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Discussion Starter #1 (Edited)
Over the last year, there have been multiple threads dealing with rear differential locking systems that stopped working. In several of these cases, correct operation was restored when the 4Low sensing switch on the transfer case was replaced. The 4Low switch must send a signal to the 4WD ECU confirming that the transfer case is in low range before the 4WD ECU will send a "LOCK" command to the rear diff. If the 4Low switch doesn't close and send the signal, the diff will never lock.

The question is, how and why are these switches failing, and is there anything that the owner can do to reduce the potential for switch failure?

One Forum member provided a failed 4Low switch for analysis, with interesting results.

The switch failure was caused by two factors:

1. The immediate cause was oil contamination on the internal switch contacts. There was a tiny speck of carbonized oil on the face one of the stationary contacts which created an insulating barrier between this contact and its mating contact.

The switch consists of two functional sections:

a) the plunger side, which transfers motion from the transfer case internal parts into the switch;

b) the electrical contact side, which contains the fixed and moving electrical contacts.

The two sides of the switch are isolated from each other by a rubber diaphragm which is intended to keep transfer case oil out of the electrical side. The diaphragm in this switch was in perfect condition, with no tears or pinholes. However, the oil film on the other parts of the switch housing indicated that transfer case oil had seeped around the outside edge of the diaphragm and gotten into the electrical contact chamber.

2. The contributing cause was poor design of the switch. A properly designed switch will incorporate mechanical "wiping" action as the contacts close. This wiping action tends to wipe away any oxidation or contamination on the contact surfaces, and expose bare metal to permit a low-resistance electrical interface. In this switch, there is no mechanical wiping action, and a tiny speck of carbonized oil was enough to disable the switch.

Here are the details of the analysis:

1. First, a photo of the complete switch:



2. The switch was tested to ensure that it was electrically "open" (> 1 megohm resistance) when the plunger was NOT pressed; test PASSED:



3. Next, the switch was tested to ensure that it was electrically "closed" (< 1 ohm) when the plunger was pressed. The switch still indicated an "open" condition, so it FAILED the test:



4. The potting compound and the sealing at the wire-entry points looked OK:



5. The contact pins in the connector were clean and physically undamaged:



6. The plunger tip was undamaged, and the plunger moved freely:



7. The switch housing was chucked in a lathe, and the housing was carefully cut to allow the internal components to be removed without damaging any of the parts or introducing new contamination. L>R: switch body with fixed electrical contacts, spring, moving contact plate, diaphragm, and nose of switch with plunger assy.



8. The internal portion of the plunger mechanism was OK:



9. The diaphragm was examined under a stereomicroscope, and no tears or pinholes were found:



10. The moving contact plate was oily, but the contact buttons showed no electrical erosion or carbonization:



11. The stationary contacts were oil contaminated, and one contact (LH) showed a spot of carbonized oil where it touched the moving contact:



12. Here's a close-up of the contaminated contact:



13. After cleaning off the tiny spot of carbonized oil, just setting the moving contact plate against the stationary contacts achieved a good low-resistance (< 1 ohm) electrical connection, even without the spring load from the plunger mechanism:


Since this failure was caused by oil penetrating past a seal inside the switch, there is probably little that an owner can do to prevent this type of failure except to ensure that the transfer case breather is kept clear to minimize pressure buildup inside the transfer case that might tend to force oil past the diaphragm. Normally, periodically actuating a properly-designed switch helps keep the contacts clean; with this non-wiping switch design, it's hard to tell if "exercising" the switch would help or actually accelerate the failure if the contacts were oil-contaminated.
 

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Discussion Starter #3
Great failure analysis Test

Is that arcing damage also on the LH contact?
I think those other "spots" are just little particles of debris, even though they kind of look like burn pits.

The moving contact plate is guided so its contact buttons can only touch the stationary contact at one point.

I'll take a closer look at those other spots the LH contact and see if they are pits or lumps.

(I should have taken another photomicrograph AFTER cleaning off the carbonized spot.)
 

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Nice Analysis Test, surprising amount of oil has migrated past the seal to the inside of the switch. It would be interesting to know how many of the failed switches were with gear oil changed to synthetic.
A Synthetic oils streamlined molecular structure will certainly find it's way past a somewhat marginal quality seal. Older Ester based synthetics were very hard on seals especially neoprene.
 

