When I hit the 4HI button (4 button) the lights flash but always go back to 2Hi unless I hit 4LO then it flashes and I get a service 4wd light. 4wd auto flashes then steady but 4wd does not engage in that mode. I can hear what sound like relays clicking in the kick panel when I hit either 4hi or 4lo.

I have checked to see that the vacuum actuator is operating properly and it is. My next step is how to determine if the cable is not broken I guess.

If I find that the cable is okay, where should I look next? What sensors are the TCCM looking at to determine if the system is operating properly before it defaults back to 2wd?

Any wisdom appreciated.

 

Dude, check out my recent post. It's called 4WD battle or something like that, I cant even remember. But it sounds like we are having similar issues.

??

Good Luck

 

As for sensors there's two. On the drive axle a switch, is it engaged or disengaged? On (or in that is) the transfer case motor is the encoder which tells the TCCM what range the transfer case is in. When you change ranges if the TCCM doesn't see it complete successfully it defaults back to where you were.

 

if your front diff doesnt fully lock, the light will blink. i put a pull cable to engage my front diff., and i gotta make sure to pull it far enough so the light stops blinking then lock the cable. thats how i know mine is engaged, and once you lock the cable u know it wont go back into 2wd.

 

Thanks for the responses.

hpb182 What I am describing is NOT the same as your situation. My front axle wont engage at all.

redblzr4x4 are you saying you pulled the cable from the vacuum actuator to engage the front axle? Or did you rig a cable to inside the car?

RonJon Thanks for the sensor location and purpose. Since there are no codes to read when the Service 4wd light comes on, this is a crap shoot at best.

I think I will try to pull the cable at the vacuum actuator and see if at least it engages the front. If it pulls all the way out, time to get a new cable As for the range selection, I guess that may have to wait for another day.

I will let you know what I find.

 

while the light is blinking try reving the motor a little. My wifes 99 does the same thing. For the longest time we could'nt get it to engage, then I found that the hose was disconnected from the firewall plugged it in to an empty port, now she revs it a little and wallah she has 4wd. The hill we live on here in wisconsin she needs it or I hear about it.