Differential lock ECU

[eastoak]

I'm troubleshooting the rear locker on my 1996, it doesn't lock and when I switch it on I don't hear the relay click like I do with the front locker. I did some of the troubleshooting detailed in the FSM and before I make the next move, possibly buying a new differential ECU, I wanted to check in here.



I did all of these tests with the exception of the vehicle speed sensor, all were good.

these tests is where i had some problems. the test where the 1 and 3 pins are connected then the switch position moved from OFF -> RR then RR -> OFF did not give me any value at all, the minus sign on my meter flickered off and on randomly but the value remained at zero. the same test for the front locker did show a value of 11.9 volts. the next test i did was the number 2 pin to ground (pin #13). that was supposed to give a value of .5 volts or less. it gave 1.4, 4.5, 12 then back to 4 and 1, wildly fluctuating values.

i have power at the switch, relay, fuse, and going into the ECU but not coming out of the ECU. the front and center lockers work reliably every time.

question: can the ECU go partially bad like this or does it either work or not work?

 

[TossYoda]

Have you pulled the rear locker itself, opened it up and checked it mechanically and electrically inside? You can also wire it up on the bench and verify it's working. If you go this route, read extensively posts here first, how to pull it without losing the 'clock' position and how to clean and reseal it, and how to reclock it if needed.
Have you checked the ground points and made sure they're clean and conducting?

 

[eastoak]

Have you pulled the rear locker itself, opened it up and checked it mechanically and electrically inside? You can also wire it up on the bench and verify it's working. If you go this route, read extensively posts here first, how to pull it without losing the 'clock' position and how to clean and reseal it, and how to reclock it if needed.
Have you checked the ground points and made sure they're clean and conducting?

i have not opened it up, I was going to after I traced the power from the switch to the ECU. Since the ECU tests didn't all check out I stopped there. The ground connection from the ECU checked out, if that's what you mean. I saw a vendor selling ECUs with a core charge so I wonder if someone out there is fixing them? If a different ECU solves my problem I'll probably open up the one I have just out of curiosity.

 

[landcrshr]

i have not opened it up, I was going to after I traced the power from the switch to the ECU. Since the ECU tests didn't all check out I stopped there. The ground connection from the ECU checked out, if that's what you mean. I saw a vendor selling ECUs with a core charge so I wonder if someone out there is fixing them? If a different ECU solves my problem I'll probably open up the one I have just out of curiosity.

I have the means to test and repair your ECU, and I'm not too far from you, if you'd like to get it to me.

 

[thabruiser]

Before I replace anything, I would continue the steps after this in the FSM on page SA-105, activating the lock motor manually. See if it's froze up, or otherwise just inoperable. I know that your tests have indicated that the ECU has taken a dump, and it is possible. But I have been bitten in the butt a couple times by throwing an ECU at a vehicle, because a FSM test indicated the ECU was at fault. Again, it is possible. But Toyota ECU's are robust, and rarely go bad. Whenever I go into a diag. situation anymore, the first thing I say is "well it's not going to be the ECU." haha. Occasionally it does need the ECU, but I give every reason to myself and my customer why. (i.e.-I checked wiring, it was good, I checked the motors themselves, they moved freely when manually actuated, I checked each switch, and they gave the proper readings. The ECu is just not sending out the voltage when receiving the input.) Oh and something Toyota suggests sometimes is "replace with known good part." haha. Hope you figure it out! Good Luck.

 

[ariff]

I can tell you I had the exact same issues as you did with my 93.. Front would lock and I heard the relays click, but the rear would not lock and I never heard the relays click. Naturally I thought it was the ECU. Until I decided to pull the rear actuator and found this:

Good news is that I was able to clean everything out and replace the brushes and the actuator worked just fine.. And I now hear the relays click when locking the rear locker.. So You may want to pull your actuator and have a look at what is going on inside there.. Good luck!

 

[eastoak]

I will take the actuator off and check it out before I do anything else. It is supposed to be removed in the locked position but I’ve read on these boards that it is possible to remove and reinstall in the not locked position. I’ll post up whatever I find, have the day off today and my girls are at school so I can work on this without being interrupted.

 

[eastoak]

I have the means to test and repair your ECU, and I'm not too far from you, if you'd like to get it to me.

Are you in the Bay Area? I’ll send you a PM.

 

[Tools R Us]

The relay is switched on both legs, power from the locker switch and ground from the position switch in the actuator. Often, when the relay doesn't click it's a ground problem at the position switch. Test for good ground at term 10 (green/yellow wire) at the lock ECU and/or term 3 at the actuator plug.

One test is; with everything hooked up and the locker switched on, briefly touch ground to term 10 at the ECU. If this is the problem the relay should click in. Warning; the purpose of the position switch is to prevent the actuator from running out of it's designed range, excessively doing this can jam it.

Sometimes when this is done, the actuator will run, and the movement is enough to somewhat clean the switch contacts, restoring it to working order. Running it a few times will additionally clean it, but if this is the problem, likely the actuator needs to come apart and be cleaned/greased for long term reliability.

 

[eastoak]

The relay is switched on both legs, power from the locker switch and ground from the position switch in the actuator. Often, when the relay doesn't click it's a ground problem at the position switch. Test for good ground at term 10 (green/yellow wire) at the lock ECU and/or term 3 at the actuator plug.

