Toyota 4wd Reliability?

[bayaz]

Inside A.D.D. unit the final limit switches indicate complete engagement of the splined collar that links axle to the diff. Without full engagement signal or a fault in the electronics of the module not relaying the signal of engagement to the 4WD module. Not knowing if the A.D.D. had fully engaged the 4wd module keeps waiting for a switch signal that will never come. This will not allow you to shift into 4lo. Another symptom right? Well if you beat on it with a hammer and get intermittent communication between the two modules I would expect faulty contacts or corrosion involved within the A.D.D. You mentioned they're new though.. also your skid control module will be disabled if there is no communication with the A.D.D. module which is the possible cause of your Christmas tree lights. Like blackworks mentioned shifting to 4hi and 4lo need to be done properly to prevent hard shifting and premature wear and tear.. especially 4lo. To shift into 4lo flawlessly come to a stop on a slight incline, shift into neutral let off the brakes enough to get a slight roll and the make the shift. You really have to jam the the sh1t out of it otherwise. 4hi, slow to below 40 mph, straight, let off throttle, complete shift before using throttle again. Keep us updated this is a fun one!

Thanks. That’s the procedure I follow to engage 4H and 4L too.

As far as ADD and Christmas lights, I’m certain there’s no corrosion. I asked the mechanic each time if there was water and there was none. Moreover, the ADD motor itself was functional the second time it was replaced (Toyota said the signal being passed to ADD wasn’t being read). The current motor is only two months old, and I haven’t submerged the vehicle deep enough to flood it even if the breather failed. Further, I had weeks upon weeks of having full Christmas lights AND fully functioning 4wd. Christmas lights were fixed with a zero point calibration.

I’m curious what else goes into engaging ADD. There are 6 prongs (including ground) in the connecting harness.

As far as diff tilt/drop, I’ll be honest, I’m glad I removed it. Now the u-joints and front drive shaft are back to the stock design. U-joints have way less flexibility than the CVs. The actual “correction” to the CV angle was negligible. People who measured it, found the difference to be only 1-2 degrees. Further, I’m glad to gain back the clearance under my skid. My front skid has taken hits hard enough to sheer off 3 captive nuts and bend one of the mounting points. With a diff drop, it was sitting on spacers, reducing clearance and creating additional weak points. I’m glad the drop is gone.

 

[Jakeepoo3]

Thanks. That’s the procedure I follow to engage 4H and 4L too.

As far as ADD and Christmas lights, I’m certain there’s no corrosion. I asked the mechanic each time if there was water and there was none. Moreover, the ADD motor itself was functional the second time it was replaced (Toyota said the signal being passed to ADD wasn’t being read). The current motor is only two months old, and I haven’t submerged the vehicle deep enough to flood it even if the breather failed. Further, I had weeks upon weeks of having full Christmas lights AND fully functioning 4wd. Christmas lights were fixed with a zero point calibration.

I’m curious what else goes into engaging ADD. There are 6 prongs (including ground) in the connecting harness.

As far as diff tilt/drop, I’ll be honest, I’m glad I removed it. Now the u-joints and front drive shaft are back to the stock design. U-joints have way less flexibility than the CVs. The actual “correction” to the CV angle was negligible. People who measured it, found the difference to be only 1-2 degrees. Further, I’m glad to gain back the clearance under my skid. My front skid has taken hits hard enough to sheer off 3 captive nuts and bend one of the mounting points. With a diff drop, it was sitting on spacers, reducing clearance and creating additional weak points. I’m glad the drop is gone.

Yes correct. Your four wheel drive is functional without the skid ECU/master solenoid. But are your VSC and other abs related functions all working when the ADD module isn't? "(Toyota said the signal being passed to ADD wasn’t being read)" and the technician tested the entire circuit to pinpoint the failure point? By chance do you know if he tested the new ADD module before installation? Battery voltage alone will fry it. Here is the circuit and connector diagram attached. I reckon you could bust a multimeter out and and test the circuit and communication between modules.. Did you keep your old module? With some skill and knowledge you can open it up and inspect all the contacts and switches. Sometimes a good cleaning is the only thing wrong with it. You can also hook it up to a power source with the PROPER relay and test it yourself, Toyota won't do this though they will only replace it.

 

[KKTRD-PRO]

Dang, what a nightmare. Isn't there some sort of lemon law that can be invoked here?

 

[bayaz]

Yes correct. Your four wheel drive is functional without the skid ECU/master solenoid. But are your VSC and other abs related functions all working when the ADD module isn't? "(Toyota said the signal being passed to ADD wasn’t being read)" and the technician tested the entire circuit to pinpoint the failure point? By chance do you know if he tested the new ADD module before installation? Battery voltage alone will fry it. Here is the circuit and connector diagram attached. I reckon you could bust a multimeter out and and test the circuit and communication between modules.. Did you keep your old module? With some skill and knowledge you can open it up and inspect all the contacts and switches. Sometimes a good cleaning is the only thing wrong with it. You can also hook it up to a power source with the PROPER relay and test it yourself, Toyota won't do this though they will only replace it.

