Need help doing diagnostic on push button 4x4..experts needed!

Hey guys, long time lurker, first time poster...

I am helping out a friend with his 2001 tacoma with the 5vz. The problem is the 4x4 does not work. When you push the 4H button on the T-case shifter, the light does not go on, nor do I hear a sound from either actuator.

I tested everything a few months ago and had no luck, I bought a new 4WD ECU because one of the chips did seem burnt lightly( but maybe it wasnt.. heard to tell) but the new ECU didnt help any part of the situation.

The 4wd Button on the shifter does work and has continuity.


I have access to the professional version of alldata but it only gave limited information. Also the 4WD ECU is not available with my autel scantool either (MS906TS...Not a total slouch of a scanner). I did go through and do some testing on the actuators and the 4WD ECU provided by alldata and I will post them below. Any help on this siltation would be appreciated, this push button setup was only on two years of tacoma so information is sparse.

I am guessing the ADD has failed, which in turn would not turn on the 4x4 light or actuate the TC actuator but I would rather ask than shot gun an ADD at it.

 

I haven't studied the 1st gen 4wd system too closely but I do know the 2nd gen system fairly well, looks pretty similar so I can try to help here.
I'm not sure how the 1st gen system behaves when a fault is present, 2nd gens flash the 4wd and/or L4 lights when a fault is present.

The best I can decipher from your tests it looks like your issue is gona be in the Transfer Case Actuator or circuits, by the voltages I'm thinking it's stuck.

 

Gotcha, is that because it actuates the TC actuator first, then the ADD?

I am not sure on how to read a fault on this, I have no action from the 4wd light. I did pull the cluster and tested the 4WD light on the dash does light up.

Thanks for your reply!

 

The Transfer Case is always shifted before the ADD so the Transfer Case has to complete it's shift before the 4wd ECU will attempt to shift the ADD.
Do you have access to a clamp on DC amp meter?
If so put it around Pin 13(Blue) or Pin 26 (Yellow/Black) at the 4wd ECU and see what the current is when attempting a shift, if you see a high current but get no movement from actuator then most likely it's stuck either from not being used or from getting water in it.

Like I said I'm not sure how the 1st gen system behaves during a shift or when there's a fault, 2nd gens flash the light during a shift (or if a fault is detected) and it stays on once the shift is complete.
I do know there is no way to check faults on 1st and 2nd gens so everything has to be checked manually, 3rd gens are capable of talking to a scan tool and generating fault codes.

 

your the man. I do have an amp clamp. I will do some testing and report back!

 

I did some testing today.

Pin 13 goes to 1.1 amps when the 4H button is pushed, then drops back to zero
Pin 26 goes to 1.4 amps when the 4H button is pushed, then drops back to zero.

So its sending out current.. but is it supposed to maintain that current? Or is it turning off because the TC actuator is not moving? It would make sense it would try to "protect" its self if the actuator does not move.

The T case actuator looks to be in good shape, the wire end of the connector looks in good shape and so do the pins. actuator pins are clean as well. Sounding like the actuator is going to have to come apart to me. not a big deal

 

Doesn't really seem like locked motor current but the fact that there's current going through the motor but it's not moving suggests the circuit is intact but there's a problem with the motor.

I believe it times out if it doesn't see movement from the actuator yes.

Not sure if it's like 2nd gens but on them you have to note the timing of it when you take it apart.

 

Did you make any progress in diagnosing this?

 

Yes I did make some progress. I took the transfer case actuator off. It was clean on the inside and at the wiring connector. The actuator operated both ways when tested with a relay. It has to be somewhere in the wiring. I did test the 6 pin connector that plugs into the TC actuator. The max voltage I got was 9.6V. Not enough to operate the actuator I presume. The connector did have continuity with ground to the battery. I put an amp clamp on each of the 5 wires, and all of the wires at one time and only got .01 amps max. I am thinking an issue with the wire harness maybe?

 

On which pins?

What pins of it are you talking about?

Pin 3 (Yellow/Red) and Pin 6 (Purple) should have battery voltage with the key on and connector unplugged.
Pin 4 (White/Black) should be ground.

The ECU only sends power to the motor when you attempt a shift, it will time out after a few seconds if it doesn't see movement from the actuator.
If it's like a 2nd gen it's not gona do anything with the connector unplugged.