so, I got my hands on a wiring diagram for this vehicle, and looking it over with a microscope, I can only see 2 sensors on 5v ref circuit....throttle body position sensor and accelerator pedal sensor. Other component receiving 5v power from pcm are crankshaft position sensor and oil pressure sensor. Neither of those has 5v ref. Not an electrician but it seems to me that the red lightning bolt with limp can only be due to either faulty sensor at throttle body (though it is a new aftermarket unit) or the pedal sensor (also replaced)...or the wiring to these 2 components or connections.....
Please tell me what I'm missing.

The vehicle starts and idles from cold as if nothing wrong but after getting warm, it throws cel and codes 0642 and misc others and lightning bolt and limp.

 

Here is the flow chart for the 0642

 

Thank you!!! this is one of the most helpful replies I've ever received on any forum. I wish you weren't on the other side of the country, I would just hire you to fix my van. I am beginning to lean to crankshaft position sensor, because I remember seeing on other threads that people fixed the 0642 by replacing that sensor.
I have avoided taking this van to a shop because I just don't have faith that the hourly labor cost of detective work would not amount to an unaffordable price for me as a senior on fixed income. So...I have gone down the diy parts changing rabbit hole but even still I have spent less than 2 or 3 hours of hunting for problem at a shop and no guarantee they would solve it. So,,,I continue. But, I have a question on the crankshaft sensor....would I not get a related fault code for crankshaft sensor if it was misbehaving?
I did buy a reprogrammed pcm from Flagship One that supposedly did not need anything but plug and play, but when I put it in and started van, at first it immediately threw cel and a bunch of codes. I double checked it and it looked like I did not have harness plugs seated fully so I managed to get them more firmly seated and the faults went away but there was zero throttle response. I don't have a relearn scanner. Since it was supposed to be plug and play, I complained to Flagship One and reinstalled the old pcm. Now I have throttle response again, but back to square one on 0642 and limp.
FYI, whatever this problem is, it has deteriorated in last few weeks. I used to be able to clear codes and drive the van around town a bit before it limped again, but now....it is throwing cel and limp within a few minutes of idling on driveway. I'm unable to drive the van around the block at this point. So...I ask...which component would deteriorate without being driven?...I wouldnt think a chafed wire or connection would worsen with the van sitting still on the driveway.??

 

buy a good scanner so you can do things like a throttle relearn look on amazon for kingbollen or launch scanner. most can do whats needed for a simple DIY

 

yes I need to do that and subscribe to your youtube channel too. FYI, I was just doing more poking around and may have found my shorting issue. There is a 3-loom pigtail looking bunch or wires at the rear side (firewall) of engine above transmission that are wrapped in a foil looking insulation material and with engine idling and no cel , I jiggled that pigtail and there was a short and immediate engine stall with cel and the lightning bolt. It's really hard to see back there as to where they go but I can see 2 harness connectors back there and the 3rd one disappears into ?. I examined as well as I could with flashlight and mirror but I can not see chafing or exposed wire, but it definitely shorted out when I jiggled that pigtail and i assume it is contacting the block. So I rigged up a strap to lift and hold that 3 bundle pigtail up and away from the block and started engine. I still have the saved, inactive faults but no cel or new ones. I am done for the day and will let engine cool overnite and tomorrow maybe see if my lifted pigtail is still providing the fix. I don't know what those sensors are back there (top of engine at the back). How I get in there to strip away insulation and look for the bare wire I'm not sure. A bandaid to prove my diagnosis would be to more permanently strap up that pigtail and drive it. See what happens.

 

follow up on this.....I did eventually find a ground short from an apparent chafed wire that was shorting to the block above bank one and under the throttle body. It is a pigtail wire harness with either 3 or 4 wires coming out of it and I believe 2 of the sensors they lead to are oil pressure sensor (on 5v supply) and knock sensor. Due to the inaccessibility to actually get eyes on the chafed wire to repair, I have suspended the wire pigtail up off the block with multiple zipties.....and scanner is now reading zero faults. I'm hoping this is the end of my saga and I will resume driving the van. I will monitor the zipties daily and eventually carve out the time to do coils and plugs since that requires removing the upper intake plenum and at that time I will see if I can more permanently repair the chafed wire.

 

good deal wire issues are always fun to try and find .