1ST time 4wd owner (3 months)... was told 4wd had problem when i got the truck....the only thing I noticed was occasionally at about 65mph it would try to shift into 4wd all by itself..it would start a gear grinding noise..i would hit the brakes and slow down fast ...at about 15-20mph it would shift into 4wd with a clunk..I would then hit the 2wd button and it would go back....I was 45 miles from home last nite and it did it again... only this time it stayed locked in 4wd wont shift back to 2wd no matter what I tried to do ...ie: shift on the fly (at speed or slow).... shift while stopped (in or out of gear or parked)....even tried backing up and doing it all over again... drove 45 miles home parked it....so the question is....(I know long time getting here)......Is there an electrical way (fuse or disconnect) to disconnect the 4wd? (hopefully its an electrical problem)....if not a mechanical way?.........cant get it to a mechanic till after the holidays .... thanx for any help...suggestions...troubleshooting tips....etc... Scott.... .................. .................................................. ................................. ...................... also have a lighting issue...when I start the engine.. headlights and tailights come on and stay on.... I have no control of them... thanx again.

 

Remove the negative battery terminal, that will probably cause the TCCM to reset. I would also make sure all the connections to the Switch and the TCCM are clean and free of corrosion

 

thanx for the reply will try that when i have more time... but back to the question ... can I just pull a fuse or something to kill the 4wd for now?..

 

Oh yea, there is a 4WD fuse

 

well, I found the fuse and pulled it nothing changed...still locked in 4wd... will try pulling battery next....

UPDATE MORE INFO: When truck is turned off, axle going to front end spins freely... as soon as engine is turned on, axle will NOT turn by hand. does this mean 4wd is disengaging when engine is off? If so, does this mean that there is no mechanical problem from the transfer case to the front end, and the problem is in the switch or tccm? can I then disconnect the vacuum line (and then plug it) to the actuator to get it to stay in 2wd? ....if this works at least I can use the vehicle till I can figure out the real fix... thanx for your help people.....................Scott

 

From the sounds of it, vacuum is being applied to the front axle engagement actuator which is in tern engaging the front axle whenever the engine is running. This is not the intended operation.

 

Did you try putting it in neutral then selecting the 2hi button? It works on mine...Not sure what year yours is but on my 2001,there is a button just below your headlight switch. If you push it in and out twice,it should chime,thus turning off your daytime running lights. Hope this helps.

 

thanx for the reply.... tried the neutral thing didn't work..... aslo the button doesn't do anything...lights are on always .... even the tailights... always thought "daytime running lights" meant the headlights only...gonna try getting rid of the sensor with a resistor.

thats what I am thinking...now to find out why!

 

You don't say what year so I'll take a shot in the dark and assume it has a vacumm selenoid switch in the center top of the firewall that will have two air hoses and a small electrical connector on it.


This selenoid kicks when signaled/powered to and then opens an internal valve to the primary vacuum that then allows the vacuum to continue to the front axle actuator through the secondary hose,


located under the battery tray which in turn pulls a cable to the front axle to engage it.
If you disconnect the air line running between this selenoid and the actuator under your battery tray and cap it off that should be the work around until you find the cause. You could also disconnect the electrical plug on the selenoid to see if that is either stuck open -at fault leaving the vacuum always on, or if it is working and responding to a faulty signal to it, which would point you back to the TCCM and connections there or the dash switch.

 

thank you.... this is very helpful....first time I even heard there was a vac. solenoid!...will try that today.

oh... and the truck is a 99

couldn't find a solenoid? wrong year maybe? and i see the edit feature now ...thanx swartlkk............ updateulled fuse again, this time, 4wd disengaged...will leave it out till tomorrow then put it back and try the on off ignition sequence thing to try and reset the encoder...i think that's it......... update...2: put fuse back in and tried the ignition sequence thingy..(cycle ign. on/off 5 times)...went back in 4wd....pulled fuse back out... back to 2wd......picked up tccm from junk yard from a 99 that came in on friday..(truck is hardly touched yet... just dash ripped out)...for 5 dollars ( i think thats a steal!!) and a new horn for 5 more dollars...and a trim moulding for above the bumper (under the grill) for only (you guessed it) 5 dollars..... 15 bucks would have paid that for the moulding!!... gonna try that..... but it think its the encoder motor....