This evening my son reported that the truck wouldn't start, and when I went to investigate I found that I could start and drive the truck normally with the transmission in Neutral but not in Park. No codes or other symptoms like flashing M & S lights, just darkness when the key is turned with the trans in Park.

I first thought it was a problem with the XYZ switch. (Which I replaced eight years and 70,000 miles ago. The "new" one is now older than the original was when it failed.) But I double checked and the PRND321 lights light up correctly on the selector indicator on the console and on the instrument panel. That tells me the ECU is getting the correct signals, I think, but yet the starter inhibitor (i.e. XYZ) is not allowing the starter to engage in Park.

I now think it may be a matter of a minor adjustment to the XYZ switch, per RAVE, or of the selector cable, but I thought I'd ask the opinion of others here in case I'm overlooking something. Thanks.

 

I think you hit the nail on the head,

 

Day 2. Today I got another call from my son telling me the truck wouldn't start in Park or in Neutral. I went to where he was parked and tried adjusting the switch but had no luck. Eventually I had the truck towed to my house.

I'll try again to adjust it, but I still wonder why it won't allow the starter to run if PRND321 is displaying correctly. If the computer is convinced the trans is in Park to display P on the instrument panel and to illuminate the light on the shifter why is that not enough to let the truck be started?

Any other constructive suggestions will be appreciated.

 

Well, I've adjusted the XYZ switch through its full rotational range, with my son trying to start the engine at various settings. No luck. And the PRND321 indicators stayed on through the full range.

 

This isn't going well. I was removing the XYZ to bench test it. After I loosened the nut that holds the selector lever on the selector shaft the nut simply spun in place, clearly stripped, and I could neither remove it or re-tighten it. I tried cutting it off with my nut splitter but couldn't get enough leverage lying on my back. Stay tuned for more news about that.

In the meantime I'm pretty well convinced the problem isn't with the XYZ. After reviewing the RAVE again it seems clear that if the computer is displaying PRND321 correctly its getting the signal it needs to activate the starter so it must be something downstream. I guess I'll dive in and start testing other circuits, etc.

Still looking for ideas.

 

I finally got the XYZ switch off the truck and will rebuild it, but the transmission selector shaft is in bad shape (see pic). I must have done the damage eight years ago when I changed the XYZ the first time. Looks like I'll need to file down the shaft and then use a 7mm die to try to cut new threads. Ugh. If that doesn't work I guess I'll need to drop the pan and the valve body and replace the shaft. I looked for the shaft in Microcat but didn't find it listed. Does anyone have a part number for it?

 

Another update. First, I was able to repair the old trans selector shaft by filing it down and then cutting new threads. It's now threaded 5/16 although the thread height is pretty shallow so I'll need to be careful to not overtighten the nut and strip the threads again.

I also took apart the XYZ switch to see what might be wrong with it. The interior design was completely different than what's shown in other threads about rebuilding the XYZ, plus it wasn't marked ZF and its cover was black plastic and not the tan seen commonly.

I found what I thought was the problem; a tiny copper contact that was somehow bent out of shape and wasn't closing the circuit when in Park or Neutral. I tried to bend it back into position but it broke off. I was then able to cut and fit a small strip from an aluminum can that I hoped would work until I could get a replacement XYZ. The PRND321 indicators all lighted correctly and the truck started immediately after I reinstalled the switch. Unfortunately it started only once, so I removed and took apart the switch again and made a slight adjustment to my repair. Put it back in and the truck again started right up, but again started only once.

I'm ordering a replacement XYZ today but won't be able to install it until next week. I hope this solves the problem.

(Note: I did also remove the brown lead from the starter solenoid and tested whether or not it was getting voltage when the key was turned to Pos III. Nothing. That's what pushed me back to the XYZ even though all the PRND321 indicators were working properly.)

 

Did it look like this inside?

 

No, it looks like this. The second picture is of the rotor turned upside down. The eight contacts (seven in the pic; one was broken off already here) rotate against the tracks on the body of the switch, opening and closing circuits depending on whether they're touching metal or plastic.

 

Looks like it was the XYZ. I ordered a replacement from one of our well known forum vendors and all seems well now. Seems that the contact in the switch that tells the BCU it's in Park or Neutral must be different than the one that tells the tranny ECU PRND321 since those instrument panel indicators and shifter surround lights always worked fine.

That's the opposite of what happened eight years ago when it would start just fine but because the tranny ECU couldn't see where the shifter was positioned I couldn't remove the key. That happened the first evening of a week-long trip to Boston and the Cape. Luckily it was a vanilla key in the ignition and not the keyless entry fob. The key stayed in the ignition switch for the entire trip and we locked and unlocked the truck with the fob.