4x4 engagement problem

Hi all,

let me start by saying I’ve read as much as I can already here and am still at a loss, oh and my electrical skillset is pretty weak compared to a lot of posters out there.

recently 4hi and lo quit working, and the 4lo light is constantly flashing. This has all happened after:

1) I replaced the PRNDL switch. What a nightmare. Frozen on, and 2 male pins broke off inside the amp connector. Had to splice on a new harness. Well, everything was cherry after for a few weeks, then I started getting really hard shifting and threw codes for shift solenoids A and B. Couldn’t figure out why, took it to a shop.

2) shop replaced internal transmission harness, solenoid codes went away and shifting returned to normal. Almost immediately after tho, the 4lo flashing light commenced. Took it back to shop. They claim I need a new t-case actuator motor. Unlikely, I thought, as that would be a wild coincidence.

So I brought it back home to try and figure out wtf. I can confirm the front ADD is not engaged; the wheels and front shaft spin freely and independently. The front shaft does not lock into 4x4 no matter where I spin the switch; it always blinks 4lo. So I start to think maybe it is the actuator. But I pulled it out and it’s super clean inside. I also bench tested it and the motor spins. So it must not be getting the proper command from the ecu or something is out of phase.

any thoughts? Obviously the shop is saying it is unrelated to their work

ive tried to read the diagnostic for the 4x4 system but my ecu pin outs don’t look like anything in the diagram.

 

Did you take the actuator apart and inspect the contacts?
There's alot of info in this thread about how to test the T-Case actuator.

 

I tell you Toyota really F-ckd us good with this actuator nonsense! Dealerships know about it too and still charge big bucks for that electrical junk! Similar issue to you. Read pages and pages on here, these guys know their stuff but I feel each Tacoma has their own set of issues...here's mine

1. truck engaged 4-HI with 4-hi and 4-lo light blink then would not get out of 4-hi

2. pulled front diff actuator (replaced with new/tested motor and it works), manually position sleeve on front axle to free (2wd) position. not sure if that is the right terminology but on stands spin a tire and only that tire spins. move sleeve opposite direction and spin tire they both spin.

3. check 4wd fuse (good) reset 4wd ECU and disconnect battery terminals = 4-hi light still blinks

4. took for a test drive around the house and feels like its 2wd but when trying to make a turn I could feel the wheels binding so that sh*t just got me frustrated all over again!

Questions I gotta get answered?
1. Could my tcase be talking to front diff and sending a signal to go back to 4wd (meaning tcase actuator faulty?) who knows!

One thing to note, when testing to see if new ADD would work I took new ADD and plugged into connection then went to 4wd switch....no movement so perhaps my switch is bad

#tacomaproblems

 

yes they’re super clean. Like I said bench tested the motor and she spins. Not sure about the position limit switches tho, how to test? Problem must be them, clocking on the t-case motor (though I’ve never removed it) or some problem between switch and t-case motor. Is the harness to the t-case a branch from the main transmission and prndl harness? Since this came about right after those issues were fixed, I’m forced to think they’re related

 

Testing the actuator is explained quite well in posts 16 and 19 of the thread I posted above.
There's also alot of info links about the 4wd system in this thread.
And I've included the Toyota guides on the 4wd system.

 

Yes, the PRNDL is part of the 4WD system
The Neutral is really the only thing used, it supplies B+ (power) when it Neutral.
This allows you to shift to 4LO.

If you can’t shift into 4Hi, I would not think this is a problem.
Unless there is a constant ground on that pin or the 4WD ECU?
And then I don’t know what it would do?

 

If I ever butt into this issue, I think I'll do the FJ transfer case swap. Electronic 4x4 is my biggest gripe with the Taco's design.

 

I swear after I get it driveable again I'm gonna do the FJ tcase swap

 

Problems with 4wd systems are not exclusive to Toyota, all vehicles with electromechanical 4wd have issues to some extent, Toyota only differs in the fact that there's no diagnostics built into the system so everything has to be tested manually.
The big thing with electronic 4wd systems is they need to be engaged regularly to keep things in working order even if you don't need it otherwise your more likely to have issues when the time comes and you do need it.

