Intermittent 4WD...only works when COLD?

I've been having the dreaded blinking 4HI light/no engagement of 4wd, and finally replaced my front diff actuator, which brought back my 4WD. Great! But now I'm noticing that the front diff actuator only engages first thing in the morning, or after the truck has been parked for an hour or so. After driving for 20-30 minutes, the front diff actuator refuses to engage and I get the blinking 4Hi light again. The actuator on the transfer case works perfectly every time I turn the switch.

I'm suspecting that it's a wiring issue somewhere along the line, and was wondering if anybody had any insight into what this could possibly be? Engine heat messing with a wiring connection somewhere? Man, what I'd give for a stick shift and manual locking hubs...

 

I'd start with checking all of your connection points throughout the harness and go from there. That's super strange that it's only engages when its cold out, I'm sure that someone here will chime in that has a similar issue or something close. Best of luck!

 

Thanks, yes it is strange, and it seems to be more of a cold engine than outside temp. Once the truck has been running for a while, that's when it won't engage the front ADD actuator. I park it for an hour or so, and it will work upon startup and the following 10 minutes or so.

 

I've narrowed the problem down; the front diff actuator won't engage once the transmission gets up to temp. I've let the engine cool off, but the tranny is still warm, and the front actuator still won't engage. Leaving it overnight to let the tranny cool down totally eliminates the problem. The transfer case actuators work perfectly regardless, but something about a warm transmission...

 

I’m having the same issue. Engages when cold, does not when warm. Any suggestions?

 

I’d have guessed to change the fluid but I assume you did that when replaced the actuator.

 

I've been kicking this can down the road, but the previous owner had a repair done to the wiring that runs from the transfer case actuator up to the 4WD ECU, a rat had chewed the wires. Since the wiring runs along the top of the tranny and up behind the engine, I'm guessing that the repair 'works' when things are cold, but the heat from the tranny causes the metal wiring to expand and a connection is lost. There are three limit switches in the TC actuator, and one of those tells the 4wd ECU that the TC is in 4wd, which then sends a signal to the front actuator to engage. I'm guessing one of those limit switch wires is the affected wire and isn't getting the signal from the TC when everything's warmed up.

Let us know what you find out please!