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.