That diagram is golden. I don’t think Toyota tested it like that. All the tech did was order and install a new one and see if 4wd worked. Good because it’s speedy but bad because the issue appears to be more than just an ADD failure. I wish I asked for the old actuator, but I never did. I’d be curious to test it myself.

 

[bayaz]

Dang, what a nightmare. Isn't there some sort of lemon law that can be invoked here?

Toyota dealer was concerned about this when the actuator failed the second time. They even filed a case with Toyota HQ to report the problem. But practically speaking, I dont want them to buy back my truck. I won’t get back what it’s worth and if I were to buy a new one, I’d pay another $15-20k extra plus a wait time. I just want it fixed. I wonder if I can just trick the 4wd circuit and install a manual actuator to connect the front wheels. It seems like some people have switched to manual hubs on the 3rd gen due to the vacuum-operated ADD constantly failing.

 

[BlackWorksInc]

That diagram is golden. I don’t think Toyota tested it like that. All the tech did was order and install a new one and see if 4wd worked. Good because it’s speedy but bad because the issue appears to be more than just an ADD failure. I wish I asked for the old actuator, but I never did. I’d be curious to test it myself.

I am curious what they meant by "the signal isn't reaching the ADD," because that makes it sound like a 4WD Module issue or a wiring harness issue not sending a signal to the ADD? Which seems a bit odd to me, but I suppose is possible?

I have had to de-pin... I want to say pin#3 on the ADD and either leave it open or ground it to diagnose whether or not an issue was ADD related or not. But aside from the actual motor being driven, everything else on the connector should be an Output not an Input as it's feeding signals back to the 4WD ECU on the status and position of the actuator once it's been commanded to engage/disengage.

Dang, what a nightmare. Isn't there some sort of lemon law that can be invoked here?

Maybe? I mean this would technically be a 3rd repair attempt by Toyota... I'm not too familiar with lemon laws and that would be up to the OP if they want to pursue that option.

 

[Jakeepoo3]

I am curious what they meant by "the signal isn't reaching the ADD," because that makes it sound like a 4WD Module issue or a wiring harness issue not sending a signal to the ADD? Which seems a bit odd to me, but I suppose is possible?

I have had to de-pin... I want to say pin#3 on the ADD and either leave it open or ground it to diagnose whether or not an issue was ADD related or not. But aside from the actual motor being driven, everything else on the connector should be an Output not an Input as it's feeding signals back to the 4WD ECU on the status and position of the actuator once it's been commanded to engage/disengage.

Maybe? I mean this would technically be a 3rd repair attempt by Toyota... I'm not too familiar with lemon laws and that would be up to the OP if they want to pursue that option.

I back that. The only input at add is command to operate the motor. Maybe he said it backwards that would make a lot more sense. Or maybe he just needed to bash it with a hammer first and then check for signal to the motor well that's where I would start your diagnostic is at that connector. And this technician has f_cked with that connector that should normally never even be touched over the entire lifespan of the truck numerous times now so maybe you'll get lucky and find a pin pushed in too far or something simple like that. Don't forget to ensure good ground. This is why you test the basics first instead of replacing a module three times one after another.. those odds are astronomical..

 

[BlackWorksInc]

@Jakeepoo

Fellow scam artist dealertrash grease monkey? Lol

 

[sparkyy192]

just adding my 2 cents because nobody has mentioned it before, but have you checked the speed sensors and the wiring harnesses? I had a similar issue. Mine was caused by the lift stretching the wiring harness for the speed sensor which exposed some wire. Over time, water got in and began corroding the wire which caused intermittent shorts and finally the harness failed. Symptoms exactly like you describe.

Might not be it, but worth a look.

 

[Bmnorm2]

Thanks. That’s the procedure I follow to engage 4H and 4L too.

As far as ADD and Christmas lights, I’m certain there’s no corrosion. I asked the mechanic each time if there was water and there was none. Moreover, the ADD motor itself was functional the second time it was replaced (Toyota said the signal being passed to ADD wasn’t being read). The current motor is only two months old, and I haven’t submerged the vehicle deep enough to flood it even if the breather failed. Further, I had weeks upon weeks of having full Christmas lights AND fully functioning 4wd. Christmas lights were fixed with a zero point calibration.

I’m curious what else goes into engaging ADD. There are 6 prongs (including ground) in the connecting harness.

As far as diff tilt/drop, I’ll be honest, I’m glad I removed it. Now the u-joints and front drive shaft are back to the stock design. U-joints have way less flexibility than the CVs. The actual “correction” to the CV angle was negligible. People who measured it, found the difference to be only 1-2 degrees. Further, I’m glad to gain back the clearance under my skid. My front skid has taken hits hard enough to sheer off 3 captive nuts and bend one of the mounting points. With a diff drop, it was sitting on spacers, reducing clearance and creating additional weak points. I’m glad the drop is gone.

