4wd Not Engaging - 2nd Gen TRD - Out of Ideas

Hey there. New here so excuse any lack of etiquette.

Recently discovered the 4wd in my 08 TRD Sport won’t engage. Just getting the blinking light on the dash. I trolled the forums and decided to replace my 4wd actuator on the front diff. No change. Checked all of the electronics I could find/think of (dash switch, harness at actuator). No issues. Tried tapping on the t-case actuator. Nothing.

I’m at a bit of a loss and am trying to avoid a multi-thousand dollar trip to the shop. My next thought is to go through and re-test the electronics. I tried the switch when I had the actuator out, and it moved the forks just fine. So any input on where there could be a disconnect?

While tapping I noticed the vacuum tube on the t-case actuator was on, but pretty loose. Could that be an issue?

Any sage advise from the legends of this forum would be much appreciated.

 

Have you gone through this thread?: https://www.tacomaworld.com/threads/4wd-system-operation-help-thread.742420/

@Dm93 is really good at diagnosing 4WD issues and put that thread together. After reading that thread, if you still have problems reach out to him.

 

This is amazing. Thank you for sharing!

 

Sometimes it's cheaper to let a pro look at it than continue to throw parts at it.

I'd take it out onto a dirt or gravel road, flip the 4X4 switch and drive it. It isn't unusual for a 4X4 that hasn't been used in 4X4 regularly to not want to engage. If you don't use it, you lose it The lubricants in the hubs and other parts dry out and sometimes just driving it in 4X4 will loosen things up enough to get things moving again. We had a Jeep Cherokee that my wife drove years ago that didn't get 4X4 engaged for about 6 months. I ended up having to take the hubs apart, clean out the old, dried grease, re-lube everything and reassemble. No parts needed. It worked perfectly.

Sometimes just driving it in 4X4 might solve the problem. But it might take a few hundred miles in 4X4.

 

I’m lost. What do you mean by “lubricants in the hubs”? They are sealed grease bearings.

 

Before you spend a lot of time...check the breather hose on the transfer case actuator. They're known to come off and allow water to get in.

 

Separate from the large torque-transmitting & locking moving parts - shafts, rods, locking collars, etc. -- a significant fraction of problems comes from oxide corrosion build-up on the electrical contacts: the sliding metal "wiper arm" on the copper circuit board traces inside the actuators.

If the 4x4 functions aren't touched for a long time, depending on environmental conditions eventually the corrosion on the moving electrical contacts inside the transfer case actuator can stop them from making electrical contact, leading to a flashing dash light & no 4x4 activation.

Part of "exercising 4x4 mode" is just regularly moving the electrical contacts so that they keep the oxide layer on the contacts/traces thin enough not to cause loss of electrical continuity.

 

I concur. However the wheel hubs aren’t affected by lack of 4WD use.

 

Go look at the vent tube that was 'loose' again. If the end is split, there's a good chance there's some water and corrosion in the transfer case actuator contacts and they may be a touch corroded. That is probably 95% of the failure mode for these 4WD systems (in my opinion).

 

You say you checked electronics.. what were your ohm values at each connection? Check 4wd output control and reference voltages from ecu? Verify continuity at all terminals and junction connections? You took an oscilloscope to all of the sensors?

Ill bet you my hourly rate for diagnosing electrical to tell you its an electrical issue. I will also tell you as a professional its never as easy as it seems and i doubt any non mechanic thst says they checked everything... especially when it comes to electrical.

 

FWIW: I exercise the system on my truck a couple of times per month in the driveway, and engage it on the road whenever it rains or snows for a mile or two. It engages fine, but if I do it 3-4 times in a row, the last cycle from 2H to 4H and back seems smoother, quieter and quicker than the last. The front fork makes less noise each time ("clunk") than first one: just sounds "better" both standing still and underway. I only cycle/engage 4L at home in the driveway. Again, better engagement and sound on the 3rd or 4th cycle and fork engagement each time than the first cycle. I don't trust it (4L) to switch back on the road away from home. Four years/40k miles of doing this since I got the truck and all good so far.

YMMV, but in my opinion, if you go for months or years without engaging the system, at least on a 2nd gen, you're asking for trouble.

 

I definitely have not tested everything. Just looking at the chart on this beast of a thread, I know I've missed a bunch of stuff. My next step is to go through that. If everything looks good, then it might be time to call in a pro.

 

I'll check this again. Is there any way to verify this/fix it without taking off the actuator? Or is it as easy as the front diff actuator to take off and put back on? I'd be fine having a shop do this if it's outside of my comfort zone, which is admittedly limited.

 

Yeah, I wish I would have known about this/been better about it in the past... But can't go back now. I'll definitely be diligent about this once I get it fixed

 

HOPEFULLy that loose vacuum tube didnt allow water to get in the actuator because it corrodes the insides over time. saw that recently w someone who put in FJ manual tcase

that line frayed off my actuator and a reattached it and luckily 4x4 works okay still

try parking in the grass before engaging the system, it likes the friction

 

If you go through all those steps & use every other bit of relevant info in that thread you'll probably be doing more & better than 85% of "pros" who look at the problem.