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Scott you in box is full, call me I still have the part.
I will be up till 10/11 est.
Mike
858 204 7085
 

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Great analysis, much appreciated as I've gone through a couple of failures. I had 2 of them fail on me, maybe 6 months apart. The first was still on the original factory tranny oil from new, the second was after the dealer did a flush. The failures were about 6 months apart. I eventually just bypassed the built in switch to a manual switch on my dash to prevent this from happening again in the future, which after seeing your analysis looks like the only permanent fix.
 

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FJtest that is a very thorough failure analysis test. (you must be an engineer)
Where on the transfer-case is the switch? (I want to check mine)
What is the acceptable resistance?
Is it accessible to change?
What is the part number ? (for an automatic)

TTFJ
 

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Nice FMEA I did the hack long ago to remove this from the system. These switches are crap!
 

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I'm having the same issue with my transfer case. I shift into 4H and no lights come on. I shifted back and forth numerous times and finally got the lights to come on...for a week or two. Now they don't work again.

Searching this forum and the net I learned a lot about the switches, particularly this thread. Very well done!

I also found this info: Lexus LX470/Toyota Landcruiser 4WD Center Differential Lock Transfer Indicator Switch Problem It's a 2000 Lexus/Toyota switch but it looks to be about the same. I'm wondering if the part number would be the same. It looks like there is two or three of these switches on the FJ. Are all three switches the same? Has anyone tried cleaning the switch? The monkeeworks post said he used simple green. I'm thinking about hitting it with MAS cleaner as it won't leave a residue. But, the info FJTest posted indicates that the electrical contacts are isolated from the moving part of the switch. Would that make cleaning it a waste of time?
 

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I didn't see a technical how to for removing transfer case switches. I observed mine but I would like to pull them out and inspect the ball mechanism.

I have 3 lights on dash, slip indicator, VSC OFF , VSC Trac. I was able to scan it and pulled C1258.....protocals says to check the transfer case switches, and the ECU....I am hoping its the switches.

I just do not know how to access them. I've read some sources that the transmission needs to come off.

anyone with hands on experience, Im all ears.
 

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Discussion Starter #11 (Edited)
FJtest that is a very thorough failure analysis test. (you must be an engineer)
Where on the transfer-case is the switch? (I want to check mine)
What is the acceptable resistance?
Is it accessible to change?
What is the part number ? (for an automatic) TTFJ
(I haven't looked at this thread for some time, and am catching up on accumulated questions.)

1. The switches are located on the side of the transfer case.
2. When the switch is OPEN, the resistance should be greater than 10 megohms; when closed, less than 1 ohm.
3. They are easily accessible with the appropriate open-end wrench.
4. There are three switches on an AT model, so you'll have to check the location vs dealer parts listing to make sure you get the correct one.
 

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I am having a similar issue with mine not going into 4wd. I’m in the military and just came back from three years overseas. My girlfriend had been driving it but never used 4wd. Now that I am back, I see no leaks and the gears have not been used. Is there an easy way to test these switches with a multimeter? Also does anyone have any idea where to buy replacement switches? I pray not the dealership. :)
 

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Discussion Starter #13
I am having a similar issue with mine not going into 4wd. I’m in the military and just came back from three years overseas. My girlfriend had been driving it but never used 4wd. Now that I am back, I see no leaks and the gears have not been used. Is there an easy way to test these switches with a multimeter? Also does anyone have any idea where to buy replacement switches? I pray not the dealership. :)
These switches can be easily tested with a good quality digital multimeter, as shown in the original post.

Disconnect the switch plug from the harness and probe the connector contacts while someone shifts the transfer case through the various ranges. Switch OPEN condition should show multi-megohm resistance, CLOSED position should show no more than a tenth of an ohm.

This is a Toyota-specific part, so as far as I know the dealer is the only option.
 

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FJ Test: Do we really need these switches, it seems like all they do is provide a signal back to the ECM for the Rear Diff loc, and the ADD to operate the front diff. What if they were just jumped out. We still have the Diff lock switch for that. Have not looked to see if there is another switch for the front diff. The transfer case operation is all manual.
 

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Discussion Starter #15
Both switches can be "bypassed" with SPST switches installed in the blank accessory switch locations. I would not recommend just permanently installing shorting jumpers across the switch connectors.
 

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Yeah I was thinking of that but did not want to run additional wiring. Are there any downsides to just using jumpers . Would they damage the in ECM any way. I want dependability not electronic overcontrol that fails at the most inopportune time. We need to look and see if operational reliability in other systems can be improved as our FJ age.
 
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