Great infor Guys. Chet

 

Now that is enlightening. You are the answer man Roland.

I would never have thought PTO or non-PTO. If asked I would most likely come up with the right answer. If not asked I could possibly come home with the wrong part. Actually I doubt I would because I would go to the parts counter with old part in hand like I usually do.

 

Great post! Helped me out with my problem.

 

What should the readings be using a multimeter to see if the alternator is faulty?
thank you.

 

You can't diagnose a failed rectifier diode with a multimeter. You need an oscilloscope.

 

I have too. Twice. On the same truck.

It has two alternators, and the failure of each (at separate times) affected the transmission, to the point of setting codes and blinking the OD light on the column shift handle.

The diagnostic trouble code identified the TSS sensor data being bad each time.

The bad data manifests itself physically, with delayed engagement, hard shifts, highly elevated idle, and ultimately, an inability to drive the truck.

A new alternator fixed the problem each time. The sensors are still all original on the transmission. I never tested or even touched them.

 

@Y2KW57
So were there some other symptoms? What caused you to go after the alternator and not troubleshoot the seemingly obvious tranny issues?

 

The LIFO principle.

Last In, First Out.

My lower alternator pulley broke, and jacked up the drive bearing and rotor shaft of the lower alternator. Never figured out why that happened, but I had to drive home with no drive belt at all. Meaning no engine fan, no power brakes, no power steering. Made it though.

Since this event took me by surprise, I couldn't apply my scorched earth evaluation of replacement alternators before I needed the truck, so I looked on craigslist for a 6G alternator, found one that was less than $20, and another for $10, and figured that between three alternators, I could mix and match parts (bearings, drive ends, slip ring ends, rotors, stators, voltage regulators, and diode bridges) to make a working alternator, to tide me over until I found something in the more "ultimate" class of alternator that I'd be satisfied with.

I built the alternator, took it to an alternator repair shop for testing, it tested good, so I installed it in the truck.

Not long after that, the engine would ramp up to 1,500 rpm, there would be delay in shifting to drive, and the 1-2 shift was an abrupt SLAM. Then the overdrive light started blinking. All the symptoms were transmission related. There were no electrical issues or symptoms manifest (ie, no difficulty starting, no battery light, no dimming headlights, etc).

At first I thought it was a streak of bad luck... when it rains it pours... if it isn't one thing it's another... Murphy's Law. I was thinking the trans was toast, and now had to scrape together four figures for a 4R100 R&R. But since the overdrive light flashed, I knew that a code was set in memory, so I hooked up an NGS scan tool to see what diagnostic codes were set. It was the TSS.

The TSS, OSS, and CMP are all Hall Effect sensors. They are non contact sensors, relying instead on changes in magnetic fields... which can be distorted by stray AC manifesting as electro magnetic interference.

This is why a lot of folks over the last 20 years report camshaft position sensor failures only when it rains... and only in light rain, not in heavy rains. It was deduced that in light rain, they are using their windshield wipers in the INTERMITTANT setting, and the manner in which the wiper motor is controlled in intermittency produces electrical noise that is transmitted through the wiper motor ground that is shared with the PCM on the firewall. For years, the trick was commonly known to just keep the wipers in steady state slow or fast speeds, and avoid the intermittent settings. Some folks even experimented adding noise chokes on the wiper motor wiring. Anyway, we know that Hall Effect sensors are sensitive to electrical noise.

The lower alternator is mounted to a bracket under the passenger side of the engine, and that bracket simultaneously serves to mount the sub-bracket that supports the hard transmission cooling lines. It wasn't so much that I was thinking of these tubular metal lines serving as antennas or conductors of electrical noise generated at the alternator I rebuilt from craigslist parts... it was the fact that the last thing touched on the truck prior to the transmission showing signs of failure was that alternator. LIFO.

So I reached through the wheel well and disconnected that lower alternator. INSTANTANEOUSLY, the transmission problems went entirely away. So I left the lower alternator in place, unplugged, and happily used the truck, for months.

Then one day, many months later, the transmission suddenly started failing again, in the same way. I checked to make sure that the lower alternator was still unplugged, and it was. I still hadn't gotten around to replacing that alternator yet because I didn't need to ... I still had the primary alternator up on top of the engine that was working just fine alone, like most people's single alternator trucks. Or was it? I popped the hood, and put my hand on the top alternator. OUCH! Way too hot to touch. Never felt it that hot in all the years I had the truck, which was perhaps 14 years by that time. It became immediately apparent that my top alternator, when working by itself, was taxed to the point of accelerated internal component failure (likely a diode issue).

At that point, I realized that the only reason why my truck didn't eat a steady diet of alternators, was that it had two alternators that were sharing the load. Once the lower alternator was unplugged due to it's excess stray electrical noise effecting the transmission, the upper alternator was left to work alone, and it already being 14-15 years in service, soon failed.

Once I replaced the top alternator, the transmission worked just fine again, as if nothing ever happened. This time I replaced the upper and lower alternators, so that I could have both plugged in and sharing the load again.

So what caused me to go after the alternator instead of the transmission? In the first instance, it was the LIFO principle. In the second instance, it was previous personal experience.

 

Excellent explanation and a good lesson for us all. Thanks for sharing

 

@Mark Kovalsky, does the alternator have to be out of the truck and bench tested for this condition, or can it be done while still in the truck?


@Y2KW57, excellent information, as always! Very helpful details, and the context is just outstanding.

 

It is much easier to diagnose while in the truck.

 

Thanks, Mark.

 

Do i need a different pcm to run a pto transmission? My pcm has pin 66 which is pto enable.??

 

There is no special PCM for a PTO transmission.

 

Thanks Mark. Did you work on engineering the 4r100?