Occasional no start/slow start - S65
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Joined: Feb 2026
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Occasional no start/slow start - S65
2016 S65 28K miles
Approximately 10% of the time on cold starts, my car fails to start (no crank) once or twice and then starts with a slow, long crank on the second or third try. This has been going on since I bought the car 9 months and about 7K miles ago.
Warm starts are always flawless.
It has never totally failed to start. Three tries was the worst and that has happened only 3-4 times.
I replaced the battery with no impact.
The MB shop I use and believe to be very good cannot find anything amiss. There are no warning lights or codes.
It does not get worse if the car has been sitting longer. It can start right up after sitting for ten days and it can fail to start after sitting one day.
Possibly related: one time recently after starting just fine cold and then driving 75 miles flawlessly, I got off the freeway and into surface street traffic. At about the third red light I hit, while sitting still the RPMs dropped severely and the engine felt like it was about to stall. It corrected itself immediately and worked flawlessly the rest of the day.
Possibly related: occasionally at idle the engine feels slightly rough. Not truly rough, but not that dead smooth V12 feeling.
I do not have service records, but I do have the VMI from when I bought it. It does not show that any of the components involved in fuel or spark have been replaced.
Any thoughts, suggestions, similar experiences, or advice would be appreciated.
Approximately 10% of the time on cold starts, my car fails to start (no crank) once or twice and then starts with a slow, long crank on the second or third try. This has been going on since I bought the car 9 months and about 7K miles ago.
Warm starts are always flawless.
It has never totally failed to start. Three tries was the worst and that has happened only 3-4 times.
I replaced the battery with no impact.
The MB shop I use and believe to be very good cannot find anything amiss. There are no warning lights or codes.
It does not get worse if the car has been sitting longer. It can start right up after sitting for ten days and it can fail to start after sitting one day.
Possibly related: one time recently after starting just fine cold and then driving 75 miles flawlessly, I got off the freeway and into surface street traffic. At about the third red light I hit, while sitting still the RPMs dropped severely and the engine felt like it was about to stall. It corrected itself immediately and worked flawlessly the rest of the day.
Possibly related: occasionally at idle the engine feels slightly rough. Not truly rough, but not that dead smooth V12 feeling.
I do not have service records, but I do have the VMI from when I bought it. It does not show that any of the components involved in fuel or spark have been replaced.
Any thoughts, suggestions, similar experiences, or advice would be appreciated.
Junior Member
Joined: Aug 2022
Posts: 21
Likes: 6
2004 SL55
Intermittent….This sounds tough. There are two batteries in the car. Might the other need to be checked?
You might go crazy trying to get this to duplicate while at the dealer. I doubt anyone can help if they can’t duplicate the issue.
If it were me, I’d check the other battery and if not it just wait until it gets worse (if it even does) and can be duplicated while at dealer.
You might go crazy trying to get this to duplicate while at the dealer. I doubt anyone can help if they can’t duplicate the issue.
If it were me, I’d check the other battery and if not it just wait until it gets worse (if it even does) and can be duplicated while at dealer.
Member
Joined: May 2020
Posts: 247
Likes: 57
From: Fort Worth
2005 CL55 AMG || 2005 CL65 AMG || 1989 560SEC
check voltage on the unreplaced battery. Fine if warm? other than battery, I'd guess maybe there's a component in proximity to the engine bay that likes the heat. Starter relay or solenoid? Maybe a corroded fuse? Bad engine ground?
Super Member
Joined: Sep 2021
Posts: 537
Likes: 116
From: Ann Arbor, MI
2004 SL600
While the 2016 model is a bit different from my 2006 engine, this sounds like a fuel problem to me.
I would first test the fuel pressure while running, check how quickly fuel pressure builds when starting and check how quickly it drops after shutting down the engine.
My guess (guess!!) is that the fuel system bleeds out when the engine is off and it takes some time to build back up again.
Your symptoms exactly match a typical engine's behavior after the the fuel rail has been removed for maintenance.
We want to be sure that an injector is not leaking as a badly leaking injector could hydro lock the engine and seriously damage it.
I would first test the fuel pressure while running, check how quickly fuel pressure builds when starting and check how quickly it drops after shutting down the engine.
My guess (guess!!) is that the fuel system bleeds out when the engine is off and it takes some time to build back up again.
Your symptoms exactly match a typical engine's behavior after the the fuel rail has been removed for maintenance.
We want to be sure that an injector is not leaking as a badly leaking injector could hydro lock the engine and seriously damage it.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,621
Likes: 1,216
From: Phoenix
222 S-65
OP to be clear you press the start button and it does not crank.... You then hear it crank the engine slowly and it will start?
Check voltage at the starter (large lead from battery) when asking it to crank. Compare that with voltage at the battery when asking it to crank. Voltage figures must be the same at the starter and battery. Voltage drop under 11 volts? Battery isn't up for it or the starter is drawing wayyy too many amps. Verify that ground leads have good connections. Engine to chassis and battery to chassis.
Check voltage at the starter (large lead from battery) when asking it to crank. Compare that with voltage at the battery when asking it to crank. Voltage figures must be the same at the starter and battery. Voltage drop under 11 volts? Battery isn't up for it or the starter is drawing wayyy too many amps. Verify that ground leads have good connections. Engine to chassis and battery to chassis.
Last edited by JohnLane; Feb 4, 2026 at 04:13 PM.
Super Member
Joined: Sep 2021
Posts: 537
Likes: 116
From: Ann Arbor, MI
2004 SL600
Oops, yes, you were clear about the no/slow crank.
As others said, that is a battery problem. What is your front battery voltage? Have you put a battery tester on it? Or, have someone read the voltage as you crank the engine.
As others said, that is a battery problem. What is your front battery voltage? Have you put a battery tester on it? Or, have someone read the voltage as you crank the engine.
