Hi all,

My 2017 C43 doesn't always start in the first push of the button. There is a click noise as if the car is about to start, but doesn't. Can sometimes take up to 6 pushes to start - or starts first time no problem. My local specialist said it could be either the starter motor or a voltage dip limiter. The main battery is brand new.

any ideas appreciated
Thanks
Jim

 

How are your VTT? How is the battery?

 

What is VTT?

The main battery is under a month old. It was replaced as a first step to rectifying this issue, but didn't solve it.

 

Don't through anymore parts/labor at this...
Use an MB scanner to run bidirectional tests + read status.

Starters are fairly well built .

Suspect the $2 control relay in the SAM.

 

Variable valve timing.

 

Cali has the advice to take here. I suspect a sensor or relay is failing. Could be Park/Neutral switch or brake switch as well if you dont even get a crank on key press some of the time.

 

My 2017 C43 does the same thing once every month or two. (I should document it for accurate info.) If it starts the second attempt, I blame myself for not holding the button long enough the first time. If it takes more than two attempts, I just pop off the button and put the key fob in the slot and turn.

 

That is very interesting input you confirm:
this is likely a chassis issue rather than OP single car specific.
Once a while your KeylessGo "push button" requires key inserted to start.

Does it "cranks but not start" ?
or just "clicks and no crank" ?

This may just be CAN-B chaos with: KeylessG module + EIS keyslot Switch interacting DoorControl modules.
Beware of sleepless chassis battery drain... CTEK!

We can use a comprehensive scan report to see what's playing out then focus.

 

I was hoping my Merc specialist would have done these kind of tests but who knows... the car is only at 68k miles and i would hope a starter would last longer than that!

 

It clicks, as if its about to start but doesnt make it the whole way. it happens with the button or using the key. But always very intermittent - could not happen for a few days but when it does might start the second time or the 6th push.

How would i deal with either of those you mentioned? sorry not too familiar with the technicals

thanks

 

Without being familiar with the technicals, you have done everything you could. This is a low mileage vehicle with unlikely worned out electricals.

Here is a procedure quick and safe that may help:

1. Turn Ignition ON (all dash lights)
2. WAIT 15SECS. for modules to COM.
3. Then crank it!

Unstable CAN-B Modules need time to network.

I absolutely hate to throw parts blindly at issues without prior testing.

Your car has a dozen good reasons not to start. At least you confirm that KeylessG in slot does not help.

Let us know.

 

Dials sweep, but no noise from starter. It's like the brake is not applied so it's just turning the ignition on. If it does that 2x in a row, then I pop off the button and use the key with 100% success.

 

Great: you have this pretty well defined!

This reads like the drive authorization fails
It is beyond "No crank"...

Nothing to do with SAM, relays or starter.

This may involve EIS + Keyless over CAN-B made unstable by Door modules.

Use an OBD tool to confirm status. We'll try to customize a repair suggestion.

 

Funny - came on here tonight to post about this issue with my 2020 C43 with 81K km (51K miles).

Bought the car in January 2024 and warranty expired October 2024 and I noticed the issue in December 2024. It may have happened a couple times around when the warranty was expiring but I thought maybe I didn't press the brake pedal firmly enough - it would start on the second attempt and was an intermittent issue. Got progressively worse so took it to my local Mercedes dealership (local Mercedes-AMG dealership) where I had previously purchased the extended warranty. It could take 2-5 attempts to start but only intermittently and they replaced the battery on my dime (they couldn't replicate the issue). Over the next couple winter months it happened again so they replaced the the starter (and starter solenoid?). This was all early 2025.

We get to December 2025 and the issue comes back with one re-start attempt required (notified dealer by text) but it got worse over the next couple months by end of January 2026. They took the car back and rn diagnostics and I think replicated the issue once (plus I gave them a video of the issue). They replaced the battery, starter, and solenoid again under the extended warranty this time. Now we're into March a few weeks later and the issue occurs again - mainly when it's cold and the car has been sitting outside overnight or all day.

Took it back in and they found some corrosion on electrical connectors near the firewall that has too much resistance so they replaced those. Called me to pick it up but when I got there it wouldn't start for them so they kept it - that was over a week ago.

