32RH P0740 Code

[Ken G Ford]

Hi everyone, hoping some one can give me some ideas.

Some background Info. Engine and Transmission both professionally rebuilt.
In the process of fixing a leaky rear main seal under warranty, the mechanic damaged my PCM.
probably with a Battery Charger. They installed a new ECM and after getting my TJ back , it is now throwing a P0740 Code.
I noticed that the transmission TQ Lock out is not locking out. i.e. RPM never drops once in third gear.
Its suppose to drop 400 or 500 RPM once up to speed which it never does.
Took it back to Transmision shop since it is also under warranty and initially they said it was just an adjustment.
when I test drove it the shifting seemed smoother 1st thru 3rd gear but again the TC never locked up. After 3 miles f test driving it the
Check Engine light is on with the P0740 Code so I left it with the transmission shop to trouble shoot again.

My question is this:

Does the PCM tell the transmission to lock up? or does it simply lock up due to transmission pressure?
Either way the TC is not locking up as it never drops 400 to 500 RPM in 3rd and above 45MPH.

I have personally checked the wiring going to the transmission and all appears clean and undamaged and even reseated the ECM

Just trying to Trouble Shoot to see if its the TC Lock Out Solenoid in the transmission or if its the replacement ECM?

Trying to figure out if the engine mechanic inadvertently thru in a Manual PCM instead of the automatic and left him a message to try and find out which company he purchased the ECM from. Figured the company who supplied the re-manufactured ECM should be able to tell me.

Again, just trying to trouble shoot to know if its Transmission issue or re-manufactured ECM Issue.

 

[hear]

The computer tells it to lock up. First easy check is to validate you’ve got connectivity & no shorts on the 2 wires from the TCC plug back to the PCM (I can’t pull up the wiring diagram to see which pins on the PCM). I think there is also a fuse on that circuit but I can’t say for certain. Assuming your wiring passes that test, then it’s probably a bad solenoid.

Theoretically you could rig up a manual switch to engage the TC lockup, but you’d want to be sure to remember to unlock it!!

Alternatively I suppose you could measure for either voltage or ground on those wires while the jeep is running and in a scenario where the TCC would lock up. Lots of hot spinning stuff in that area so I’d be real careful doing anything like that.

 

[hear]

Although the lockup is closer to like 150 rpm drop, not 400-500 as you mentioned.

 

[Jerry Bransford]

Although the lockup is closer to like 150 rpm drop, not 400-500 as you mentioned.

X2.

 

[Rickyd]

Although the lockup is closer to like 150 rpm drop, not 400-500 as you mentioned.

The transmission needs to be up to temp as well if i remember right? My last tj would only lockup after driving it a while.

 

[Jerry Bransford]

The transmission needs to be up to temp as well if i remember right? My last tj would only lockup after driving it a while.

It shouldn't have needed to be warmed up for the 32RH to lock up.

 

[macleanflood]

Finding out where the shop sourced the ECM will tell you something.

Wondering if you shouldn't send it to @Wranglerfix for testing.

Do you still have the original? Might be able to get it repaired.

-Mac

 

[Ken G Ford]

Thanks everyone for your thoughts. So at least I know the signal to lock up TC comes from ECM.
The TJ is currently at the transmission shop waiting to be looked at again on Monday.
Before taking it there, the wiring looked great and although I personally did not do a continuity check with a meter on each of the two wires, they visually looked fine and I could not identify any external damage to wires.
Still, will have to complete continuity check once I am able to confirm the ECM is for an automatic and not a manual.
Again, gonna have to wait till Monday to talk with the engine builder.
I did take a couple of pictures of the ECM so I can call the manufacture onced I am able to confirm seller.
Starting to really lean towards the engine builder putting in a manual ECM since this problem only came about a couple of days after I got the jeep back from them. To be honest, I did'nt even notice the TC not Locking up until the CEL came on. Thats when I really noticed the lack of any sort of RPM drop. I will update everyone once I find out about the ECM supplier on Monday.

As always, thanks everyone.

 

[Ken G Ford]

Uploaded some pictures I took of the replacement ECM.

 

[macleanflood]

Sure looks marked up like a rebuild... especially the tamper seal.

My guess is it's the cheapest ECU they could get.

I'd hope the shop kept your original and you could get it repaired.

-Mac

 

[hear]

Hang on, would an M/T PCM even be able to throw a P0740? I mean, the M/T computer is never going to make a request to lock up the TC, so it's unlikely it would throw the code right?

If you have good wiring and your fuses are intact (I need to trace this circuit to confirm if it is fused), I would bet the solenoid needs to be replaced.

 

[Ken G Ford]

I also looked up the PN# that's on the replacement ECM and it shows that it is for a 1997 Jeep TJ 4.0 Automatic so the ECM is probably not the issue.

Yes, probably correct in that if the ECM was a manual, it probably would never have thrown a P0740 Code.

What needs to happen is to trouble shoot the wires to and from the ECM and maybe ohm the TC Lock Out Solenoid on the 32RH itself which is what the transmission shop should have done in the 1st place.

Anyone have any idea what a good TC Lock Out should Ohm out at ?

 

[hear]

Anyone have any idea what a good TC Lock Out should Ohm out at ?

