Actually I know how Control Trac works in theory, but I mean in the real world. For example when going through emissions we put it on the standard, rear wheel only rollers. If I understand it correctly, both driveshafts are always turning and if the system detects the back driveshaft going faster than the front it interprets this is as a loss of traction and can route up to 100%of the power to the front wheels. So how, when it was in auto 4X4 mode, was it able to go on the rear wheel only rollers? I am (assuming) that both driveshafts were turning at the same speed so the system didn't send any power to the front wheels. I know the 4X4 high and low work fine.

 

If your system is working as designed, there should be no way that the test can be performed without all wheels on rollers.

Any differential in rotation between the front and back (hall sensors) would trigger the module to supply 12vdc to the electromagnetic clutch in the T/C. ... Philip

 

I am not the one who actually did the smog test. I just thought he said he put it on the single rollers but I could be mistaken. 4X4 works fine, I tested it.

 

Mine is a '98 with "Automatic" on the dial as the standard setting. Not sure if they called in "Control Trac" in '98 or not, and too lazy to look it up. The system automatically engages the front if the rears slip, just as the prior poster indicated. I've had it engage on wet and icy conditions.

If you put it on single rollers, best clear a path in front of it, as it's going to engage the fronts very quickly.

My smog tests are done off the rollers in Park.

 

Thank you all for the answers. I took my Explorer to my local, trusted shop and asked if I could use one of their lifts to get all four wheels off the ground, so we did that and someone got in the truck and test all three ranges (auto, high, low) and all four wheels were turning in each range. With the auto 4X4 setting I put my hand on the front tire and could not stop it. There is no way that this truck was tested with a single roller. Everything is working as it should and I think I misunderstood what the seller said about the emissions test. Because if those front wheels were on the ground instead of a lift, and with the rears on a roller, the truck would definitely go forward.

I'm still just a little bit confused about the difference between 4X4 auto and 4X4 high. I think that I got now though, but please let me run it by you to see if I do. On 4X4 auto, all wheels turn but the computer tells it which wheels to send the most power to, like if one wheel is slipping it sends more power to other wheels; and I would assume that for normal street driving it sends most of the power to the rears. Just a guess. However in 4X4 high the computer locks them so that the power is sent equally to all wheels. Is that about right? I also have the LS locker rear end if that comes into the equation.

Thank you!