Was going to ask if anyone else experienced this issue because the dealership has not seen this before (I think they opened a technical ticket with MB after the last repair didn't work).

Hoping I hear from them on Saturday because the CLA sedan they gave me for the past 3 weeks doesn't measure up to the C43.

OP, is this the same no-start issue you are experiencing?

https://youtube.com/shorts/yolEqC4Wkgc?si=kI5Mr0O5gXQAXcHX

 

This is not "no Start"... this is "NO CRANK".
The dealer technician will have this sorted out in no time with the factory guidance using Xentry shop tool.
It's a shortlist once tech gets to work on this.

 

I was hoping for that but it's the fourth time in the shop and this last time they've had it for almost 3 weeks.

 

Fourth time unsuccessful failed repair...
that's when you can decide on a different course.

Are you familiar with your State "lemon laws" ?
Bad cars can be returned or exchanged.

 

I purchased the car used elsewhere in January 2024 and it worked fine for almost one year before I took it to this MB dealership (opened about 5 years ago) closer to my home for this issue. I didn't argue with the bad battery diagnosis and the issue appeared to be resolved for almost another year before the issue started again. It appears it either takes that time for the issue to develop/affect the battery/starter and/or related to the cold as it never occurred during spring/summer/fall, only winter.

I don't think lemon laws apply at this point. I'll play it out as long as they are trying to resolve under warranty - if I go elsewhere now it may re-start the clock and some electrical issues are not covered under the last year of the MB ELW.

 

This being repaired under warranty the dealer has to obey the factory guidance to get payed until coverage expires. At that point fixed or not, everything will be yours to repair.

The one thing you want to do is nothing the dealer can blame you for causing this.

Beware they can even tell when the hood is open and how long. I would not even float charge the battery if that helps MB keep your car on the road.

 

Car is stock and staying that way until further notice. The dealer knows they've misdiagnosed and repaired the symptom (plus I paid $1K out of pocket to replace the first bad battery which was one of the symptoms), not the cause so it's on them to resolve in my opinion. I have respectful text communication with the SA as a record so hoping that keeps them honest.

 

After 4 failed attempts, it's not unreasonable to be more proactive :
Contact service manager at dealership
Contact customer relations at MBUSA

Express interest in getting your Mercedes back on the road and at the same time preserve interest in your warranty coverage.

Hopefully it will all workout in the end.

 

Fingers crossed - will let them complete this 4th work order which is still open. Dealer service manager is aware and I'm using one of their 2026 courtesy cars so that asset is tied up.

I am curious to know if the OP's issue is the same because this dealership says they have not seen this issue (but it's a fairly new dealer/facility).

 

Did anyone ever resolve this problem? The no-start always occurs for me when the car has been sitting in my garage for 2 or more days. Press the start button. The car will start MOST of the time. If it does not start, press it again (sometimes it starts, sometimes it does not). Press a third time; it almost always starts by now. Once I start the car, the start button works every time for the rest of the day. Day 2: The car currently starts properly 70% of the time, but not always. The dealer's temporary solution is to remove the start button and insert the key into the slot. This has been working OK for now, but I would obviously prefer to work correctly. I will be taking the car to the MB sealer this week for troubleshooting. Thanks to all of you who have posted identical problems in the MBWorld.org forums.

I doubt this problem is related to the key FOB, as I have both original key FOBS, and the identical problem occurs when EITHER key FOB is used to start the car. Has anyone tried replacing the female receptacle where the key FOB is inserted????

This is a 2017 SL550 with 22,000 miles. I am the second owner. Purchased it CPO with 2,800 miles on the clock in November 2017. This current start problem first began in February 2026.

 

I hope to have an update by end of this week. In February the dealer found some corrosion on the (bus?) connection block on the firewall (see photo) that was affecting resistance levels and replaced it but the issue occurred again so they went back to head office/tech and the recommendation was to replace an electrical band/strap/harness that may have experienced some moisture related issues. Don't have all the details but as of Friday afternoon, the part is expected to arrive around Wednesday April 15 (not sure if it's coming from Germany?) then installed. Should have more info about what they specifically replaced by end of week.

 

All the best.