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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4728
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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I'm a failure analyst company and very capable mechanic have

Customer Question

I'm a failure analyst for helicopter company and very capable mechanic have replaced just about everything in cars trucks and boats. I need a toyota expert who is very familiar with the 4wd trucks with a transfer case and ADD with a high lo electric switch on the dash. I have the FSM but would be willing to pay for help here is someone could help me with diagnostic to find the problem more quickly. Here is the info:
2000 V8 4wd SR5
4wd always worked but gave me a lot of trouble in the past. When turning the car on the 4wd lights on the dash and button would flash even though the car was parked in 2wd. I would have to press the button to engage and then disengage 4wd(one to five times) to make the flashing lights go away.
Sometimes I would engage 4wd and would hear the clunk and could feel the resistance of it engaged while turning but yet it never fully seated on the position switches so the lights on the dash would be blinking. Sometimes it would not engage mechanically either and the lights on the dash would again be blinking. Always pressing the 4 hi button a few times would eventually get it fully engaged and on the sensors so the light would be on solid, or disengaged and completely off.Occasionally had a Vacuum code Check engine light that became more frequent over the years, think it could be gas cap as its rusty and I smell gas right there but could be other lose lines as i did once have a bad engine fire from a punctured fuel hose(vacuum lines and wiring on front ADD could be suspect)For some strange reason I was under the impression that pressing the button(maybe cause the manual shifters) the transfer case engages first and when that position reads engaged then the front ADD actuates. I could be completely wrong though. Anyways now with someone pressing the 4 hi button in park or neutral and me under the truck the transfer case and ADD make no audible sounds over the engine running. If the button is being pushed, blinking, or just off the drive shaft that inputs to the front differential always spins freely with all wheels on the ground so both the add and transfer case are not activating anymore.Thanks for the help in diagnosing the issue.
Submitted: 9 months ago.
Category: Toyota
Expert:  Pete replied 9 months ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

I have seen issues with the transfer case actuator cause this fault here needing replaced.When the transfer case actuator is engaged it signals the ADD to engage and the actuator on the transfer case is the most common cause.It can intermittently act up at first in some cases then fail all together.I would have the fault codes checked/read out with a diagnostic scan tool that will plug in and read all computers in your model here to see what code are set in each computer.Once this has been done any codes set need diagnosed to locate and repair this issue and will help pinpoint if the actuator on the transfer case needs replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,a rating of 4 or 5 is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 9 months ago.
Thanks Pete, the transfer case was also my first thought since both add and tranfercase stopped working at once. I do not have a scan tool and am looking for specific advice to confirm the issue. I have a multimeter and can check if the wiring is sending the correct signals, I just need direction on what to measure, or what to listen for, or if I should take the actuator assembly off and apply 12v or inspect it some other way for function.
Expert:  Pete replied 9 months ago.

Unfortunately I do not show a manual test procedure on this here myself as this usually requires a scan tool to help test this and check codes.Below is the diagrams though on this model that may help in diagnosing this issue here.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.A rating of 4 or 5 is appreciated

Thanks Pete

Customer: replied 9 months ago.
Pete I already have the FSM. I was paying for this to help me save time and I asked for an expert on Toyota 4wd system. I can certainly figure out if it mechanical or electrical on my own but I would not give a satisfied rating for spending my time doing so. Do you have a way of ending this or differing to someone with better experience so I don't have to give a bad rating?
Expert:  Pete replied 9 months ago.

I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.

Thanks Pete

Expert:  Toyota Service replied 9 months ago.

Hello. Different expert here. Experience in this issue (4WD light blinking on start up) usually indicates that the Automatic Disconnect Device ("ADD") on the front axle is not functioning properly. This can be a host of things. Most common is corrosion buildup in the ADD wire connector. Also, quite often, we find, when we see this issue in the shop, that the ADD unit is sticking internally (ie bent from an impact to the ADD unit), the internal contacts inside the ADD unit are worn out/misaligned/damaged, etc, or there is a wiring issue. Normally, when the key is turned on, the 4WD system checks the position of the contacts in the ADD and the transfer case motor. Operation of 4WD is as follows: select 4WD. Power is sent to the ADD unit, where it moves into place. The contacts in the ADD unit close, which then sends power to the transfer case motor, causing it to move. WHen the contacts int he transfer case motor close (as in 4 HI for example, the system is satisfied and the 4 WD light comes on. If the contacts are sticking, on start up, (like the ADD is in 4WD but the selector is in 2WD), you get the flashing light. Most likely, you need ot replace the front axle ADD unit if there are not wiring connection issues. Hopefully this will assist you in you diagnosis of the system. If you need any assistance, please feel free to respond. Thanks

Customer: replied 9 months ago.
OK thanks. I'm going to stick a multimeter to each contact and then a ground on the front add and have someone press the button while I looking for voltage. If I don't find any voltage I'll look for the transfer case next. How sure are you that the add goes first? I was thinking it was the other way around because on manual shift version the shifter is attached to the transfer case and after that shifts it sends the signal to the ADD. Of course I don't have the manual shift I have the 4hi 4 lo push button.
Expert:  Toyota Service replied 9 months ago.

ADD issues are the most likely suspect. it is low on the front axle; where it can receive damage from debris on the highway, pot holes, curbs, etc. Plus a faulty wire connector can and will allow road water to enter and corrode the contacts. We remove the front axle assembly when we change the frames on these units (a recall). Quite often we find issues with the ADD (wires/bent, etc). The ADD gets its signal first because it has to engage Before the transfer case engages, or the transfer will see a disconnected front axle. This would not be good for the transfer unit, sending power to the front shaft and it is not delivering power to the wheels.

Expert:  Toyota Service replied 9 months ago.

Here is what we do (the first thing) when a customer has a blinking 4WD light on start up: We start the vehicle. and, whilst the light is blinking, a mechanic taps the ADD unit with a mallet. If the light stops blinking, the ADD is the problem.

A positive rating would be greatly appreciated for my assistance. If you have any other questions. please respond.

Expert:  Toyota Service replied 9 months ago.

Saves a ton of wire diagnosis time; the tapping trick.

Customer: replied 9 months ago.
Hello,Thanks for your confidence with directing me to the ADD as being the first item to engage. It must be electrical because it came back to life for a day after not working for 2 weeks. Now when i start the vehicle 4wd is disengaged, the 4wd light starts blinking from starting the vehicle, pressing the 4wdhi in the light stays solid for 1 or two seconds there is no engagment and after the 2 seconds the light continues to blink. So knowing that its electrical going to or in the ADD i will eventually get to diagnosing it for wiring leading to it or terminals at it. If you have any quick insights as to something that commonly corrodes or breaks it would be appreciated but not necessary. Ill start tinkering with that plastic cap and the wiring harness to make sure its getting a signal. I'll keep this open in case i have any more questions and I can tip accordingly if it drags on.
Expert:  Toyota Service replied 9 months ago.

No worries; glad to help.