4wd System Operation & Help Thread

If you selected 4H when you took these readings it looks like the 4wd switch on the transfer case actuator is not opening it should read 0V in 4H position, can you hear the transfer actuator moving when selecting 4H?. Also select 4H with the front wheels jacked up and turn the wheel to make sure front actuator can engage.

 

It was in 2wd when I took those readings, and I can hear T-case engage but the front diff doesn’t do anything, both actuators are new and bench tested so I’m confident they should work

 

Wow yea iridium plugs shouldn't wear that fast.

 

Ah just seen that at the top of your pad. I see TL1 is reading 7.2v that should be zero, did you open the transfer case actuator, looks like the timing is off. TL1 should be 0V in 2H and TL2 and TL3 12v like you have.

 

Yea we are suspecting bad grounds because of that and also having 1.7v on the 4wd ECU ground pin.

 

I wouldn’t be surprised if it is off timing, but having voltage at the grounds still doesn’t make any sense to me, I’ve checked around my bell housing and nothing got pinched, while the valve covers were off I had room to feel behind the head and the grounds are very solid and not pinched, none of the wires leading back or to the actuator are

 

Check between pins 5 and 6 on the actuator first to see if you have continuity, if you do then the timing is off, fix that first before anything. A false ground could be coming up because of the way the actuator timing is set.

 

If the actuator was in that position we should see 0v on TL2.
The 7v on TL1 and all others being correct suggests a corroded wire, bad ground to pin 4 of the actuator, or corrosion/bad contacts in the actuator.

 

Relative Quick Question regarding all this great info. 05 Taco, brand new actuator installed due to not going into 4Lo. 4Lo only is inop. Still not working after installed. I did not diagnose what so ever. Now this is coming to my shop for me to work on. Any quick hints on where to look as far as back probing and voltages and what not? Any info would be greatly appreciated

 

I would first want to see if it beeps when trying to go into 4 Low at a stop, if it does that would tell me it is either not getting a clutch (MT) or neutral (AT) signal or is seeing a speed signal when it shouldn't.

If it doesn't beep but the lights flash I would be focused on TL3 and the L4 Pos Switch, and TL2 signals.

If nothing happens when the switch is turned to low (no flashing lights or beeping) then you need to check the signals from the selector switch.

 

I should have been a little more descriptive. It does beep and flash, just never engages. I have verified that the transfer case itself can go into 4 low and is not an internal problem, Also the truck is an Automatic transmission

 

Transmission must be in neutral and vehicle speed below 3 mph to go in and out of 4 low, if you are meeting this criteria and it's still beeping you need to check the N signal pin (A22 Blue/White) for 12v with the transmission in neutral.

 

Will do and I will keep you posted on the results. Thanks

 

Hey Y'all,

Thanks for this in-depth thread. I'm dealing with 4wd issues on a first gen, selector switch seems good, and I think I can hear the actuator move but the wheels never get power and the 4wd light never flashes or anything and no beeping. It's a bit chilly here in WY, so hoping I can diagnose things before lifting it up and start pulling parts. I'm wondering if the limit switch voltages in the OP would be the same for 1st gen or if there is similar info out there that you all know of?

Based on the shift sequence described in the OP I’m thinking limit switches or 4wd Detection Switch on the Transfer Case Actuator, but this is all pretty new to me. Curious if y'all have thoughts.

Cheers!

 

I'm not too sure how the 1st gen systems work but I can do some looking in the service info tonight and see what I can figure out.
Do you have the push button shift or mechanical shift?

 

They work the same way the second gens do as far as the front actuator goes.

If it's a J-shift, the 4wd switch activates the ADD ECU to shift the ADD from unlocked to locked when the mechanical lever moves the shift rod and actuates the 4wd switch in the transfer case, and vice versa when shifted manually back to 2HI.

If it's a pushbutton shift, the "pushbutton" is the same as the 2nd gen selector switch. When going to 4LO, it's still a mechanical shift, so the main difference is the transfer case actuator only has 2 limit switches vs. 3 of the 2nd gens.

 

It's push button.

 

Well, not sure how or why but after getting new tires on today 4wd is good to go. *face palm*
Perhaps something was just seized up and got shook loose, but obviously don't want that to happen in the back country. Any thoughts or preventative actions?

 

Check the vent hoses on the actuators and engage/disengage the 4wd system more often is about all the preventative maintenace you can do.

 

Sounds good! Thanks for your attention!