I had someone install a separate switch so I could use 2WD Low range. The way he said it to leave it was in the on position. I am not sure how the 4wd system works in our trucks but I can no longer use the 4wd switch to engage my front tires. I have to get out and manually lock the hubs. Can someone clue me into how our 4wd system works and if I have screwed something up by leaving that switch in the on position all the time?


Thanks

 

I would assume the switch that was installed opens the circuit to the Pulse Vacuum Module thereby preventing the engagement of the front Hubs via the ESOF. Have you attempted to engage the 4x4 with the switch in the opposite position?

 

Yes I have tried with the 2wd low switch in the "on" and "off" position. The switch was left in the "on" position so I wonder if it burned up the pulse vacuum module (if that makes any sense).

 

Not likely as the PVM would need to be disabled to prevent engagement. You can check for 12VDC at the connection located on the passengers fender above the Vacuum Pump when 4x4 is engaged. But only for 15 seconds. You'll need a helper or long leads.

 

So if it is not the Vacuum pump then do you think my hubs are not working correctly? They work if I manually switch them.

 

The ESOF hubs are vacuum operated, so if the vac pump is dead or if there is a big vacuum leak they will not work. Usually the pump is ok and the hoses from the frame rail to the hubs rot away. Then you get a vacuum leak and your HVAC vents go to defrost position and stay there. Feel the hoses for damage, and let us know if you hear the pump kick on for a while when starting. And if your vents work properly.

If you can switch the hubs manually that is a good sign.

Let us know how the PVM checks out as Tom suggested.

 

I have no way of knowing how your friend altered the wiring. We can advise on what we know, but mysteries will skew the accuracy of our input. To address as much as I can: