97 FZJ80 Locker ECU Confusion (2 Viewers)

[Skidpad13]

Ok guys, sorry to ask a question asked so many times before in different ways. When I got my 1997 FZJ80 I knew ahead of time that the lockers would not engage so I'm cool with tracking it down but now that I've read through numerous posts and searched every way I can think of I'm coming asking for help. Here's what my symptoms are and what I've done so far.

1. Checked the DIFF fuse and replaced for good measure
2. Made sure that the FR and RR lights flash on the dash when I turn the Diff Lock Switch Clockwise (they do flash)
3. I replaced the transfer case low range switch as the previous one was showing no continuity when pressed.
4. I cleaned the contacts that connect to the above mentioned switch
5. Tested the low range, slow speed, in the grass doing figure eights. Nothing.
6. Installed the dash mounted center diff lock (CDL) switch per everyone's recommendation
7. Pressed the CDL switch with the key in the on but not started position; no center diff light on dash
8. Pressed the CDL switch with the key in the on but not started position while listening for relay engagement at driver's left foot area as well as under the truck for center actuator noise. Neither of these made a sound.

So, given the investigation so far I'm thinking (per the FSM) that the next place to check is the Diff Lock ECU.
After reading the SLEE writeup on the 7-pin mod, I'm going to assume that the Diff Lock ECU and the Transmission Relay (Part # 89531-60010) are the same thing.
Now, per the FSM page below I want to check the relay/ECU.
1st I get to the ECU behind the ABS computer and then I unplug the wiring harness from it to perform the following test.
However (and I know this is a dumb question but indulge my the color-by-numbers approach) I'm going to assume that on each of these pin tests the Body ground they are referring to is PIN 13 and not a lead connected to a longer test wire that is grounded out to the body, correct?
In other words, if I want to check voltage of the center diff in the non-engaged position, I put one lead from the meter on pin 13 of the wiring harness that connects to the relay/ECU and the other lead on pin 15.
Am I correct?
Yes, I've used a multimeter for years but I want to confirm the basics for those that may be reading this for the first time. So, for example, in this case I should see somewhere around 12 volts DC if the center diff is not engaged, right?
Any insights, comments, useful criticism (haha), etc... will be truly appreciated.
Once I get past the ECU and can get a reliable confirmation that I have the voltage getting there then I feel like I'll be ready to move onto actuators if it comes to that.

I have not replaced the fusible link yet but I may do that as a matter of course despite what these tests tell me.

Thanks for your help everyone.

 

[Rwhat]

Did you confirm they are locking axles?

 

[Skidpad13]

Did you confirm they are locking axles?

Good question; I should have clarified. Yes: confirmed factory triple locked and have visually verified the actuators are on each axle. My initial hill to climb is getting the center diff to engage.

 

[WCBlueSky]

I had a similar issue and went through similar troubleshooting. One thing to keep in mind is that the ground for the center diff lock circuit is inside the actuator motor on the transfer case. If the metal wipers in the actuator motor are not making contact with ground then nothing (including the relays in the ECU) works. Once I took apart the motor the issue was obvious: some of the sticky black sealant had leaked onto the contact plate. I cleaned up the motor, regreased it, and it works perfect now.

Here is the cleaned up plate:

 

[Skidpad13]

I had a similar issue and went through similar troubleshooting. One thing to keep in mind is that the ground for the center diff lock circuit is inside the actuator motor on the transfer case. If the metal wipers in the actuator motor are not making contact with ground then nothing (including the relays in the ECU) works. Once I took apart the motor the issue was obvious: some of the sticky black sealant had leaked onto the contact plate. I cleaned up the motor, regreased it, and it works perfect now.

Here is the cleaned up plate:

View attachment 2867392

Thanks for this insight! I can't say that I'd have made that jump before thoroughly dissecting the ECU. Now I know what I'll be doing this weekend. Any tips on getting the actuator off from the top of the case other than disconnecting electronics & unbolting?

