4wd System Operation & Help Thread

^^^^ This + 1

I have come across more problems caused by bad grounds on old cars of mine that make "Christine" look like the Easter Bunny. The one I remember most is turning is on the headlights making the brake lights come on bright on one side and dim on the other: Fix: bad ground. five different wires stacked and corroded under a rusty bolt on the body in the trunk.

 

Thanks for the tip. Just checked

I have 12 Volts at the switch across the terminals and with switch depressed meter does beep(continuity).

Still searching.

If I understand correctly the 4wd switch signal must go to zero before the add gets triggered to move.

 

Interesting, try jumping the terminals with a paper clip or suitable tool that won't spread the pins of the connector and recheck the voltage on Pin 22 (Red/Blue) at the 4wd ECU, it should read 0v if the circuit is intact.
Has the transfer case actuator been off before, if it has it could be out of time.

Correct, it has to see the 4wd detection switch in 4wd (0v) before it will lock the ADD.

 

With the paper clip in the terminals pin 22 indeed goes to zero volts. And I get a beeping sound from the front diff add. I did just replace the add with a unit from Napa as I originally thought that was my problem.

I ordered a new 4wd sensor switch to try. Will report back.

the tc actuator is the original and hasn’t been messed with.

 

Difinitely sounds like either the sensor is having a problem or something in the Transfer Case Actuator isn't moving the shift rod quite far enough to push the 4wd switch.

 

Good news. New 4wd sensor did the trick. Now have O v at pin 22 with the switch at 4wd.

now the truck clearly goes into 4wd but the light on dash keeps flashing. The front add actuator is still beeping in 4wd. To get back into 2 wd you have to turn the truck off and while off turn switch to 2wd. And upon restarting you are back in 2wd

when rechecking voltages dl1, dl2, add all are at 0v while in 4 wd. And are at spec while in 2 wd.

so it seems like the sensing function of the front add is faulty.

 

Sure sounds like you have a faulty ADD, to verify the wire isn't shorted to ground unplug the ADD and verify DL1 goes to 12v.
Did you keep your old ADD, I bet there was nothing wrong with it.

 

Just want to say this is an awesome thread. I have been following it for several days because I knew in my gut the OP and the owner were likley going to figure it out: (both the probable culprit and the fix) thus saving the owner HUGE money, frustration, and heartbreak, in both dealer diagnostics and new parts replacements and have the system still acting up as horrendous winter weather sets in for good across 90% of the U.S. Well done.

 

Well we're one step closer anyway, but we'll get there. I like testing and knowing a part is bad instead of trying a new part and hoping it fixes it, especially with the cruddy parts we get now. So many parts are bad out of the box, just replacing parts without knowing they are bad just ends up "building in" more problems than you started with.

 

I had the same issue. My front ADD was full of water. Ended up finding a hole worn in vent tube. There’s a clip that hold another line on and every Tacoma I have looked at all are rotated back and they rub a hole in the vent tube so I would double check that.

 

Thanks for posting that, what is the location of that clamp?

 

If you follow the small short rubber vent hose off the ADD to where it goes into the hard line, then there’s a short hard line and then it goes back to rubber after the short hard line. Follow that 2nd hose that goes up to the top of the engine bay. It’s not too far up from where it comes out of the hard line. Some Tacomas have about 1/2” clearance and some are rubbing. I have a 2012 and I’ve looked at em all the way up to a 21 and that clip is in the same orientation. You can try rotating the clip or just bend the hard vent line back a bit to clear.

 

Interesting, I'll have to take a look at mine.

 

I would if I were you. My ADD was acting up so I pulled it and soldered the connections and cleaned it up an siliconed it all back because there was a little water in it. Reinstalled and was working fine for about a month then pulled it again and it was full of water. I started trying to figure out where the water got in and found that hole. I took that pic and posted it on my instagram account. Ended up having to buy a new ADD and replaced the vent tube and extended it up by my brake booster.

 

I check my hoses everytime I have it on the rack to change oil or do other things but I didn't know about the clamp, if I can find it I'll get a better picture and post it at the top of the thread.

 

O

ok I’ll look tomorrow and see what hose that clips on. You can’t miss it if you follow the vent tube. Maybe follow it down from top of the engine might be easier but you’ll see it.

 

I'm gona pull it in and take a look if we aren't too busy at the shop tomorrow.

 

Holy moly! Hey fellas, im brand new here, i just had to create an account! i've been chasing a problem with my truck for the last few months, evap codes, 4wd light flashing, no cruise, trac off, etc. Then i found this whole thread, specifically the posts concerning the bad grounds. Let me explain a bit:

So this all started a few months ago, my 4wd light would flash intermittenly, but a simple off,on again and it would work good as new. (Im not normally one to leave thing but im on a farm and its a busy time of year). Then one day it completely up and quites and wont do anything, just flashes. So some time later, i'm fixing an exhaust leak, i cut the connection apart, put in my exhaust seal, bolt it back together and NOW i'm getting a check engine light with evap codes, abunch for the Secondary air injection system codes, no cruise, 4wd still flashing, trac off etc. So on goes new evap cannister, some codes go but not all. Then i put on a Hewitt Tech bypass kit for the air system, which after the neg batt terminal off reset, cleared all those codes, so the ONLY thing left now was the 4wd light flashing. (not sure if the cruise was back or not, it was a blizzard yesterday so didnt use it) which brings us back full circle a bit. So this morning, after said blizzard, i just in the go over and milk the cows and i got check engine light, trac off, 4wd still flashing etc. I almost lost it. Throw the ol' code reader on it and i got P043E, P043F, P2401, P2402, P2419; the same codes as the ones back at post 236! So now i'm thinking i've got a bad ground someplace. Sorry to share my life story on this but i'm super excited to find this! I'm going out to get my multimeter and the code reader. I'll let you know how it progresses!

 

Code reader plugged in, 4wd WORKS! Eng light is still on, but i imagine that stuff will go away once the evap system has had time to cycle again. didnt try cruise but i imagine it'll be working too!

 

Good evening boys, I am calling on all the witch doctors in this forum for their expertise because my brain is short perculating over here.

Start from the beginning here - Truck backed in on drive way incline. My dumbass was testing everything electrical on the truck after another event and switched 4wd Cab switch from 2H -> 4H While in “Park”. Did its normal 4H light flash followed by instant 4H light plus 4Lo light. Figured ahh fuck I fucked up. Let’s trouble shoot. Pulled forward, reversed trying to get it to shift it. Nothing. Turned truck off, put it back in 2H. Turned back on, lights still flashing. Realized -> I fucked up. So since then, truck has had both dash lights flashing.

Trouble shoot - Tried pulling truck off the driveway and going forward reverse while shifting Cab switch back and forth. Nothing still.
Jacked up front of truck - Front wheels spin opposite of each other. Front drive shaft rotates when pulling forward. So mechanically, looks and feels like it’s in 4H.

The great Cornholios in this thread preached back probing, so that’s what your boy did. This is what I got and I need some help diagnosing these maths.



So to sum up - Mechanically the truck is in 4H I think. But the maths above are saying the front diff is unlocked and the 4Wd position switch is saying it’s in 2H. The dash lights constantly flash so that’s telling me the ECU has thrown in the towel until I fix it. The limit switches also look like they’re out of sync. But my understanding is that the front diff switch wont active the fork until the 4Wd position switch goes to 0v. So is the truck got a half chub in 4H and isn’t fully activated which explains why everything moves like it is?

My first born child as a gift to whoever helps me fix this fat whore of a truck.

Thanks.