Hi. I have 2002 Montero Limited with 128k miles on it. Whenever I switch to 4x4 I get this annoying high pitch noise coming from the front of the vehicle. Noise intensifies as I go faster. Changed oil in differentials and transfer case hoping noise would go away but it is still there.
Also I can switch from 2H --> 4H on the fly, however to switch back to 2H I have to stop the car, move it in neutral and then switch to 2H.
Both problems could be related to the same component failure since they both started happening at the same time.
Can you guys shed some light on what could be a problem?

 

Sounds like there's improper gear adjustment inside the front differential, or a damaged gear. When you changed the differential oils, what weight and spec did you use? What colour was the old oil you drained out?

 

I've got oil from local Mitsu dealer. DIAQUEEN SAE90 GL-5 for both diffs and 75W90 GL-4 for transfer case. Old oil in front diff and transfer case looked very clean, I was kind of surprised. Only rear diff had a dark oil. Wouldn't be the noise muffled (humming), instead of high pitch, if it was bad gears since they run in a thick oil?. Any way to troubleshoot diff problems besides replacing it?

 

some mechanical noise is quite normal.

 

I wish I was as optimistic as you are. My truck started having more problems with 4WD yesterday. All 4WD indicator lights went off and only C/D lock light was flashing. From what I read on forums bad transfer case switch or connection to the ECU might be the culprit.
Do you know where is the ECU located in 2002 Monteros?

 

Never mind I found ECU. I read error codes, 21 and 22 showed up which are accelerator pedal position sensor and transfer case front shaft speed sensor respectively. Don't know if any of these would cause C/D light flashing.

 

the only thing thats gonna cause those codes is a failing switch (or switches) on the transfer case.
there are 5 of them. You need to know what you're doing to diagnose them. You need to know how the system works, unless you wanna replace all 5 (not a bad idea).
They are NOT all the same.

 

I found nice article on how 4WD system works in Monteros. You can find it here: http://www.rsgear.com/articles/1997_11.pdf , veeeery helpfull.
There is one more switch located in front diff (freewheel engage switch) that might be the culprit too. My C/D light flashes only when I'm driving in 4H, 2H has no problem. If you look at the chart, figure 3, you will find that two switches are engaged in 2H, 2-4 fork and High/Low detection. So they are OK. According to chart there is three switches engaged when in 4H : 2-4 rail, freewheel engage and High/Low detection.
Looks like freewheel engage or 2-4 rail switch is failing.

Could you verify that the chart, (figure 3), in the article applies to 2001 and newer Monteros?

 

nope. that chart is for the previous gen monteros. although basically the same, the new monteros uses an electronic shift motor. there is no direct connection between the lever and the transfer case (at least on the 5 speed model.. there was a 4 speed "cheapo" montero in 01-02 that used a 4 speed auto and the 2/4WD transfer case from the montero sport.).

 

I know article is about previous generation Monteros. However, since the chart is basically the same, it could be used for troubleshooting 2002 Montero transfer case switches, right?