A couple of months ago, the front passenger seat in our GL starting feeling "loose." That progressed to the seat rocking backward and forward to annoying degree as you accelerated/deaccelerated. After taking a look at the underside of the seat, I could see where the slop was coming from, but wasn't sure of the cause. There is a junction of parts at all four corners of the seat frame held together by pins that are threaded on the inboard side. The junctions at the front of the seat were the cause of the issue.


Junction held together with a pin that is the source of the rocking (both sides on my GL). The nut threads onto the pin after passing through the seat frame and WSS.


The pin looks like it isn't fully seated on the outboard side so I assumed that tightening it via the nut would fix the problem. Additional torque on the nut resulted in a pin that broke near the end in the thinner threaded section. I couldn't find any posts in the X164 section on the problem, but did find a post in an E Class section from someone who had the same issue. There is a bushing that isn't visible before disassembly that falls apart, leading to slop between the pin and the holes is passes through.


The junction with the pin and WSS removed. The failed bushing is circled.

In order to get new bushings from MB, you have to buy a repair kit that includes new pins, bushings, nuts, snap rings (that hold the bushing in place) and grease for the low, low price of $280 at my local dealer. I decided that was a little much for the product being offered, and discovered that if I wedged small pieces of wood in the junction, the seat no longer moved. That was a great solution for about 3 days until the SRS warning light came on. More research led to the discovery that the little box on the inboard side the pin passes through is a weight sensor (the WSS) for the airbag, and my fix was causing them to not function correctly triggering the SRS warnings. I found a vendor online (mbpartscenter.com) that sells the kit for $176, which is still ridiculous, but a little less painful at least. Directions with the torque specs are attached (5 nm on the easily broken pin). It is pretty simple repair. A tray below the seat with electronics has to be loosened and moved to get at the bottom bolts on the WSS, and you'll need a snap ring tool get the the remnants of the old bushing out/install the new bushing. There isn't much clearance on the inboard side of the seat, but you can get the pin in/out without dismounting the seat from the vehicle. If I hadn't broken the pin, I would have just tried to find a source for a bushing of the correct i.d./o.d. to add to the old bushing to replace the section that disintegrated or use something to build up the diameter of the pin rather than buy the kit.


The repair kit, with the old bushings next to the new ones for comparison. The pin with the junk on it is one of the old ones with grease/bushing bits.

Unfortunately, the SRS warning light and error message still appear even after reconnecting the battery and driving around with a passenger in the seat. Despite having an option to turn off the error code, my icarsoft doesn't clear the error message or warning light, so a trip to the dealer is probably required to clear it once it is set.

 

Great writeup. Thanks.

So the bushing acts as a spring for the scale (WSS)? Ugh, that's terrible.

 

Happy to do so. I've saved a bunch time and frustration fixing things using guides others have put together.

I didn't give them a squeeze test, but the center part of the bushing looks like a reasonably hard plastic so there probably isn't much springiness in the bushing. Apparently when WSS sensors are replaced, dealers have a device they put on the seat that replicates a person and weights are added and the system is calibrated. If the dealer wants to go through that procedure with mine before resetting the light, I'll be living with a SRS light. I wonder if a STAR clone can shut it off?