Symptoms
Lever or button in 4WD but only the rear wheels drive, and the 4WD light stays off. On a part-time truck, a slow tight turn on pavement should make 4WD bind within about thirty feet. No bind means no front drive (Toyota-4Runner.org).
The fix, step by step
- On 1996–2000 trucks the front axle is engaged by vacuum.
- With the engine running and 4WD off, check for vacuum at the twin VSVs on the driver's-side fender wall.
- No vacuum: check the check valve to the intake manifold, the hoses and the reservoir.
- If one hose has vacuum, engage 4WD and see whether it moves to the other.
- If it moves but the axle doesn't engage, suspect the diff actuator or its line.
- If it doesn't move, mark and swap the two hoses: if the truck now goes into 4WD the diff is fine, and a test light shows whether the transfer-case switch signal changes sides.
- Signal but no change in vacuum means a bad VSV.
- Check the fuse and the ADD relay too; one 1998 SR5 owner found it behind the passenger kick panel. 2001–02 trucks use an electric front actuator, so the vacuum tests don't apply.
- On push-button trucks the transfer-case actuator motor can quit when its magnets come loose.
- One owner rebuilt his (1996 Limited, A340F, actuator 36410-35040) by re-gluing the magnets and fitting a new O-ring.
Tools & part numbers
- Hand vacuum pump with gauge
- test light
- marker
- 12 mm and 10 mm sockets
- dielectric grease
Where to buy the parts
Vacuum hose assortmentAmazon ↗
Hand vacuum pump with gaugeAmazon ↗
VSVs, ADD and 4WD actuators (RockAuto catalogue)RockAuto ↗
Hunting a used or discontinued part? Search eBay Motors for Toyota 4Runner 3rd Gen parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.