4wd System Operation & Help Thread

Well we need to check circuit integrity to be sure but it doesn't appear to have moved since there is no change in the limit switch voltages.

To check circuit integrity of the limit switches you would need to ground DL2 (Pin 5 (Pink/Blue)) and ADD (Pin 3 (Light Green/Black)) at the ADD Actuator and verify that they go to 0v at the 4wd ECU and the DL1 goes to 12v with the ADD Actuator unplugged.

 

I took quick look under and the hose is good, (no splits or holes) but did show some rubbing in the area you referenced. I gently nudged it away little bit and slipped a small length of the black-plastic split wiring loom around the hose in that area.

Follow up: The actuators snapped to and engaged quickly this morning when I tried them: no blinking or drama like yesterday. I had the drivers' door open and the actuators worked quickly and the front diff gave it's nice/loud metallic ring/clunk as it engaged.

Guess they are just old and a little cranky now.... (kinda like the owner. )

 

4Hi not engaging. No sound of actuators moving on 2Hi->4Hi. Relays clicking in dash. 4wd indicator blinks.

After backprobing, state remains unchanged in 2Hi vs 4Hi except A8 and A15 which show expected value for 4Hi. Following the state flow chart, the actuator motors are going to ~10.5v, not the ~12 expected/seen elsewhere. This and other readings seem to indicate fault with actuator motor (at a minimum) as well.

Based on these test results and my understanding, R&R of the tcase actuator assy are in order, pending a bench test. Can someone with a fuller understanding please confirm/berate me?

Thanks.

Static backprobe results:


State change results (2Hi reading -> 4Hi reading during ECU logic operation))

 

Kind of suggests the Transfer Case Actuator is stuck, do you have a DC current clamp that you can check the current on the actuator wires with?

Could also give the actuator a few light taps while someone operates the switch and see if it takes off.

 

No clamp, tapping in place didn't do the business- tried that even before probing

 

I mean if you have the right backprobes you could backprobe the motor wires at the Transfer Case Actuator and make sure power is getting there.

 

I'll give it a shot, I did follow the wiring as best I could and didn't see indication of damage. Would a continuity check between the ECU end and the actuator end work or are there devices in the way?

 

You could do that but I'm generally not a big fan of continuity testing, it will tell you weather or not the circuit is "intact" but won't tell you if it can carry a load (current).

 

Yeah, I'll toss a 9v inline and see what I get out the other end. I'm not particularly suspicious of the wiring, but if I'm doing this level of testing already it's not much more of a hassle to check all the boxes.

 

I see a p/n 36410-34015 Transfer Case Motor from Toyota. Catalog photo shows just the metallic assembly without the black plastic cover with timing traces etc. I see some descriptions for same P/N as "Transfer Case Assembly".

Can someone confirm that 36410-34015 is in fact the entire assembly?

 

Thank you!! A lot of great information in this post.. I need to read it again and recheck my notes.
Thanks once again..

 

Hey everyone, I’m running into a bizarre 4WD issue and could really use some insight.

It started with the dreaded flashing 4x4 light. Confirmed I was in 2H and measured around 7V on all pins that should be getting 12V. I suspected a bad ECU, so I grabbed two spare 4WD ECUs from the junkyard.

Here’s what happened:

• Plugged in the first spare ECU, turned the ignition on, and got continuous clicking from the ECU, lights still flashing.
  
  
• Turned it off, then back on — this time just one click at ignition and the lights went off. Eureka! It then actually shifted into 4H!
  
  
• Moments later, both the 4H and 4L lights started flashing again.
  
  
• Now the ECU no longer clicks on startup, and now I’m stuck in 4H.
  

Both backup ECUs are now acting dead in the same way after testing this process. EE Ground behind the motor checks out fine. Still getting ~7V from both the transfer case position signals and the ADD. Seems like an electrical issue rather than mechanical, but I’m stumped.

The bigger concern — I have a trip this weekend, I can’t easily source more ECUs, and I’m worried I’m frying them because the root issue hasn’t been found. Any insight or direction you could provide is greatly appreciated.

 

I replied to your thread.
https://www.tacomaworld.com/threads...wiring-need-help-with-12v-feed-source.858824/