Help needed diagnosing intermittent overdrive '99 Gen 2.5

nckwltn

Explorer
'99 - Gen 2.5 - 161k miles

A couple of weeks back on my way home from work, my transmission began shifting in and out of over drive, ie jumping from ~3k to ~4k. The button on the gear selector seems to work just fine. If I use the switch to disengage OD, my RPMs don't jump around and the transmission stays in gear just fine.

I immediately thought I was a bit low on tranny fluid, so that night, I checked and added about 1/2 quart. It was a little low, but not scary low.

That seemed to have resolved the issue for a few days, but the issue came back, likely didn't really go away. So began my google search for "montero|pajero overdrive problem"

I seemed to find two primary culprits, The transmission temp sensor or the overdrive solenoid. Upon visual inspection, I don't see any obvious issues.

The temp sensor is involved by not allowing OD to become active until the trans come up to temp. So if the sensor is not working properly, the trans will never appear to get up to temp.


What is strange is that during my morning drive (about 20 miles of freeway) it seems to stay in OD just fine. Car sits all day in a garage (no AC, but not in sunlight), and then about 2/3rds of my way home I start to have issues with the transmission slipping out of OD.


Any thoughts on how I can troubleshoot this issue, or where I should focus my efforts? One thought is to just ride it out until the issue becomes more consistent then try to trouble shoot further. Today, the OD totally stopped for about the last 5 mins of my drive, so it could be permanently out.

Anyone else have any similar issues?
 

nckwltn

Explorer
OD worked great all the way to work. Started cutting out about 3/4 of the way home.....

I do park on a flat surface at work, and a slight rearward decline at home.
 

RyanY

Adventurer
I seem to recall that a coolant temp sensor has some influence over whether or not O/D will engage - you might want to look in that direction.

Have you followed the diagnostic procedures in the FSM?
 

nckwltn

Explorer
I seem to recall that a coolant temp sensor has some influence over whether or not O/D will engage - you might want to look in that direction.

Have you followed the diagnostic procedures in the FSM?
I've read the same about the coolant temp sensor, I have an OBD2 reader and the temps being reported are not fluctuating that I've noticed (will monitor closely on my way home today). There is a secondary temp sensor that operates the gauge... and my gauge is working properly as well.

I am following the FSM, shorted out pin 1 on the OBD2 connector to read any transmissions specific codes, but I didn't get any codes back (just a constant fast flashing light).... I'm thinking about trying to come up with some wires running into the cab that will let me monitor the trans temp senor resistance while driving, perhaps next I'll make sure the solenoid is getting power the entire time (have also read about a relay that could be failing, but I'm not sure where it's located).


One thing about my drive is that on the way to work, I start on freeway and finish on surface streets (where I'm less likely to notice the OD not functioning), on the way back I end on freeway, so a non-functioning OD is really noticeable.
 

KyleT

Explorer
My 98 did something similar. But it also had very hard shifts from 1-2. Maybe make sure you are running SP3 or equivalent fluid. I did a flush and it fixed it immediately.


Sent from my iPhone using Tapatalk
 

nckwltn

Explorer
My 98 did something similar. But it also had very hard shifts from 1-2. Maybe make sure you are running SP3 or equivalent fluid. I did a flush and it fixed it immediately.


Sent from my iPhone using Tapatalk
I'm not sure of the fluid, but I know the PO used nothing but recommended fluids. Looking at the fluid on the dip stick, it doesn't look dark or discolored, and doesn't smell burnt. I have some SP3 that I used to top it off with.

All of that being said, I'm sure it wouldn't hurt to do a flush. Will price out some of the other components (temp sensor/OD Solenoid) and if I have to start throwing parts at it, will start with the most likely low cost option.

I've probably put 30k miles on the truck in the last 3.5 years and this is the first time it's come up.


