That’s what throws me off. The PCM is getting power and I’m even getting power to the CTM under the dash, which to my understanding is the communications bus. But the fuel gauge stays off until communication comes back.

I did a lot of wire checking and testing today, found 1 wire in the engine harness that shows open, unfortunately it goes throughout the truck all the way to the backup lights.

Found another circuit that had roughly 30 ohms of resistance where everything else was down around 1-2 ohms. That circuit passes through a relay and down to the transmission, so I’m thinking the added resistance came from the transmission solenoids, but I’m going to check those connections tomorrow.

I also tested all relays in the PDC and they all tested ok.

I also called a couple local dealerships and the service advisors both said similar things about the P1491 code. They said that more than likely the PCM is getting signals that it can’t find the correct code for, so it throws the only thing it thinks it correct. They both said it’s probably due to a wiring issue or bad ground. One did say that he’s seen these trucks throw a code for the brake light circuit directing you to the left or right brake light circuit and it was actually in the 3rd brake light, but the PCM doesn’t have a code for that so it uses either the left or right side instead.

 

I don't think the PCM cares about light bulbs in second gens. It has no way of knowing if they are working or not. It doesn't monitor them.....

Backfeeding from other circuit confusing the PCM though, that sounds perfectly reasonable.... Just, which circuit...... That's gonna be the fun part.

 

A solution have been found! After spending the better part of 2 weeks going through the truck with a fine tooth comb, I found a few issues that needed to be addressed but were not the source or the problems. I ended up replacing the ignition switch and lock cylinder, crankshaft position sensor, Central Timer Module (CTM) positive battery cable, and plugs that go into the PCM. After all that, and replacing the heater core and AC evaporator, I took it out for a test drive. First time out went great, no issues, drove nearly 30 miles. Then today I went out and made it 6 miles before I got hit with hesitation, and shut down followed by a "no bus". I waited about 10 minutes and it fired back up, got me home with no issues. I called the company I bought the PCM from, Car Computer Exchange and spoke with their tech support. After telling them what all has been happening and giving them the list of codes I was piling up, they said it definitely sounds like a bad PCM, probably corrupt software. So I have to send it back to them, but they give you 2 replacements under their lifetime warranty, so it's not all bad.

 

They have one of the worst reputations for shipping broken stuff...... Of course, I am not aware of ANY PCM companies that have good rep....