 

Didn't say it was Toyota exclusive. When I was considering a GM or Chevy I wasn't even looking at the push button models.

 

I noticed the last few years my 4WD would engage with a thud, then a few weeks ago it stopped engaging. I feel mine wasn't used enough was the cause, so I'm just going to leave it as a 2WD as much as I wish it had 4WD.

 

thanks for that reply; I’ll try and wrap my brain around it…

I should note that in addition to the 4x4 issue, a P0500 code appeared shortly after bringing it home from the shop. My speedo works fine. Can’t believe they’re related but did want to put it out there.

also… while trying to diagnose today, I clocked the contacts in the t-case motor to 4hi position to see what would happen. What do you know, the actuator engaged the front shaft. Now the ecu still thought it to be in 2wd, and so therefore the ADD did too (the front diff did not lock), and the same lights continued blinking, but I do know the actuator can engage. I moved it back to the 2hi position after and all is well again, and by that I mean I still have no 4wd, tcase not engaging front driveshaft, and 4lo constantly blinking. Wtf

 

I don’t know if that will prevent it from going into 4WD.
I do know that you can not switch to 4WD at or above 62 mph.
If the ECM doesn’t detect the speed, maybe it will not let you switch to 4WD?
I don’t know, I haven’t ever seen anyone with both these problems at once.


Here is a link @Dm93 posted to the 0500 code.
https://www.tacomaworld.com/threads/speed-sensor-code-po500.731927/#post-26072008

 

I would check to see if you are getting voltage at F12 pin 23 with the transmission in neutral. If your mechanic was sniffing around and replaced that sensor there's a chance the 4wd ECU is not seeing the trans in neutral. I'm not sure if that would cause the 4lo light to flash, but this is where I'd start since it was the last thing to be touched on the truck, then proceed onto the further troubleshooting @Dm93 recommended.

 

The failure modes are all the same, unfortunately there are many components to fail thus a variety of failure modes and the symptoms of each are different. I assure you that you haven't broken it in a different manner than others have before.

 

Since he is an Automatic Transmission, wouldn’t it be the N Pin?
I thought the MNT was for manual Transmission?

 

I don't have the OE diagram handy but looking at the Mitchell diagram you appear to be correct.

 

Shoot you're right, I had a Friday brain fart thanks for checking! Yes check the 'N' pin on pin 22 of F12. I would expect ~12VDC with the transmission in neutral.

 

I have 12v at pin22 in neutral and 0v in park so all good there.
Is it possible that if the ADD is bad it will keep the tcase actuator from engaging? I assumed tcase actuator is the problem because the front shaft is not engaging, but wondering if a bad ADD would send back a signal telling the tcase not to engage?

 

I have an update here, in fact I’ll even call it a temporary “fix”, but I have no idea how/why/what is happening.

so in my quest to restore 4x4, I pulled the TC actuator and ADD. Both spotless inside. Both motors work when power is applied to the harness pins. Still have the blinking 4lo light and no engagement. Tested limit switches; all good. Even ordered a new TC actuator and popped it in to verify. Same result. As noted before, I have an intermittent P0500 code that appeared at the same time. So I plugged in tech stream to see if I could learn more. Well as soon as I started the truck, no blinking 4lo. No lights at all. Switch it to 4hi, went right in. 4lo, went right in. So I go on a test drive. Half an hour of engaging and disengaging… worked like a charm. So I decide to unplug tech stream and reattach my head unit to the OBDII (I have an iDatalink Maestro connected to a Pioneer AVH4200) to see what happens. Immediately the flashing 4lo light returned and truck would not disengage from 4wd. Pop out the Maestro and plug tech steam in again - selector works perfectly. Wtf? Repeated this dozens of times, same result. So then I decide to leave the Xhorse mini VCI plugged in to the OBDII, but UNPLUG the USB port from my tech stream computer. Still works??? How is that? Again, repeated dozens of times. As long as the Xhorse VCI is plugged in to the OBDII, whether or not the other end is connected to anything, the 4wd system never skips a beat.

how can this be possible?