A Solution to 4WD Light Blinking Issue

Hey Folks, I'm new here, thought I would share my experience with this issue in hopes it might help someone. Forgive me if this has already been solved, but I spent hours and hours scouring the internet, and while I learned a ton and found some possible solutions, none of them worked for me. Most of the resources provided below are for early 2nd gen's but they were still applicable to my 2013. This is long, but worth the read if you're having this issue and don't want to waste money at the dealership replacing expensive parts unnecessarily.

My issue, as described by many others, was that my 4WD dash light would continue to blink after switching from 2hi to 4hi and then even after switching back to 2hi. I would have to turn key off and back on in order to go back to 2hi. Rocking back/forward did not help. 4lo would not engage either, presumably because it needs to recognize its in 4hi first.

Troubleshooting procedure:

1st, I jacked it up and confirmed it was in fact in 4hi and front diff was locked after switching to 4hi, it just seemed the computer was not recognizing this and therefore not making the dash light solid.

Next, I opened up the front diff ADD actuator, the most common culprit (https://www.tacomaworld.com/threads/4wd-actuator-fix.478818/). Everything looked normal. "Vacuum" hose fine. I soldered the little motor joints and cleaned/re-greased for good measure and reinstalled. Didn't help. Then I opened the transfer case actuator: https://www.youtube.com/watch?v=TmuEVv1neVQ Also clean.

Then I checked resistances and connections (probably should have done this first).
-20A 4WD fuse (low, behind dash, left of steering wheel) looked fine.
-ADD: https://www.tacomaworld.com/threads/tacoma-add-delete-wiring-figured-out.464595/ or https://forum.ih8mud.com/threads/4x4-troubleshooting-4hi-light-blinks-4lo-will-not-engage.682716/ Checked out.
-Transfer Case: https://www.dropbox.com/s/si8tcvwlptre8ct/4x4 troubleshoot guide.pdf Checked out.
-4WD switch: same file as above - The resistances listed aren't completely accurate given the actual design of the switch. If you want a better explanation let me know, but nonetheless, this was not the issue.

Finally, I checked ECU voltages (https://www.tacomaworld.com/threads/4wd-ecu-location.495036/) Remove the glove compartment and the plastic panel just above it (single 10mm hex bolt, center). 4WD ECU is high up to the right behind remaining panel. Use a small phillips head to remove the 2 mounting screws. The higher one is a b!tch. Reference this guide: https://www.dropbox.com/s/2kkxl5mc1rp3pze/TACOMA 4WD DIAG.pdf Keep the two plugs in the ecu and connect your black voltmeter lead to vehicle ground. For the Red voltmeter lead I had to use a single copper strand and carefully push it into the small slots on the plugs where the wires enter. There's probably a more sophisticated way to do this but I'm an amateur. Everything checked out for 2hi and 4hi voltages per the guide, except for slot number 26, connector B, (grn/blck wire) which is the signal coming from the ADD (go figure). In 4hi it read ~12V when it should've read 0V (ground)...

Okay, so at this point I still don't know exactly what the problem is, but I've narrowed it down to one section of the 4WD circuit: between the ADD and 4WD ECU. I snipped the grn/blac wire, switched to 4hi, and then manually fed the ECU 0 Volts via port #26. Dash light goes solid. Holy $@%*. Switched back to 2hi, removed 0V signal. Light cuts off (it does not need 12V to cut off). For some reason, the ECU had not been receiving the signal from the ADD that the front diff lock was engaged, even though the ADD works fine. So, instead of investigating further and possibly creating more problems, I decided to just install a simple on/off switch that feeds the ground signal to the 4WD ECU. All I have to do is flip this extra switch on after rotating from 2hi to 4hi, and off after rotating back to 2hi. Note: sometimes I still have to rock back or forward a bit to get the light go solid. 4lo and RR diff lock work fine now too.

It's not the ideal solution, but it's A solution and has been reliable so far. Sorry, I already put it all back together so I don't have pictures of the wiring (plus I don't want everyone to see my sloppy wiring/soldering) I hope this all makes sense and helps someone. Feel free to HMU for questions or further clarification. Thanks for reading.

 

Nice. Yes that indicator is used by the 4x4 ECU as well as the PCM to determine if the truck has engaged 4wd or not. I did the same thing years ago, to get my atrac to work on mine, since it never recognized I was in 4x4

 

This helped me immensely, thank you!

 

I think this might be my problem. I don't seem to be getting continuity on the green black wire, but everything else checks out. I actually replaced the ADD as its pretty cheap nowadays.