Symptoms
One or all locks refuse to engage, or engage then drop out; sometimes paired with central-locking oddities. The fault is usually the vacuum system, not the differentials.
The fix, step by step
- Confirm vacuum at the transfer-case hose.
- Then work from the pump and reservoir (front-left wheel well) through the manifold and the switchover valve block on the firewall, teeing in a gauge at each segment.
- One owner’s 2005 G 500 fault was a split plastic connector inside a rubber Y fitting under the brake booster.
- Change transfer-case and diff fluids and bleed the hydraulic locker lines while you’re in there.
Tools & part numbers
- Hand vacuum pump with gauge
- assorted vacuum tees and line
- replacement connectors
- diff and transfer-case fluid
- bleeding kit
Where to buy the parts
Lisle 20300 vacuum gauge / pump testerFCP Euro ↗Amazon ↗
Genuine Mercedes vacuum hose connector 117 078 03 81FCP Euro ↗Amazon ↗
Genuine Mercedes vacuum hose 000 158 14 35FCP Euro ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Mercedes-Benz G 500 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.