direction and guidance well. Some lingo and acronyms I'm familiar with but would need it dumbed down intentionally.
I would really appreciate the help.
