Borderline

There are many threads about turning off the seat belt chime alarm, or an oversensitive alarm going off when nobody is in the passenger seat.

My problem (2008 E350) is that the seat belt chime stays on even while the seat belt in the drivers seat is buckled. It is intermittent: a problem for several days, then goes away for a few days, now it is back. It's been happening for over a month.

I have sprayed compressed air into the slot to see if it was a problem with dirt. That had no effect.

My current hypothesis is that a wire in the seat belt latch (the one attached to the seat, next to the center console) may have been damaged. There may have been a two year old involved who could have stepped on it, maybe causing a wire to come loose.

IF that is the case, I would assume that I need to take apart that piece (it is inside the plastic sheathing I guess?) to reattach or more firmly attach the wire.

Do I need to remove the driver's seat in order to reach this? Or can it be accessed without this step? And if so, is seat removal particularly difficult?

Is it correct to assume that, out of warranty, there's not a way to get a dealer to fix this for free?

THANKS.

Plutoe

If you have confirmed that it is a frayed wire, that is one case.(No seat out)

However most of the times it is the respective buckle switch that goes bad---if that is the case the seat has to come out. The other bad news is that the MB buckle switches are only sold in pairs.

PS: Seat removal----be patient

Borderline

Well, I have not confirmed it is a frayed wire. Any idea how to diagnose which one is the problem? I didn't know that there was a buckle switch. Were is the switch located? It is easy to replace? Online source? Sorry for these basic questions.

Plutoe

Disconnect the connector grab a multi meter and do a continuity test.

The buckle switch location-----you already found that---"My current hypothesis is that a wire in the seat belt latch (the one attached to the seat, next to the center console) may have been damaged"

It is easy to replace-------NO

Online source?--------NONE a dealer item

Read your owners manual-------Sorry for these basic questions.

Borderline

Well, I got the seat unbolted and I was able to twist it towards the driver's side, so I didn't need to unplug anything under the seat. But I could not figure out how to get into the seat belt latch to check on the wire connections. I unbolted the assembly from the seat, but still couldn't get into the plastic sheath or the buckle latch itself. Alas. I would guess that a dealer would just replace the whole thing. That might be my next option unless anyone has a better idea.

Plutoe

You are absolutely correct. The seat belt latch switch(female) is replaced if the latch switch is faulty-----however we suggested that you disconnect the latch switch from under the seat and test with a multi meter(before removing the seat)----you chose not to do that-----now what is your issue!!

Borderline

I appreciate your comments. Sorry, this is going to be long.

Perhaps I misunderstood you originally. When you say "Latch switch" you are talking about a switch that is inside the seatbelt latch that, when the seatbelt is buckled, closes a circuit that tells the instrument cluster not to sound a chime when there is a person in the seat who is unbuckled. So there is a combination of seat sensor (weight of person) and buckle sensor.

The two hypotheses for the problem were (1) bad latch switch or (2) frayed/partially disconnected wire running from or into the buckle switch.

I preferred the second hypothesis because I had evidence that my son was stepping on the latch assembly, and if it were bent it could have possibly damaged the wire. Also, the chime was intermittent, and if I bent the latch assembly one way or another, I could make the chime stop. I could imagine that a bad switch could possibly yield intermittent chiming, but it would be more likely that a failed switch would cause the chime to be constant, regardless of the angle of the latch assembly.

Given this information, I'm not sure what the multi-meter test would accomplish. I can't imagine a third possibility, and I don't think checking continuity would distinguish between these options, because both would yield the same symptom of "partial" discontinuity.

Opening the seat belt latch assembly would show either: (1) a bad wire connection or (2) no evidence of wire problems. If #1, then I could reconnect the wire (or replace a frayed section, etc.). If #2, then it would be the switch.

Thus, my attempt to gain access to the latch assembly was the direct test. However, I was unable to remove the plastic sheath that is hiding the wires, and I was unable to open the seat belt latch assembly itself, where the wires are attached to the latch switch.

A dealer is not going to open the latch assembly to do any electrical work, they will replace the whole latch assembly. My attempt to determine the status of the wiring inside the latch was in my opinion the only way to determine the cause of the problem.

Now, in your last post you said:
"we suggested that you disconnect the latch switch from under the seat and test with a multi meter". I still don't understand. I'm not great with electronics, but would this test the wiring and not the switch? Am I testing continuity? If it IS the wiring and not the switch, I still need to access the latch assembly to fix the problem. Two black wires are running from the latch assembly to a plug under the seat. If I unplug this from under the seat, and I'm testing continuity between these wires, how would this distinguish between the two options, and how would the repair be different?

So, given this info, let me know if you have any further advice as to how to proceed. Many thanks!

Plutoe

Once again you have confused your self and others------you are now talking about two independent systems---system one--the seat belt; system two seat occupied system.

My opus was about system one, repeat system one the seat belt---that you said could possibly be frayed---that is why I said use a multimeter to check the circuit continuity before removing the seat.Continuity will also indicate if seat belt female end switch was faulty------thats all I indicated.

The seat occupied sensor is very different, however don't you think that a contintuity check on that circuit would be helpfull in determing a so called frayed wire????

Plutoe

You just have to do what you have to do--------all I know is that the female seat belt buckle switch can not be accessed.

If found faulty after testing the circuit with my tool, that part of the seat belt system gets replaced, and when you go to the dealer to try and purchase just one side you will find they will not sell one side. Both sides come in a set and yes as you learned the seats must be removed--Very Good Luck!!

Borderline

I am also talking about the seat belt system. I didn't say that the continuity test wouldn't be helpful to test for a frayed wire. I said that as far as I could tell, it would not discriminate between a bad switch and a frayed wire because the frayed wire is near the switch, inside the buckle latch.

So, if it's impossible to access the seat belt latch to fix either of these problems, which I didn't know until you mentioned it (and couldn't see how to get it open), then it does not matter which one is the problem.

Finally, if a wire is intermittently making the connection, then the continuity test will be ambiguous. The test for "continuity" is that the chime comes on while the seat belt is buckled (in this case it is not making contact) and then if the seat belt latch is moved slightly, the chime goes off (when we have continuity).

Thanks.

W211_2008

Hi all,

I got exactly the same problem with my W211 (E230 - year 2008) starting from last week. Would you advise me what's the resolution finally ? It's really annoying to hear the chime while I am driving alone.

Thanks

fatmanstan

Hi, what's the update on this? I have a 2009 CLS550, and the out of nowhere while 4 passengers were in the vehicle, all buckled in, the seatbelt light came on and the warning chime, and it won't go off. Any ideas?

HD Rider

You can purchase just one latch assembly.
http://www.genuinemercedesparts.com