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I have a 2008 s550 with about 132,000 miles on if a couple of days ago I noticed having some sluggish starts but the day it went out complete before I have to call a tow. I was running errands about 3 of them and everytime I start the car the starts got sluggish and sluggish until my last errand went into the store and came out and nothing no crank no nothing… I had my mechanic check voltage on the main fuse box under hood he said it was good 12v than he went onto the battery side and the terminal wiring read about 9volts (he dug the voltage reader past the black. he said something isn’t getting enough power. Just from anyone having experience before I get it towed to the shop what else should I be looking at? Thanks in advance I like to learn also when problem arise this side is having low voltage
Last edited by JaneDoe702; Jul 27, 2025 at 01:45 PM.
I have a 2008 s550 with about 132,000 miles on if a couple of days ago I noticed having some sluggish starts but the day it went out complete before I have to call a tow. I was running errands about 3 of them and everytime I start the car the starts got sluggish and sluggish until my last errand went into the store and came out and nothing no crank no nothing… I had my mechanic check voltage on the main fuse box under hood he said it was good 12v than he went onto the battery side and the terminal wiring read about 9volts (he dug the voltage reader past the black. he said something isn’t getting enough power. Just from anyone having experience before I get it towed to the shop what else should I be looking at? Thanks in advance I like to learn also when problem arise this side is having low voltage
Have battery load-tested in auto parts store like AutoZone. Just measuring voltage does not tell how it is. Do you know how old it is?
Check the battery terminals and cables for corrosion or loose connections clean or tighten them. Also test the battery itself (even if it shows 12V, it may fail under load). If that's good, suspect the starter or ignition switch. A voltage drop test along the starter circuit will help pinpoint the issue. Could also be a bad ground connection. Let us know what you find.
Have battery load-tested in auto parts store like AutoZone. Just measuring voltage does not tell how it is. Do you know how old it is?
If battery ok I would look at the starter.
do i know how old the battery is? if thats your question my mechanic got me 2 batteries one with 860 cca which was way to long to fit than i another “new one which was 550 cca i ended up trading the 550 cca for a guys used 800 cca battery… when i was waiting for a tow i had got a jump and still no crank and when road side assistance came they had a portable battery jump and still no crank. is there any parts of the car I should be looking at to see if there’s any loose wiring? thanks for responding
do i know how old the battery is? if thats your question my mechanic got me 2 batteries one with 860 cca which was way to long to fit than i another “new one which was 550 cca i ended up trading the 550 cca for a guys used 800 cca battery… when i was waiting for a tow i had got a jump and still no crank and when road side assistance came they had a portable battery jump and still no crank. is there any parts of the car I should be looking at to see if there’s any loose wiring? thanks for responding
Test the starter. Go under car and connect thick main starter cable post to the trigger wire post. This should always start the starter motor. If not you have bad starter.
went to make sure my battery was 100% and still nothing
meaning ?
to test a battery you need a load tester good ones cost about $600 few have these at home and not many garages know what they are doing either
arrie's post eluded to issues with starter motors - this is not uncommon on later 221s
Meaning I went to my nearest auto zone for them to charge my battery it was at 69% so let them charge it to 100 brought it back to my car connected terminals and still nothing
cars get pre-fuse boxes with fusible links than can pop if something nasty happened
thanks for reply i can double check… it’s just that before all this happened my car was sluggish upon starting the car but it did turn over until my last errand.. but I will double check
glanced at the first post.... you can't fix A 221 with guess work and hope
needs decent diagnostics and when being silly a lot of skills and experience
that said where he said u have only 9v - this module beside the battery has been known to go strange
If you're not going to get it to a Benz dealer and hooked up to Star, then I would still start with replacing the battery with a new one off the shelf, not a "new/er" on with a history. Brand new, never used. It's always the battery.
If you're not going to get it to a Benz dealer and hooked up to Star, then I would still start with replacing the battery with a new one off the shelf, not a "new/er" on with a history. Brand new, never used. It's always the battery.
thanks for your response do you recommend a battery? I have a brand new battery but it’s way to long to fit in the battery slot and I can’t even test it because my terminals really only fit here’s when I took it to autozone to get the one traded it had 68% but when I picked it up it read 100%
a battery that can actually fit.. terminals are to short
Last edited by JaneDoe702; Jul 31, 2025 at 12:42 PM.
the cars had a cross over from two batteries, to a large battery up front - the twin battery ones have a small in the front - and a very large one hidden at the back of the trunk, accessed ONLY via the trunk after removing the trim - its behind the right rear seat)
the photo you gave in the first post would indicate you have the twin battery set up - and the front battery is a small 350cca one just to crank the engine - in the trunk is a massive one that does all the rest of the cars electrics
the idea is the back can help the front but not the other way around - as no one sees it - the rear one is often in a right mess - not that I believe it should stop the car starting if a good one is in the front - a naff rear battery certainly makes the car have a hissy fit - and as so much of the car relies on healthy volts from the one in the back - and you are getting nowhere - it might be worth fitting one at the back - it should be an AGM battery
it would be sensible to have the front disconnected and do not short out any electrical kit in the trunk - its a right faff of a job slide it on a bit of plastic - like a bag - and disconnect / reconnect the breather pipe elbow on the right side (can be done with battery in place - but not much room
Just gotta put a proper new battery in it. I don't have much else for advice. Start fresh with a fresh battery. Forget everything else.
How can you say "Forget everything else"?
Everything that the OP has posted for me points his starter went out. Before the starter is tested, I say Forget everything else.
And the starter is easy to test. Go under car and connect the main starter cable to the small trigger post and see if it moves. If it is fine, it will crank the engine. I bet in this case it would not.
Everything that the OP has posted for me points his starter went out. Before the starter is tested, I say Forget everything else.
And the starter is easy to test. Go under car and connect the main starter cable to the small trigger post and see if it moves. If it is fine, it will crank the engine. I bet in this case it would not.
Occam's razor. It's the most logical starting point.
By OP’s post he had battery tested and it passed the test. It was fully changed and he says ”nothing” when he tries to start.
If starter/starter solenoid (on starter) goes out you get nothing no matter how good the battery is.
It could also be with other start components but his comment of ”sluggish” starting first indicates that the starting system works and trigger signal to start solenoid is present.
But the simple starter test I explained would very quickly tell how it is. If in this test the starter cranks the engine the problem is somewhere in systems that send the start trigger voltage to the start solenoid at the starter. These systems include the battery, of course. If no crank, replace starter.
OP’s car is an 08 model. If the car has the original starter it is way beyond time to replace it if not replaced at some point already. Heck, car at 17 years is old enough for two starter changes.
My E550 was only about seven years old when its starter had to be replaced.
I'm not saying the starter isn't the problem. But I have a pretty decent amount of experience with dead batteries. I have, many times, metered a battery that showed 12.6V (AGM) on the display but would not turn over the car. A top charge means nothing.
I'm not saying the starter isn't the problem. But I have a pretty decent amount of experience with dead batteries. I have, many times, metered a battery that showed 12.6V (AGM) on the display but would not turn over the car. A top charge means nothing.
If you meant post #15 that still does not convince me. My money is still on the battery. If you're not even hearing the pinion gear solenoid you've got voltage issues.
not had it happen on a car - but modern bike's have this canny mess up where if the battery is low - the electronics will not ask the starter to do anything at all.... never a slow or lazy crank 100% nothing at all on the button.... madness - then you buy a battery and its 100% normal
not saying that fixes a 221 - as people end up replacing starters every other week on some of them...
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