I don't, but I believe what happened on mine was that one of the wires inside the transmission had its insulation rubbed bare. The way those wires are routed they go over top of the valve body and there isn't anything preventing them from grazing the driving shell. Or maybe mine is missing a clip to keep the wires in place, idk. But one wire was bare at exactly the right spot to suggest it was being rubbed by something that rotated at a high rate of speed. IIRC my TC lockup would work if I had it plugged in with one polarity, but would not work/blow fuse/throw code (can't remember exactly what it did) if I had it plugged in with the opposite polarity. AFAIK it's the only connector on the vehicle that allows for it to be plugged in more than one polarity.

TL;DR - don't rule out the wiring inside the transmission.

 

[Ken G Ford]

Quick update from the Transmission shop.

Transmission is out of the jeep.

As was explained to me, there was a worn area in it housing where the TC Lockout solenoid is installed?

That worn area was causing it to lose pressure and not lock up?

They also noticed shavings in TC itself so are replacing the TC as well.

I'm a bit concerned about the particles in the TC since in my opinion that would also mean that those particles are also circulating through out the transmission?

 

[macleanflood]

Hopefully your transmission shop doesn't do what mine did...I paid $1000 for an AX-15 rebuild...I did all the swapping... transmission was in and out five times in two months and never worked. Ended up cancelling my CC changes and buying a new one from Advanced Adapters. Good news is I am really fast at pulling transmissions in Jeeps.

-Mac

 

[hear]

I’m trying to figure out what a “worn area in the housing” means with respect to the TC lockup solenoid. That solenoid get stuck in a hole in the valve body and stays in place with an o-ring and a screw. If that bore is worn, I would LOVE to know how it became so.

But that’s in the valve body, not the housing. In the housing would have to mean the passage that connects the VB to the housing & pump I guess?

As far as the metal shavings, I guess they’re planning on doing a fluid flush? That would probably take care of everything inside the trans. It’s standard operating procedure to change the TC in this case.

But most importantly, what are they doing to address the TC lockup “worn area?”

 

[Ken G Ford]

Hopefully I will have more detail as they are anticipating it to be completed by then. One way or another I too would like to know how they planned to address the TC lockup “worn area?” or for that matter, a better explanation if the worn area is on the Valve Body itself? I do recall when they 1st re-built it they had to replace the valve body itself with a used one
since the channel that the ball and spring fits into to ratchet gear selection had worn out and the lip of the hole the spring and ball bearing fit into had worn away on one side as the spring had become dislodged and worn away that area.
I know they struggled to find a new valve body so had to setlle on a used one.

Maybe when they found what they thought was a useable replacement valve body they did not notice an additional worn or damaged area where the pressure would eventually be lost?

Again, will post more detail once they get it resolved as I would like others out there to be able to read this and learn from as I have on many occasions with multiple other Jeep problems that I have encountered.

The Jeep Wrangler TJ Forum is PRICELESS

 

[Ken G Ford]

Picked up the TJ last Thursday.

Unfortunately, not good news. After Valve Body replacement, a new TC I got the TJ back.
Ran awesome and the shifts were buttery smooth.
I didn't notice the 150rpm drop on the HI way drive home but figured it was just me since I haven't driven the TJ in a while.
Drove it for 30 min on Saturday, and today after driving it another 30 min or so....... CEL with P0740 again! AGHHHH!!!!!!!!!

Quess its going back to the Transmission shop again on Monday since its supposed to be covered under warranty from the full rebuild.

Seems like the trouble shooting of this issue is simple. Check for low fluid, check electrical connections are solid, Ohm resistance of the solenoid itself to make sure it's good and then check the signal from the ECM to make sure the signal to lock up the TC is being sent?

Not sure why they can't seem to pinpoint the problem?

 

[hear]

When I was chasing mine down, I had toyed with the idea of adding an LED that would light whenever the solenoid was told to turn on. The idea was I wanting to know if it wasn’t being told to turn on or what. No idea if that was going to be a good idea or what.

I’m always suspicious of TJ wiring in general, but if a new TC, new solenoid, and new VB is still throwing the code, wiring & PCM are kinda the only things left it could be. The TCC wiring itself is interesting, because it’s not in the same loom as most everything else. It’s more like a heavy fabric, which I assume is because of the heat in & around the area of that wiring? IDK, but I know I’ve seen bare & melted wires there before.

Unless something crazy is going on like they used a non lockup TC or I don’t even know.

 

[Ken G Ford]

So..... mover came and my house went up for sale. Picked up the TJ from the Transmission shop after they put a new TQ on it and went through there original rebuild. The shop owners dad came out of retirement and went through it and could not find anything terrible wrong with it. He made some small adjustments and the 32RH is shifting smoother then I ever recalled it shifting......but still no TQ Lock Up and CEL is throwing the same code as before. Went for a drive with the old man and with some temporary wiring, he was able to lock up the TQ by applying some voltage to the wires. Proved to me that it is not the transmission and tat it has to be wiring and/or no signal from computer. Shippers packed up the TJ and I just drove down to my new home Austin Texas.

Next task once I find a house to buy is to go through the wiring between the transmission and the computer and Ohm the wires.
Problem is that I'm not sure which two wires at the computer side I should be looking at?
Anyone have any ideas or a schematic I can look at?

If wiring Ohms out as good then all it can be is the computer itself that is not putting out the correct signal ?

Luckily, engine builder sent me pictures of the warranty document from the PCM re-manufacture he bought it from and it still has 8 months warranty.

Anyway, just wanted to give everyone and update since you all have been nice to give me some ideas on what to look for.