Transfer Case, Center Diff Lock and Rear Diff Lock Issues and Resolution (1 Viewer)

Sep 19, 2020
I apologize if this is a regurgitation of old information, but I wasn't able to find a single post that compiled all of the issues I had to resolve my rear locker engagement. This is my attempt to give back to this forum.

Here's a little background. I am totally new to LCs and I'm a "city boy". Went out one weekend with a buddy of mine @siphanracing onto some trails and camped out deep in the national forest. Long story short, I got hooked. I went out and purchased a 100 series LC model year 1999 a few months back. I purchased it knowing the rear locker was not engaging, but for the price I paid, I couldn't turn it down.

I lagged on getting to work on the rear locker issue, but once I started, I carried the momentum until I resolved it. Thanks to @siphanracing and all of the previous users on this forum who submitted their input on the center diff lock, transfer case and rear diff lock.

Lets get to the details:

First and foremost, I had to figure out the requirements to engage the rear lockers. This was a bit tricky because many posts only explain the process on how to engage the rear locker without details on what happens during the process. Let me summarize my understanding of the requirements:

  1. The ignition must be in the ON position (motor can be on or off)
  2. Transfer case must be in 4Low position. There is a position switch on the transfer case that detects 4Low is engaged. The 12 volt signal goes through the switch and returns back to the control module to indicate engagement.
  3. When the transfer case is placed in 4Low, the center diff lock (CDL) automatically engages. You'll hear a relay click in the front dash area which engages the CDL solenoid under the vehicle (solenoid will make a winding sound when engaging).
  4. When the CDL engages, the position switch (same type of switch as the transfer case switch for 4Low) for the CDL will pull and allow the readback signal to be active. This will be read back by the control module(s) and cause the instrument cluster indicator for the CDL to illuminate.
  5. At this point, the rear locker can be engaged by turning the rear locker control knob located on the front dash. You'll hear a relay click from the rear locker control module (the module is located behind the passenger kick panel) and the rear locker solenoid (located at the rear diff) will wind just like the CDL solenoid did.
  6. The rear diff indicator on the instrument cluster will begin flashing as soon as the rear diff control switch is turned to the engagement position. It will only go solid once the locker has physically engaged. You'll also hear a loud "ping" when it physically engages.
  7. End of procedure.

I didn't know these requirements before I started troubleshooting. I read a bunch of posts and watched a bunch of YouTube videos that discussed various potential issues/resolutions. Here's a list with some links where helpful:

  1. Rear diff locker needs refurbishment
  2. CDL indicator not illuminating even though it physically engaged
  3. Pin 7 mod for CDL
  4. Go onto gravel and engage the rear diff lock and then do S-turns
  5. Lift the rear end and engage the rear diff lock and spin the rear wheels while in neutral
How I resolved my issue:
I checked all of the items above against my vehicle and for the most part, they had nothing to do with my issue except #2. My issue turned out to be the position switches for the 4Low, CDL and rear diff lock. I figured it out by taking the time to understand the engagement requirements with the help of the rear diff lock diagram that @Ayune provided in one of his posts (see below). Once I understood the requirements, I took my volt meter and measured the voltages at the rear diff lock control module.

When I placed the transfer case into 4Low, the CDL did not engage automatically. I removed the position switch from the transfer case and ohm'd the switch's two pins when the switch was pressed in. It read OPEN. These switches are cheap to buy off Amazon, but I didn't want to wait. I don't know the mechanical design of the switch, but I figured it wasn't working because of some corrosion build up within the switch contacts. Without opening up the switch, I figured I could get the corrosion off by actuating the switch continuously. I banged the switch button several times on the concrete and remeasured the two pins. The meter started to read several Meg ohms. I knew I was getting somewhere so I banged it more and eventually the reading dropped to a few ohms. I plugged the switch back into the transfer case and voila, the CDL automatically engaged. Saved myself $15.50.

However, I was not home free. The CDL indicator did not illuminate on the instrument cluster. I found several threads on the CDL position switch and holy smokes, the switch is the same as the transfer case switch. I did the same banging of the switch and fixed it. Now I've saved $31. The indicator illuminated.

I turned the rear locker control knob and I hear "click" and "hiss". Finally, more progress. The rear end was already on jack stands so I rotated the rear tires by hand and "ping!!", it locked. But wait, there's more. The rear locker indicator was still flashing on the instrument cluster. Turned out the position switch needed to get banged up as well (saved another $15.50 :cool:). Installed everything back and it all worked!! I was pretty ecstatic at this point.

That's the end of my write-up. Hope it can help other users in the future. Now, I'm ready to do some overlanding!!

Last edited:
Sep 19, 2020
You do not mention the CDL switch on the dash, you don't have one?
My 2000 has one and know on up thru 2007 do also.
The CDL switch is on my dash. It would engage when pressed, but it wouldn't automatically engage when in 4low.

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