Join Date: Jun 2006
Location: Eastern ON Canada
Car: 07 OBW 2.5i D-4AT
Feedback Score: 5 reviews
When the fuse is installed, the AWD transfer clutch should remain disengaged, with no effective connection between the transmission output and the rear drive train.
If there were a short, or open, circuit between the transmission control module and the AWD solenoid (duty C), the on-board diagnostics should pick this up, and cause the AT Oil Temp light to flash. So: With the key at ON but the engine not started, does the AT Oil Temp light come on and go out when the engine is started and does it flash at any time, or stay on after the engine starts?
If the rear wheel skips when turning on loose surfaces with the FWD light showing, it could be that power is still being transferred to the rear drive, or it could be a binding rear differential. The first can be better detected if the car is on a slippery surface, where the front wheels can be made to slip when going straight (e.g. slippery upward slope). If the AWD is disabled, the rear wheels shouldn't spin (whereas when the AWD is working, if one or both front wheel spins at least one rear wheel should spin as well). If the AWD clutch is still (incorrectly) engaged, the rear wheels (also on the slippery surface) will tend to spin as well. (You will need one or more extra people to watch the front and rear wheels to be sure of what is actually happening -- don't depend on sensing this from the driver's seat.)
If the rear wheels spin even with the FWD indicator, then the AWD clutch is not disengaging. This could be caused by a malfunctioning solenoid or transfer valve (they work together) or mechanically binding transfer clutch plates. The first can be verified by checking the hydraulic pressure being sent to the clutch. There should be a port on the side of the transmission extension case for this, but I don't have details for the 1998 transmission. If the pressure remains high when the fuse is in, then the problem is clearly the solenoid. If the pressure is low, then the problem is probably mechanically binding clutch plates. In any event, it means taking down the extension case and replacing the solenoid and possibly the clutch.
If the rear wheels don't spin with the fuse in when going straight on a slippery surface, yet one rear wheel skips when the car is in a tight turn, the problem could well be in the rear differential.
Have you owned the car from new? If you're not sure if the ATF was changed, then doing multiple changes with some running in between could work (if the problem is related to the fluid or gummy deposits) and would be worth a try.
There is no fixed, preset AWD clutch engagement in manually-selected gears. The rate at which the AWD clutch pressure is increased in response to various parameters such as the throttle position and engine load is more rapid in the lower gears (1 and 2), but there's no gear in which the power to the rear is maximized at all time.
Using second gear when starting off on a slippery surface is often recommended for both MT and AT cars of all makes. The reason is that in second gear, less torque is being applied to the wheels because of lower transmission torque multiplication, and this lessens the tendency for the wheels to break loose and spin.