Ok all here goes, if I can't find the answer to this question here, I Don't know where else to go. I have three selections in my Expy for 4WD,they are AWD,4hi, and 4 low. This is the first AWD vehicle that I ever owned, so I don't know how it's supposed to act! 4HI works great, and 4 Low works great also, But in AWD the indicator light on the dash flashes on and off. I also got stuck in a rutted construction site last week. I put it in AWD, hoping to pull out, but no chance! Had to lock into 4HI and right out. Is AWD supposed to pull all wheel at the same time? That would be my guess. But I could be wrong. I also heard that AWD has a coupling in the driveline that senses which wheels are slipping and transfers power to the others. If this is true, the back wheels were burried in mud,and spinning like crazy! It should have put power to the front, correct? If anyone else has any input into this it would greatly be appreciated!

 

Well, judging by the hoards of replies to this problem,I guess that noone else has had it either. I guess I'll be calling the shop tomorrow to see if they have any ideas!:-(

 

[updated:LAST EDITED ON 27-Sep-02 AT 10:35 AM (EST)]AWD works essentially like this: While driving on a grippy surface, the vast majority, if not all of the power is fed to the rear wheels. Upon encountering a slippery surface, the system monitors the rotational speed of the front wheels and compares this speed to that of the rear wheels (I believe the ABS wheel speed sensors play a role in this). If the rotational speed of the rear wheels is dramatically higher than the front, the system assumes that the rear wheels have lost traction and begins to divert power to the front wheels until the rotational speeds of all wheels is roughly equal. The system then assumes you have regained traction and after a very brief interval cuts off power to the front tires. I have been in situations where the system has cycled off and on very rapidly, almost in a machine gun-like cadence. In those situations, I switch to 4HI until I am out of the problem area. This system does not directly activate any locking or limited-slip feature of the differentials. The rear limited-slip, if you have one, is purely mechanical and works as most limited-slip differentials work in any rwd or 4wd vehicle.

To me the AWD feature is a waste of equipment, meant to mollify soccer moms and the mechanically dimwitted who refuse to remember to manually turn 4HI on and off.

 

Thanks for the reply, that is what I thought it would do also, still don't understand why the A4WD light is flashing and 4HI and 4LOW light solid. It just seems like if the other lights come on solid, that the A4WD light should come on solid too, Don't you agree?

 

I thought perhaps the AWD in the original post was inaccurate. The '97s have A4WD which is much different than AWD. From about 2000 and up the truck comes standard with AWD as the default power application allowing the driver to select 4H or 4L. AWD performs as stated in that the touque of the wheels is sensed by the transmission and power is applied to the wheel in need (without limited slip only one wheel at a time will have drive power). A4WD is a user mode to enable to driver to put the truck in mode where some power is always applied to the front wheels through the transfer case. Until a torque mismatch occurs it will be about 90% rear drive and 10% front drive. This is more costly in fuel efficiency on a surface with resonable grip but will help the driver out in a patchy slick condition like icy spots (I've only heard about them down here in FL).

When selecting the drive train sub-mode the indicator light should be out for a couple of seconds and then come on steady. This indicates that the commanded mode has been accepted by the transmission computer and it acknowledges that it is available. The lights for 4H and 4L seem to be responding correctly and indeed you did get the appropriate response from the truck. If the A4WD light is flashing at you, there is a fault in the system. The codes for the power train can be read using an OBD-II reader. That should give you an idea as to the fault. Some auto parts stores will read the codes for free. The dealer will want a services fee (usually about $75) for the same service. One can buy a code reader for about the cost of 2 visits to the dealer. When you find out what the codes are write back. But for now 2 wheel drive will work a lot better than A4WD on your truck.

 

 

>I thought perhaps the AWD in the original post was
>inaccurate. The '97s have A4WD which is much different than
>AWD. From about 2000 and up the truck comes standard with
>AWD as the default power application allowing the driver to
>select 4H or 4L.

Didn't they revert back to the 2HI-A4WD-4HI-4LO switch in 2003? That's just what I heard, haven't verified.

Chris