 

[Njck22]

I have a 95 that the original owner never even knew what diff locks were/ that his land cruiser had them. Front locker would not light up/engage. fixed it by disconnecting and reconnecting the connector on the passenger fender. simplest thing first and all that.

 

[Skidpad13]

Njck, when you say connector on the passenger fender, can you clarify? Not the ECU since that's on the driver's side, at least it is on mine. Thanks!

 

[WCBlueSky]

There are two diff lock ECUs: one controls the center diff and the other controls the front/rear lockers. I believe the center is on the driver's side, the other on the passenger side. You can check the voltage and relays in the ECU, sometimes the relays do go bad. Can look in the EWD to see all the connections.

 

[Njck22]

Njck, when you say connector on the passenger fender, can you clarify? Not the ECU since that's on the driver's side, at least it is on mine. Thanks!

I’m refering to the wiring harness connector in the engine bay area. It link the subharness(that goes down to the axle) to the main harness that lies on the fender

The diff lock ecu is by the passengers footwell. It’s dead simple (two high quality omron relays and a IC), so it’s probably not the issue.

 

[Skidpad13]

Got it, I totally understand now. Thanks! After thinking it through I think I'm going to start checking the relays individually & may also use a 12v source to apply voltage directly to the transfer case actuator motor. If I can get it to operate by direct application of voltage then at least I can leave it until last if nothing else works. Thanks again!

 

[Skidpad13]

UPDATE: So, I'm a very linear thinker most of the time. As I looked through the FSM I kept wondering why the Center Diff was so marginally represented in the section on the front & rear lockers. In my mind they would all three be documented together. Not so.
In the transfer case section I've just found the diagnostic info I've been searching for. Here it is below. I hope this helps others who may have faced, or will face, this seemingly common issue.

 

[TXLX100]

Is this problem fixed? I have a 1996 that it appears power not getting to front or rear lockers. I was able to move the rear locker with separate 12v power… the truck harness will not actuate it. Same for front locker. I went ahead and replaced the position sensor / switch on each axle as they were no continuity.

The CDL engages in low, the locker lights just blink and lockers never engage. The system worked 6 months ago, fwiw.

The “diff” 30amp fuse is good. Not sure where to start now…. Sounds like I need to test at the ECU(s).

 

[Skidpad13]

With the holidays I haven't gotten back to this on mine. However, from what I've learned the front & rear diffs have a separate ECU apart from the Center Diff Lock motor. If you're able to actuate it from a direct 12v source at the rear locker motor I'd test the ECU/relay. The other thing it could be is wiring so test for continuity if the ECU tests ok.

 

[Skidpad13]

Here's the troubleshooting bit from the FSM

 

[Skidpad13]

Other 2 pages specifying how to test the ECU. Good luck!

 

[Dave 2000]

Just a thought, the axle locks could be engaging but the contacts inside the locker that tell the ECU to stop flashing the dash lights may be bad?

Regards

Dave

 

[TXLX100]

Just a thought, the axle locks could be engaging but the contacts inside the locker that tell the ECU to stop flashing the dash lights may be bad?

Regards

Dave

Do you mean the position switch sensor on the axle? It’s separate from the locker, very easy to test and replace.

 

[Dave 2000]

Not had to look at them until I found a couple of days ago mine was not engaging, I had been driving around on the country campo tracks, can't do anything else until my licence is returned and found mine was engaging (front scrabbling on hard turn), but the light was still flashing indicating it had not engaged.

Regards

Dave

 

[TXLX100]

Sounds like it needs a position switch. 27mm and unscrew it from housing. You can continuity test it while depressing the spring.

 

[Zhowardfzj80]

I have a 95 that the original owner never even knew what diff locks were/ that his land cruiser had them. Front locker would not light up/engage. fixed it by disconnecting and reconnecting the connector on the passenger fender. simplest thing first and all that.

But the rear worked before unpluggin?