I've found lots of useful info on this form in the past, and some ways to troubleshoot my current problem, but no solutions yet, so this is my first time posting on my own.
I have a 99 Dakota 5.2 4x4 automatic with about 140k miles.
The current issue is that, when it warms up, it will shut down. It started with some single shut-downs when driving (kinda scary, no abs or power steering at highway speed!). Now it's been sitting for a couple weeks and every morning it will start right up, run about 20 min, then shut down. By 'shut down' I mean no gas and no spark. When I turn the key I don't hear the fuel pump prime, and when I crank the engine I don't get spark (tested with spark plug test light).
If it sits a few minutes it will cool enough to start again, run for a while, then shut down again. Sometimes I get the 'no bus' on the odometer, sometimes I get a check engine light and I have a code reader that has yielded various error codes which I'll list below. Code reader can also read coolant temp and shut-down happens about at coolant temp of 170F. My current thinking is that my PCM is fried, and when warm it's shorting somewhere and triggering the ASD relay and throwing random codes. My hesitations in just replacing the PCM are:
1. Cost of new PCM
2. Bad PCM was caused by something else- and new PCM would get fried by same problem
3. Maybe I'm just an idiot and it's not actually the PCM and I hate to blow hundreds of dollars
Error codes I've received:
P1492 ambient temp sensor high
P0123 throttle position sensor A high input
P0505 Idle air control
P0443 evaporative emission system purge control circuit
P0108 MAP sensor
P1765 transmission power relay circuit
P0743 torque converter clutch solenoid
P0753 shift solenoid
All of these codes come and go like the wind. When I let the truck sit for a wile, when I come back and turn the key, I hear the fuel pump prime and it starts up and I don't get any codes.
I've read a ton of posts about what might be wrong:
PCM shutting down 5V to sensors- this isn't true for me. When it won't start I'm still getting voltage to the sensors
Crankshaft position sensor- Tested and seems to be fine, no change in voltage behavior between cold and warm shut-down. 5V supply, ground and signal all seem fine.
Bad fuel pump- it's not just the fuel pump, when there's no pump there's no spark, both come back together
Bad TPS- even when shut down 5V supply, ground and signal seem fine. Tested with voltmeter for voltage change on signal and resistance
Bad MAP- tested voltage and seems fine, and code reader has reading from this sensor
Bad ASD relay- I have a few spares and switching the ASD relay with another when shut-down happens doesn't get it going again. The fuel pump relay gets hot, but the ASD relay only gets a bit warm.
Bad ground wire or other wire short- I've disconnected the PCM plugs when shut down happens, and the PCM is still getting 12V from pin A2 and A17, and A31 and 32 have good ground. I've checked around for loose ground wires and haven't found any, but can't be certain I've found them all.
Bad Idle Air Control Valve- possibility- the sensor itself seems to work, though. It has 4 wires with 2@ 12V when cold and 2 grounds (key on). When warm and shut down, sometimes I can hear an electrical clicking sound coming from it and voltage is 12V, 2.5ish V, 0.4ish V and ground across the 4 wires. Not sure exactly how this sensor works electrically and what voltages should be while in operation. Mechanically I can see it move when not shut down and turn the key. My theory is that the wiring is going crazy bc of bad PCM and not the other way around (bad IAC causing PCM shutdown)
I did try the 'freeze your PCM' check (https://www.youtube.com/watch?v=Ea9jhBOEhT0) and it did seem to keep the truck running longer, but it's hard to tell because the truck is also cooling down when the PCM is in the freezer. Coolant temp at frozen-PCM shut down was about 180F. When shut-down happens, the PCM is not hot itself, and as I said above, seems to be still supplying signals normally (except to the Idle Air Control sometimes). The only consistent behavior when shut-down happens is the no-gas/no-spark. All the other error codes come and go.

So, if you've made it this far through my description, then THANK YOU! You must either also be in a bad spot or love these trucks as much as I do. This thing has been a tank and seen a lot of abuse but has kept on chugging and been relatively easy to fix when things go wrong, until this time...
Any advice would be appreciated. I'm trying to think of additional things to check besides just replacing the PCM or taking it to the dealership and getting a diagnosis, because that will probably cost about as much as what the truck is worth at this point...

 

So go the other direction. Start with the truck stone cold, start it up, let it idle, and point a heat gun, or even a hair dryer at the PCM, to warm it up faster. See what happens.

 

Wow. So simple.
Was away for a chunk of the day, so truck was nice and cool when I came home and read HeyYou's post. Truck started right up. Turned it off quick, set the PCM in the sun for an hour, put it back in- no fuel prime, no spark, 'no bus' on odometer.
Put it back in the freezer for an hour- started right up.
Ordering a new PCM next, but wanted to say THANK YOU!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! before I did anything else.
I'll post again when I get the new part in and have the results to share.

 

Awesome. Let's hope that's the end of it.

 

Forgot to close the loop on this thread. Got the new PCM, installed it, and that seemed to do the trick!