Symptoms
One or all locks refuse to engage or drop out, indicator lights flash or stay off. The fault is usually actuation, not the differential. On a 2005 G 500 an MBWorld owner found the centre lock vacuum-operated and the front and rear locks hydraulic, so check both circuits. Mercedes' 2013 US and 2016 Canadian booklets confirm the G 550's lock mechanism runs on brake fluid from its own reservoir; whether your year's centre lock is vacuum-operated confirm in manual for your year.
The fix, step by step
- Follow the same path MBWorld owners use on earlier W463s: confirm vacuum at the transfer case, then work back through the reservoir, lines and switchover valves with a gauge teed into each segment until you find the split line or connector.
- Exercise the locks regularly once fixed — disuse is their enemy.
Tools & part numbers
- Hand vacuum pump with gauge
- vacuum tees and line
- replacement connectors
Where to buy the parts
Hunting a used or discontinued part? Search eBay Motors for Mercedes-Benz G 550 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.