Transmission Diagnostic Mode - issue I couldn't find here

[CallMeColt]

Everyone,

I spent a few hours searching here & read a few threads. I also have the WO troubleshooting guide .PDF & did find what covers part of the issue but still wanted to share as there's something odd.

Been looking at a M1097R1 that has a 4spd (4l80E?) in it. When you put power to it, the truck starts as it should. It was sitting for 8 months when I went to look at it & started in 3 cranks. Very clean & complete overall. The issue is the TRANS light is on when the power is moved to RUN & it stays there until the truck is off.

Tried to get it into diagnostic mode by jumping the pins (A & E if my memory serves me right, but I had the .PDF open in front of me at the time) & got nothing. I had forgotten to disconnect the glow plug controller/SmartStart box, & thinking that was it, turned everything off & disconnected it. With the SmartStart box disconnected, the truck is dead. No power, no crank, no lights, nothing. This is what has me stumped. I don't know much about the HMMWV yet, but if I'm not mistaken, the glow plugs just won't work with that disconnected, right? So I couldn't even attempt to get it in diagnostic mode with the box disconnected.

There is a section covering a TRANS light stuck on. I did on my own, look for the lead to the battery to be hooked up wrong, open breaker, etc. All seemed fine. There is a work through of testing pins on the TCM itself for voltages & whatnot that I did not do, but I will on my next check. The TCM box had been opened and someone was in there troubleshooting a bit at some point. All was very clean & in place. No obvious wire breaks or anything to be seen.

Is the dead truck with the SmartStart box disconnected a symptom of something like a bad ground, or something else? Again, my knowledge is limited but I do know the M1097R1 with the 4spd is uncommon so maybe there is something niche about this small batch of trucks or is it a retrofit? It is not previously owned by any civilians, it's from DLA this way.

If I can figure this out, I'm going to get the truck. It will be my COMMO truck that's going to get all my military radio equipment. I don't want it all to go in a 3sp truck. This one had COMMO in it previously so it's ready to go. Because this is my goal with it, I really don't want a truck project, just want to do basic fluids & checks, then start with mounting my antennas & comm systems.

As always, thank you in advance.

 

[m38inmaine]

Nice looking truck, I can understand you wanting the 4 speed but the good old TH400 has the advantage of no electronics to fail, once they do you are stuck with just 2nd gear if you are lucky. I am loading my M1097A1 with commo right now, it's only a two seat so I have limited space on the cab. The A1 trucks with a GEP 6.5 NA and 3 speed transmission to me is the best option as there are less things to fail. Good luck with the troubleshooting.

 

[CallMeColt]

Nice looking truck, I can understand you wanting the 4 speed but the good old TH400 has the advantage of no electronics to fail, once they do you are stuck with just 2nd gear if you are lucky. I am loading my M1097A1 with commo right now, it's only a two seat so I have limited space on the cab. The A1 trucks with a GEP 6.5 NA and 3 speed transmission to me is the best option as there are less things to fail. Good luck with the troubleshooting.

I'm in Texas where most roads & highways are 75mph. I have a 3spd & it will push 70mph, but it is way up there in RPM & will such diesel down running like that when I want to go for a rip. The 3spd is going to stay at the Roads End Ranch & want a 4spd for all the radio goodies. Once the truck is working, I'm not to worried about failures.

 

[Mogman]

Any time you disconnect the EESS box nothing will work, disconnecting the EESS was not mentioned in the trans supl. only the TSU
If you have a working trans light you should be able to go into the diag mode, if nothing else you will receive several number "12" codes, if not then you have ether a power issue to the TCM or a bad TCM

 

[CallMeColt]

Any time you disconnect the EESS box nothing will work, disconnecting the EESS was not mentioned in the trans supl. only the TSU
If you have a working trans light you should be able to go into the diag mode, if nothing else you will receive several number "12" codes, if not then you have ether a power issue to the TCM or a bad TCM

Okay, well maybe I was just being a dumb & didn't understand what it meant by glow plug controller. What does it mean by glow plug controller then?

 

[CallMeColt]

FYI just to add to this post, page 54 in the .PDF file covers the TRANS light staying ON STEADY and not going into Diagnostic Mode trouble tree.

 

[Mogman]

Okay, well maybe I was just being a dumb & didn't understand what it meant by glow plug controller. What does it mean by glow plug controller then?
View attachment 935725

That is the TSU, it is mounted in the right side of the water cross over on the front of the engine.

 

[CallMeColt]

That is the TSU, it is mounted in the right side of the water cross over on the front of the engine.

Well, there I go being dumb again. I'll need to unplug the CORRECT thing next visit to see if that makes a difference

 

[Mogman]

If you remove the harness from the TCM and the light still is on in the run position then there is a short in wire 657A to ground is basically what it is saying.

 

[Mogman]

Well, there I go being dumb again. I'll need to unplug the CORRECT thing next visit to see if that makes a difference

I am not sure why they are calling it the controller, in the civy world it was and is the glow plug controller, looks the same, uses the same round plug only in the civy world it very simply controls a relay connected to the glow plugs, I often wonder why nobody just reverts to that system although I would assume the controllers are few now that there are so few of the civy Detroits left on the road to support.

So not stupid you just did not ask the question.

 

[owensexport]

Your crank sensor is not working. The Trans controller will not turn off the light after starting unless it sees the crank signal from the front damper. Everything else will work perfectly and no codes will be stored

 

[Mogman]

Your crank sensor is not working. The Trans controller will not turn off the light after starting unless it sees the crank signal from the front damper. Everything else will work perfectly and no codes will be stored

That may be but he should still be able to put it in diag mode and get the diag code 12 even if no codes are stored.

 

[CallMeColt]

Your crank sensor is not working. The Trans controller will not turn off the light after starting unless it sees the crank signal from the front damper. Everything else will work perfectly and no codes will be stored

I thought this at first as well & is why I tried to pull a code. Not to say this isn't the issue, but it may by a symptom.

 

[CallMeColt]

After thinking about this for some time, I'm willing to guess what the issue is & I'm going to go back next week if I can to see.

So, like most surplus stuff, batteries are no good in there. A large jumper pack is being used. That said, its a 24v pack. This means, there is not a good 12v power source getting to the TCM. Even when the truck is started & driving around, the 12v side of the alternator isn't overcoming the dead/bad cells of the battery wired to the 12v side.

Could this have damaged the TCM? Yeah. They did this a bunch of times before I looked at the truck. What I'm going to do is bring my 24/12v jumper pack & put in in 12v mode on the batter used for the 12v side & see if it will then give correct power to the TCM, while the 24v is hooked to the slave port and see if it will respond to go into diagnostic mode.

Does this make sense & sound like a good idea to you with more experience than me? This will all be on top of what I shared above, going through the TRANS light staying on.

 

[owensexport]

Put 2 new batteries in the truck, don't try to operate off of jumper packs

 

[CallMeColt]

Put 2 new batteries in the truck, don't try to operate off of jumper packs

I'm not buying two batteries to test a truck I'm just thinking about getting. If I already owned it, good batteries would have been in it before doing anything as is generally the first thing I do with equipment.