Hi, we've just had 2 feet of snow here in northern england and the 4wd has stopped engaging.

When I push the button for either 4hi, 4 lo or auto it flashes, the thing in front of the passenger seat clicks and something is heard underneath trying to engage but the lights on the swithes do not become solid and the front wheels are ever engaged.

both the 4 hi and 4lo both recently worked, though the auto has never worked.

(it is a 2000 LT with 45k on the clock)

any ideas? I have tried disconnecting the battery for 30 min but it has not worked.

 

First, pull the connections at the switch (dash), TCCM (behind the passenger side kick panel just ahead of the door), and encoder motor (on the side of the transfer case) and make sure that all of the terminals are clean and corrosion free.

While the switch is out, test the resistance for each button push. The link below details the wiring and resistance values for the NV236 transfer case controls:
NV236 Wiring Information

Put it all back together and check the operation of the 4wd system.

If it still doesn't work, check for proper signal to the vacuum solenoid located near the center of the firewall above the distributor. The solenoid should have power on pin A (brown) whenever the key is in the 'RUN' position. When you select Auto4wd, 4LO, or 4HI, pin B (gray w/ black stripe) should go to ground. When in 2HI, pin B should read open to ground.

Beyond that, a scantool may be required to access the TCCM and do further diagnosis.