PilotAlan

So, the last few weeks my brand new GLLK has been having intermittent speedometer errors. Let me explain.

I'll have the cruise set at, say, 50. The car is stable at set speed, the digital speedo says 50, the analog says something less, say 40. (the errors have been between 6 and 15 mph, not always the same amount of error)
The error says constant. If it's 10 mph, it will stay at 10 off as I accelerate or decelerate, so at 70mph or at 30mph, it's still 10mph off.

When I decelerate to zero, it will usually reset (like the analog speedo is trying to read negative numbers and it figures out something's wrong). Sometimes it doesn't, and when it doesn't reset the error is not the same as it was before the stop.

An engine stop and start will completely fix the issue for a while.

After the last time, the dealer did diagnostics and got no codes. They tried to replicate it, but you know it is trying to replicate intermittent problems. The lead tech says he's never heard of this, it's not a known issue.
It's going to the dealer next week.

Anyone have any ideas?

PilotAlan

Bump. No one has any ideas?

CharlieX

Every time I have intermittent issues, it seems the dealer can't reproduce.

Don't do this because it's dangerous: have your cell phone ready to snap a quick photo next time it happens. It would also be interesting if you had a GPS app that gave you your speed and see which speedo is correct.

Good luck.

PilotAlan

Thanks Charlie. I took about 6 photos at different times over a few days showing the issue. Send them to my service advisor, he showed them to the shop foreman. It's going in on the 3rd.
As soon as I can get them uploaded off the phone I'll post them here.

The digital speedo seems right (and the cruise is guiding off the digital speedo). The analog is all over the place.

Gravey

Hi
I am having the same problem with my 62 mercedes bought in september C Class sport plus.
To start with it just happened about once a month the digital speedo seemed correct but the analogue speedo . The 1st time it was out by approx 10 mph on the motorway Digital 70 mph/analogue 60 mph. When the car came to a stop it corrected itself and did not happen again for about a month. 2nd time on A road Digital 40mph/analogue 25mph. Again when the car came to a stop it corrected itself. Another month passed then it happened for the 3rd time. Varied between being 10 to 15 mph out then after a stop it improved and was only about 6mph out then after a longer stop corrected itself. A month later again and the problem has happened again, only this time it seems to be happening each day I drive it. Now it seems to fluctuate between being right, a little bit out, and a lot out. The analogue needle now seems to stick sometimes at about 43mph even if I am doing 60, but sometimes it does not. Dealer has had it in once and couldnt find a fault, recalibrated it, but the next day it was doing it again. They are taking it in on Monday to have another look. Did you manage to get yours sorted out?

PilotAlan

Yes. Some supplemental info. Mine seemed to be temperature dependent.


We had a vicious cold snap here, and when the car was cold, the analog speedo would swing to 42-43 mph then stop dead. I could accelerate to 100, and it would stay at 42.
Then when I slowed from peak speed, the speedo would swing down (so decelerating from 100 to 80 on the digital, the analog would slow from 42 to 22).


Once the car starting warming up inside, the speedo would 'drag' accelerating through 42-43mph, and would be a few mph off.
Once the car was completely warm (like a warm day), the speedo acted normally.


No codes, the dealer replaced the instrument cluster. They also said they have seen similar behavior on a coupe of the loaners in C and GLK class.


I suspect a manufacturing defect in the mechanicals of the cluster, and when cold, something is mechanically impinging on the analog mechanism.

Gravey

Thank you for the information, it seems to be very similar problem. We are having a cold spell at the moment and did about a month ago, but not really in October when it 1st happened. I will pass this infomation on to our merc dealer when we take the car in and cross fingers it can be sorted out, although I dont really want the car taking apart and a new speedo putting in. I will let you know how we get on.