Truck goes in & out of 4x4 on its own!!

[Garry Verheyden]

I have an 03 6spd 4x4 with the electronic shift 4x4. I was going down the freeway last week and noticed the 4x4 light on. The knob was still on 2wd though. I switched it to 4x4 then back to 2wd a couple of times, then it switched back to 2wd. I was driving again yesterday and the same thing happened, but this time it wouldn't come out of 4x4. This morning I took the rear driveshaft out, moved the truck a few feet, then I managed to get it back to 2wd.

Do you think this is a transfer case issue, or a t-case electric shifter issue, or an electronic problem. Has anyone else had this happen?? I sure don't want it to shift to 4 lo when I'm towing my 36ft 5th wheel on the freeway!!!

I checked the oil level and the ATF started running out of the top filler plug. Lots of oil in. I have noticed a whine coming from the rear end or t-case sometimes at freeway speeds, but haven't found the problem yet. Is it harmful to over fill the t-case?? It was like this when I bought it. (maybe someone over filled it to hide the slight whine??)Thanks,

Garry

 

[TCluff]

i would start with checking the electrical connections and clean them really good, add some light electrical contact grease and retry if it still does it, i would check my schematic and connector to see if you have power somewhere your not supposed to, if that is not the case i would go after the shift motor, one thing might be worth trying, if you unplug the plug on the motor section, and leave it unplugged, the transfer case should stay in 2wd but you will have a service 4x4 light on, then drive it and see if it still goes into 4x4 and then you would know if its electrical or mechanical... sorry if i confused you...

 

[Garry Verheyden]

Thanks, I'll try cleaning the connectors off. The underside of the truck could use a pressurewashing anyways. I did see the service 4x4 light come on for a few seconds too. Hopefully it was electrical related.

 

[sag2]

I have seen several doing the same thing. It has been the A/C pressure transducer taking out the 5v reference. When the voltage gets to the right point it thinks you selected 4x4. The 4wd switch is a mux circuit that operates on different voltages through resistors. You can unplug the connector so it will not try and make the shift, but it is an electrical problem only. The shifter motor can not make the shift on it's own. And you do not have to worry about a shift to 4lo, as long as the control head sees wheel speed it inhibits the shift. Now if your stopped it can make the shift but you will know it immediately. A shift to 4hi will also be noticed when you make the first turn.

Now to diagnose, tap your DVOM into the 5v wire on the A/C transducer and see if it stays at 5v (actually 4. 9-5. 1). It should stay there all the time the key is on. If it does not, unplug the transducer and watch the voltage. If it stays at 5v then you found the problem.

And don't overlook the rest of the 5v reference or any of the sensors on a 5v supply like MAP, TPS, coolant, cam or crank etc.

 

[Garry Verheyden]

Thanks Sag!! I hope your right. A dumb question to you, where is the transducer located? Close to the A/C compressor?? Are they cheap to replace? One more thing, I pressure washed under the truck today after degreasing. The connections on the t-case were oily and very dirty. Could this have affected the voltage as you said? Thanks again,

Garry

 

[betterthanstock]

The most likely culprit is the switch and the wiring to the electronic controller, or the controller itself. Unplug the switch and see if it stops (it will set a code). If it stops, buy a new switch. If it still does it, it may be the controller.



But if it only started after you pressure wahed, then look at those parts first.

 

[Garry Verheyden]

Do you mean unplug the switch on the dash? Thanks,

Garry