One test is; with everything hooked up and the locker switched on, briefly touch ground to term 10 at the ECU. If this is the problem the relay should click in. Warning; the purpose of the position switch is to prevent the actuator from running out of it's designed range, excessively doing this can jam it.

Sometimes when this is done, the actuator will run, and the movement is enough to somewhat clean the switch contacts, restoring it to working order. Running it a few times will additionally clean it, but if this is the problem, likely the actuator needs to come apart and be cleaned/greased for long term reliability.

Thank you, I’m about to run the test you suggested.

 

[eastoak]

The relay is switched on both legs, power from the locker switch and ground from the position switch in the actuator. Often, when the relay doesn't click it's a ground problem at the position switch. Test for good ground at term 10 (green/yellow wire) at the lock ECU and/or term 3 at the actuator plug.

One test is; with everything hooked up and the locker switched on, briefly touch ground to term 10 at the ECU. If this is the problem the relay should click in. Warning; the purpose of the position switch is to prevent the actuator from running out of it's designed range, excessively doing this can jam it.

Sometimes when this is done, the actuator will run, and the movement is enough to somewhat clean the switch contacts, restoring it to working order. Running it a few times will additionally clean it, but if this is the problem, likely the actuator needs to come apart and be cleaned/greased for long term reliability.

I back pinned terminal 10 and 13, briefly touched them and nothing happened at first so I adjusted the pins then heard a buzzing from the ecu. I found that simply putting the pin in terminal 10 alone will make it buzz.

 

[Tools R Us]

I back pinned terminal 10 and 13, briefly touched them and nothing happened at first so I adjusted the pins then heard a buzzing from the ecu. ...

Relay buzzing is usually an indication of poor connection, not enough juice to fully close it, or a bad relay.

I found that simply putting the pin in terminal 10 alone will make it buzz.

Maybe an indication of poor connection? I would remove the board from the box and inspect the connector/trace related to term 10?

 

[eastoak]

@Tools R Us will there be constant voltage at the plug when the

Relay buzzing is usually an indication of poor connection, not enough juice to fully close it, or a bad relay.



Maybe an indication of poor connection? I would remove the board from the box and inspect the connector/trace related to term 10?

a member on here who lives near me is going to take a look at the ecu while I deal with the actuator. I’ll report what I find, if anything. I really appreciate all of the help from you and everyone else who has contributed.

 

[TossYoda]

@Tools R Us will there be constant voltage at the plug when the

a member on here who lives near me is going to take a look at the ecu while I deal with the actuator. I’ll report what I find, if anything. I really appreciate all of the help from you and everyone else who has contributed.

pretty sure you're going to find actuator issues
they can look horrendous and then cleaned up and sealed work great again
I think Wits End sells a little rebuild kit.
Wits' End

 

[eastoak]

Update:

Most everyone who chimed in on this thread was right, the ECU checked out fine and the actuator itself did not.

the breather tube was completely clogged with dirt.

the magnets were loose but did not fall out. there is very little rust, mostly sand and grime holding everything fast. i'm trying to decide if i should buy and new one or rebuild this one before i have to go to work on monday...

 

[Tools R Us]

that's a mess!

 

[eastoak]

that's a mess!

it's cleaning up but I went ahead and ordered a new actuator just in case I can't get this one going by monday. how does the spring mechanism come apart?

 

[eastoak]

I got the new actuator today and mounted it up enough to be able to drive to work tomorrow but short of putting any FIPG or threadlocker anywhere. When I plugged it in it did go to the lock position but wouldn't unlock so I think there may be some issue with having removed the old one in the unlocked position, I ran out of time and daylight trying to figure it out. another issue i discovered was the vent tube being blocked somewhere, i couldn't get air flow in or out of the tube. I chased the tube up and back towards the rear driver side then pulled hard and it came free. maybe there is a valve up there somewhere but once it was free i was able to draw air through it.

 

[Rifleman]

Before I replace anything, I would continue the steps after this in the FSM on page SA-105, activating the lock motor manually. See if it's froze up, or otherwise just inoperable. I know that your tests have indicated that the ECU has taken a dump, and it is possible. But I have been bitten in the butt a couple times by throwing an ECU at a vehicle, because a FSM test indicated the ECU was at fault. Again, it is possible. But Toyota ECU's are robust, and rarely go bad. Whenever I go into a diag. situation anymore, the first thing I say is "well it's not going to be the ECU." haha. Occasionally it does need the ECU, but I give every reason to myself and my customer why. (i.e.-I checked wiring, it was good, I checked the motors themselves, they moved freely when manually actuated, I checked each switch, and they gave the proper readings. The ECu is just not sending out the voltage when receiving the input.) Oh and something Toyota suggests sometimes is "replace with known good part." haha. Hope you figure it out! Good Luck.

One of the more common problems I've found while running down electrical problems with computer controlled cars is loose, or corroded grounds causing intermittent connections, and there are a TON of electrical grounds on computer controlled cars.

 

[eastoak]

One of the more common problems I've found while running down electrical problems with computer controlled cars is loose, or corroded grounds causing intermittent connections, and there are a TON of electrical grounds on computer controlled cars.

the ground checks out and so does the ECU which i had tested by a professional, i think the shaft has to be at a certain length when it is installed for it to work right.