Drove home today 70-75 mph on the freeway and no issues..... it's so intermittent, bleh
 

bikerjosh

Explorer
Luckily you won't need overdrive during the Fall DV trip. :sombrero: Of course the drive to and back won't be a ton of fun. GL w/fix.
I need to fix my AC prior to the trip.
 

nckwltn

Explorer
My 98 did something similar. But it also had very hard shifts from 1-2. Maybe make sure you are running SP3 or equivalent fluid. I did a flush and it fixed it immediately.
Ok, I'm going to backtrack a little..... on the way home today, started having my intermittent shift issues, dropped it out of OD and it was feeling like the issue was persisting (but only slightly).... so when I pulled in the drive I popped the hood, checked the fluid level. While the fluid wasn't "dark" per say, it didn't look very red.... so I checked the fluid on my 03 that I flushed about 30k ago... the contrast in colors made my 99 fluid look brown...

Looks like I'm going with a fluid flush..... now to source the SP3 for something less than the dealer price
 

TheMole

Adventurer
Ok, I'm going to backtrack a little..... on the way home today, started having my intermittent shift issues, dropped it out of OD and it was feeling like the issue was persisting (but only slightly).... so when I pulled in the drive I popped the hood, checked the fluid level. While the fluid wasn't "dark" per say, it didn't look very red.... so I checked the fluid on my 03 that I flushed about 30k ago... the contrast in colors made my 99 fluid look brown...

Looks like I'm going with a fluid flush..... now to source the SP3 for something less than the dealer price
I just ordered 12 qts of Eneos SP on ebay for about $73 shipped for a flush that I'm planning to do this weekend. Not sure how the price is compared to the Mitsu fluid, but it comes out to about $6.00/qt. Hope I didn't overpay.
 

nckwltn

Explorer
I just ordered 12 qts of Eneos SP on ebay for about $73 shipped for a flush that I'm planning to do this weekend. Not sure how the price is compared to the Mitsu fluid, but it comes out to about $6.00/qt. Hope I didn't overpay.
Looks like a good price!
 

nckwltn

Explorer
**Update

My issue isn't fully solved yet. I did do a fluid swap (just go ahead and buy a case, you'll probably need the extra 2-3 quarts because you'll end up flushing out more than the 8.9, and then you'll have to wake up at 6am to get to the dealer to buy those 3 quarts so you can get home to top the transmission off so you can get to work only a little late.... don't ask me how I know)

prior to flushing, I had pretty much lost overdrive completely. Right after the flush OD came right back (after being gone for several days of my commute).... however the I continued to slip in and out of OD.... so I put a multi meter to the engine coolant temp sensor, and verified I was reading -40 F with the sensor unplugged.... not the engine temp sensor at fault.

I also unplugged the trans fluid temp sensor (but I don't have a readout for that on my obd2, so don't know the temp).... I put a meter across the pins and did get some resistance that steadily changed as the fluid cooled.... so it's as least reading consistent with semi-warm fluid.

After fiddling with the fluid temp sensor, I had OD all the way to work and back today.... not a single (detectable) slip.... I'm wondering if my sensor is at fault, or if there might be a short in the wiring... the wiring appeared to be intact.


Will continue to monitor over the next few days.

If it isn't the temp sensor on the trans, my next troubleshooting item is the OD solenoid....
 

nckwltn

Explorer
**Update 2

day the day after I changed the fluid I had no OD to and from work.... that evening is when I checked the trans fluid temp gauge.... it seemed to be working.... but the wires did get a little jostle around.... since then I've had had OD to and from on my commute.... that's 3 days of no slipping.

I checked the fluid level tonight, and it was down a little from my measurement right after the change.... so I added 1/4 of a quart.

I'm wondering if some of the fluid passages were empty/low and look a few miles to fill up..... OR, it is my temp sensor and jiggling the wires a little and now it's getting a good connection.


Going for a longer drive this weekend, and hitting a trail... should be a good shakedown run to verify if I can cross this one off my list.
 

nckwltn

Explorer
**Update 3

I'm going to call this case closed.... did a 260 mile round trip included freeway, 4 low, lots of bumping around.... no a slip in site... had OD on the way to and from without failure.

I also noticed that at freeway speeds I seemed to have a little more lower end grunt. Normally when going up hill on these certain sections of freeway I would have trouble maintaining speed and/or having to downshift much sooner.... this time I was able to keep speed (better) and not need to downshift quite as soon.


Will continue to monitor, and am thinking about tapping into the fluid temp sensor with an in-cabin readout to know the exact temp of the fluid, seems pretty easy to add something like that.
 

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