Got my truck driving great after lots of troubleshooting. Turns out the coil, which I replaced already, was bad out of the box.

Latest issue...driving along, truck suddenly wouldn't shift out of 2nd gear and the voltmeter slowly dropped to zero. Took truck to shop, they tested and said the ECU is bad. So I order a replacement ECU from All Computer Resources, and the truck runs great for 2 days.
Then suddenly, the exact same thing happens again. Truck wouldn't shift out of 2nd gear and the voltmeter dropped to zero.

What would cause this? I can see the transmission circuit being to blame for stuck in 2nd gear, but the voltmeter dropping to 0?
Or is it just a bad ECU again

Both times, throwing following codes:
code 1765 Trans 12 Volt Supply Relay Ctrl Circuit
code 743 torque converter clutch solenoid
code 1682 charging voltage low



Literally everything under the hood is new. New motor with ~200 miles on it, all new sensors, cooling and heating system. Only thing I didn't replace is the transmission (46RE)

 

Get the alternator tested.

 

Thanks! I learned a lesson...never assume that new parts will work correctly. Turns out my alternator, which is only a few months old, was only cranking out 11.9v. Got it swapped under warranty today.

I should have learned this before when the coil I bought at Advance Auto was bad out of the box. Sad that quality control is so poor nowadays

 

Thanks for the update and glad that fixed it!

 

Well strike that....new alternator in, checked/cleaned connections and grounds, cleaned battery terminals, anything I could see is good to go. Fired it up, hooked up 2 multimeters to confirm...nope, still only seeing 11.9v at the battery. Raised RPMs, same thing. So much for crossing my fingers. Apparently the voltage is regulated by the ECU (or PCM, whatever its called)....but a spare ECU just arrived that will go in today. This will be my 4th ECU this year. Something isnt adding up.

 

4th PCM for the same reason?

 

I installed a replacement PCM this afternoon, that resolved the voltage problem. So it wasnt the alternator, but at least I know now. Voltage is back to normal. This PCM was bought from a salvage yard up north.
The previous 3 have all been replaced through All Computer Resources. The PCMs have been swapped for different issues; initial one was swapped for a misfire after warming up. The 2nd was swapped for no signal to automatic shutdown relay circuit. The 3rd was swapped for transmission stuck in 2nd gear. Each time I sent it in, they confirmed through their testing that the PCM was at fault and was covered under warranty.
I can't complain about their customer service, but the PCM they sent me each time only lasted anywhere from 9 months to 3 days. Odd.

 

Yeah, some of the 'remanufactured' PCMs have more problems than the one you are replacing. I see horror stories about almost every single one of them....... I don't know what their process is, but, obviously, it needs some revamping.