Help needed diagnosing intermittent overdrive '99 Gen 2.5

[nckwltn]

I connected a multi meter to the TCU harnesses, when I lost OD (aka 4th gear) the computer was telling it to not shift. So I concluded it wasn't a mechanical issue with the trans, but something telling the computer not to shift, or something with the computer flaking out and not telling the trans to shift.

I think gen 3s have a 5 speed trans

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[yatin_ash]

Yes its a five speed triptronic & shifts smooth till the 5th gear around town. Its the freeway where it does but takes forever to shift into the 5th gear. 70 mph @ 3000 rpm.
I was more into torque convertor cause its a rebuilt transmission with 10k or so miles. I hear a lite ticking sound underneath after I park. My Jeep also makes that noise but its quite convincing of just exhaling the heat through the metal components. Now that you mentioned, technically it makes more sense & I'll try the TCM before anything.

hopefully this weekend.

 

[nckwltn]

Yes its a five speed triptronic & shifts smooth till the 5th gear around town. Its the freeway where it does but takes forever to shift into the 5th gear. 70 mph @ 3000 rpm.
I was more into torque convertor cause its a rebuilt transmission with 10k or so miles. I hear a lite ticking sound underneath after I park. My Jeep also makes that noise but its quite convincing of just exhaling the heat through the metal components. Now that you mentioned, technically it makes more sense & I'll try the TCM before anything.

hopefully this weekend.

If you check the FSM you should be able to find the pinout for the TCU. The gen 2 has 2 pins for shifting and one for the OD solenoid. You can read the voltage with a multimeter and know exactly what the computer is telling the trans to do.

Now,if the computer is getting bad signals from it's various inputs (speed, temp, etc), it could be telling the trans to act funny, but you can also check the voltages and resistance on the inputs to get an idea of those inputs.

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[yatin_ash]

I was able to read the transmission behavior on a professional scanner again & it does show that the TCM is telling the trans to shift into overdrive. I'm not sure if it will be smart of me to tear everything down to get to the TCM. The scanner also says the overdrive is kicking in, I'm not sure what to do next ?!

Every now & then the cruise control lights comes on when I turn the key on (I'm 110% sure I left it off). I'm not sure if that indicates something cause cruise control does work. is this an electrical short ? I don't think I've a fuse or relay for Overdrive like the Gen 2.

Any ideas ?

 

[nckwltn]

I would think that if the TCM is telling the trans to go into OD and it isn't going, it is probably something with the trans.

On the gen 2.5 there are 3 shift solenoids that are replaceable. Might be similar on the gen 3. You can read the resistance across the solenoid terminals to know if any one of them are at fault

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[yatin_ash]

fluids & solenoids was the first thing I checked. I've decided to tear it down for any electrical shorts, I might as well look at the TCM. I agree with you but that's the last thing I wanna do considering it is the most expensive part of troubleshooting this prob.

keep you posted.

 

[yatin_ash]

It took me a while but here it goes & I hope it helps someone else in this situation...

I went through every possible troubleshooting option for No overdrive till I decided to drop the transmission. Sure enough my clutch was burned & torque converter was shot. I ended up replacing it with a rebuilt one. Now I was trying to find why is a converter shot on a rebuilt transmission (by previous owner) with the right fluids & perfectly functioning solenoids & electrical components involved. It was an interesting find that the catalytic converter which is a Y pipe runs right next to the transmission. A failing catalytic causes the transmission oil to boil resulting in malfunction of internal components. A catalytic converter starts functioning at 400-600 F & shoots to 1200-1600 F & up as the amount of pollutants go up. I kept getting p0741 for TCC stuck off which means the damage was already done & after months it threw p0421 for the bank2 cat. Maybe the previous owner did get the cat code but cleared/ignored it till it shot his whole transmission.
If anyone is in this situation it is worth spending 5 mins on your catalytic with a $20 heat gun.

I ain't no pro but every mechanic & random person in US always told me Montero's are prone to transmission problems. It probably is true cause of this carb complaint catalytic. The forums from australia/new zealand & everywhere else say this is almost a bullet proof transmission. I think they are right cause replacing the catalytic with a straight pipe for more horsepower is part of basic mods for them.

Again you might have a problem as simple as @nckwltn with the TCU on a Gen 2.5

Mine is a Gen 3 2002 Montero LTD.

 

[nckwltn]

A torque converter and clutch problem? Sounds like a real nightmare!

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