One Blocked Line Was the Real Cause of This Mercedes Soft Top Failure

When Alain’s 2003 CLK 500 convertible started refusing to open its soft top, the usual forum advice didn’t help. The roof would lift about a foot off the windshield and then just stop, even though the pump kept running. Cycling the switch sometimes got it going again, but the failure was random and frustrating.

Closing the top worked perfectly every time, and the car’s diagnostic system showed no error codes. All switches checked out fine, and there were no hydraulic leaks.

Alain went through a long and expensive troubleshooting process. He had both main lift cylinders and the rear window cylinders overhauled, and he replaced the entire pump assembly. Still, the soft top kept failing. That’s when he switched to a mechanical approach. He found that even manual opening was impossible on some attempts, so he began disconnecting cylinders one at a time.

When he disconnected the left main lift cylinder from the frame, the roof opened manually without any trouble.

That led him to bench-test the cylinder itself, which moved freely. So he turned to the hydraulic lines connecting that cylinder to the pump. The left main lift cylinder is unique in the system, it has three lines. By raising all three and testing flow, Alain discovered that line 12 was completely blocked.

After blowing compressed air through it for a while, the line cleared. He reassembled everything, and the soft top worked perfectly. His advice to other CLK owners: before replacing expensive parts, try checking for a blocked hydraulic line. A simple blast of compressed air might be all you need.