Agree.

I recently completed the integration validation of a driveshaft used with the drivetrain system i'm responsible for. I can confirm that U-joints have very limited flexibility and are generally required to be within 0 to -3 degrees for independent suspension and 0 to -6 degrees for solid axle type. So, 1 degrees is a huge change relative to the tolerance. A CV has a whole order of magnitude more.

 

[bayaz]

just adding my 2 cents because nobody has mentioned it before, but have you checked the speed sensors and the wiring harnesses? I had a similar issue. Mine was caused by the lift stretching the wiring harness for the speed sensor which exposed some wire. Over time, water got in and began corroding the wire which caused intermittent shorts and finally the harness failed. Symptoms exactly like you describe.

Might not be it, but worth a look.

I visually inspected the speed sensors and respective harnesses. Seem fine. I disconnected the wires from control arm / spindle when putting on the lift. Anything else I can check here based on your experience? All the ABS functions work well.

 

[bayaz]

I back that. The only input at add is command to operate the motor. Maybe he said it backwards that would make a lot more sense. Or maybe he just needed to bash it with a hammer first and then check for signal to the motor well that's where I would start your diagnostic is at that connector. And this technician has f_cked with that connector that should normally never even be touched over the entire lifespan of the truck numerous times now so maybe you'll get lucky and find a pin pushed in too far or something simple like that. Don't forget to ensure good ground. This is why you test the basics first instead of replacing a module three times one after another.. those odds are astronomical..

There’s an order to checking the ADD prongs with a multimeter, right? Do I need to remove the ADD off the diff?

 

[sparkyy192]

I visually inspected the speed sensors and respective harnesses. Seem fine. I disconnected the wires from control arm / spindle when putting on the lift. Anything else I can check here based on your experience? All the ABS functions work well.

unfortunately no. Mine also looked completely fine. Did you pull codes? Mine showed C1407 Open or Short Rear Speed Sensor RH. It was only after I replaced the harness and stripped the wiring on the old one to look at it, did I notice it was bad.

 

[bayaz]

Sounds like I need to get my code reader going.

 

[Jakeepoo3]

just adding my 2 cents because nobody has mentioned it before, but have you checked the speed sensors and the wiring harnesses? I had a similar issue. Mine was caused by the lift stretching the wiring harness for the speed sensor which exposed some wire. Over time, water got in and began corroding the wire which caused intermittent shorts and finally the harness failed. Symptoms exactly like you describe.

Might not be it, but worth a look.

That won't affect shifting back and forth from 2 to 4wd. It will in fact cause all the Christmas tree issues when his skid module is disabled that he describes. Good observation. But we have determined that symptom is due to a communication error between a.d.d. and skid module.

 

[Jakeepoo3]

There’s an order to checking the ADD prongs with a multimeter, right? Do I need to remove the ADD off the diff?

No just the connector to start.

 

[Jakeepoo3]

Sounds like I need to get my code reader going.

You don't need a scanner. You can pull codes which would be really helpful manually with what Toyota calls a sst check wire. A jumper wire In real talk. Right now at home within a few minutes. Get on that sh1t.

 

[bayaz]

You don't need a scanner. You can pull codes which would be really helpful manually with what Toyota calls a sst check wire. A jumper wire In real talk. Right now at home within a few minutes. Get on that sh1t.

Mind to elaborate? I’m confused.

 

[Jakeepoo3]

Mind to elaborate? I’m confused.

At the DLC you can jump terminals 4 and 13 with a jumper wire THAT FITS NICELY. *Carefully do not damage/spread terminals*. Turn key to the on position. The CEL, VSC, ABS, etc. lights will blink all your codes in a readable pattern. Different lights represent the category the code falls under. You can look up the procedure and how to read the blink patterns on the internet pretty easily.

I repeat
*CAREFULLY jumping the wrong terminals can cause electrical damage, don't f_ck up your DLC connector by pushing in or over spreading terminals*

Use the same caution with the add connector and examine it for related damage when you decide to begin testing the circuit..

 

[BlackWorksInc]

At the DLC you can jump terminals 4 and 13 with a jumper wire THAT FITS NICELY. *Carefully do not damage/spread terminals*. Turn key to the on position. The CEL, VSC, ABS, etc. lights will blink all your codes in a readable pattern. Different lights represent the category the code falls under. You can look up the procedure and how to read the blink patterns on the internet pretty easily.

I repeat
*CAREFULLY jumping the wrong terminals can cause electrical damage, don't f_ck up your DLC connector by pushing in or over spreading terminals*

Use the same caution with the add connector and examine it for related damage when you decide to begin testing the circuit..

I second the warnings above.

Make sure you're looking at the connector in the right orientation... last thing you wanna do is short a CAN Bus.