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Hi there, I have read quite a bit in regard to the Tundra electrical issues around the 4WD functionality. I recently have joined this club and the best I can do is articulate what I know is going on with my truck and hopefully someone can put it all together with a solution. Here we go:

2007 Tundra 4.7ltr, SR5 TRD 4WD 145k miles

  • a couple of months ago my brakes felt as though the ABS was engaging over very small bumps and very low speeds _5-10 MPH. This has continued until recently when the 4wd stopped engaging electronically.
  • During the time when the ABS was acting funny, and hoeslty kinda scary when at high speeds and you hit the brakes, all 4WD functionality worked.
  • I recently pulled my HVAC guy out of my front ditch using 4wd just fine. the day after, in normal 2wd I was getting some vibration from the front, and usually when this happens I just toggle back and forth from 4hi to 2wd a couple of times until it finds a good position and the wheel vibration stops.
  • Now during normal operation my 4 hi light flashes continuously while the truck is on and the switch does nothing when flipped into 4hi. Special note here that normally I could hear a high pitched something engage in the dash when switching to 4hi....This engaging noise has now stopped as well, like it was behind the air controls or something?
  • I have finally figured out that the truck will engage into 4 hi, if I switch to 4 hi then turn the truck off and restart in 4 hi.
  • Vice versa the only way to get it out is to switch to 2wd while on, then turn off and restart then the truck will go back into 2WD
  • I can tell there has been a repair on the front drivers side Speed sensor wire harness and when I went to take a peek it corroded in my hands, I removed the sensor and ordered another harness that should be here this week. regardless with the complete sensor removed the 4wd is still acting the same.
  • Is there a relationship to the ABS speed sensor and the 4 WD engagement process?
That is all I know at this point, again several issues I have read about but none seem to fit the bill as to what is going on, I think it is a good thing that it is engaging when I restart the truck which leads me to believe more of an electrical issue. I appreciate the help folks! Matt
 

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An active ABS and hydraulics can sound like you are describing when they are kicking in. A bad wheel sensor could definitely cause issues where ABS and VSC are involved in your 4wd.
Because you can engage it when restarting is probably because you are stopped and there is no disagreement in wheel speed.
Sounds like you discovered at least the obvious problem which should be causing at least one ABS code. Get that harness replaced and reset everything and see where that gets you before beating your head against the wall.
Sometimes in troubleshooting we are gifted with obvious things like damaged wiring.
 

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silly question: How do I reset everything? disconnect batt?
You can disconnect the battery to clear your normal codes but if that doesn't work you may need an OBDii tool that can access and the ABS like our iCarsoft TYT II tool.
Assuming you actually fixed the problem before trying to clear the codes. It has more diagnostic power than your basic generic obdii tool but is much less expensive than a full professional tool.
A good OBDii tool can be invaluable and they usually pay for themselves very quickly if you work on your own vehicles. I use the TYTII myself over my Toyota Techstream computer for some of the more simple things.
 
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