- Mercedes-Benz C-Class: How to Jump Start Mercedes-Benz (and W205)
Step by step instructions for do-it-yourself repairs
Browse all: Specifications and General Maintenance
List of faults that occur after disconnecting battery...
Last edited by norteno; Mar 29, 2020 at 06:35 PM. Reason: left a word out
.
.
Last edited by MissKhris90; Sep 9, 2020 at 10:33 AM.
https://www.google.com/search?q=w164+front+sam+mbworld
See if you can resurrect one of the threads there.
The typical battery disconnect sequence is always NEGATIVE then positive...
You may have fried the front SAM module by the symptoms.
The Best of Mercedes & AMG
When i put the car in reverse, the trunk lid pop out, but the reverse assistant antennas dont come out.
when i put the car in drive the trunk lid go inside again.
i never replace this pump, so the hoses are in the right places.
This start to happen after the battery died.

When i put the car in reverse, the trunk lid pop out, but the reverse assistant antennas dont come out.
when i put the car in drive the trunk lid go inside again.
i never replace this pump, so the hoses are in the right places.
This start to happen after the battery died.
Parked vehicle in garage about 8 months ago and found battery dead. Hooked up battery charger and immediately the fog lights and tail lights started flashing.
Disconnected battery charger and jumped online and read all sorts of do's and dont's and consequential related issues.
Please could I ask some advice on my next move? Greatly appreciated!!
Sounds like maybe the alarm? Although why the siren did not go off is weird.
When I used to disconnect the battery for >1month storage I would unlock the driver door, disconnect negative terminal, and then lock the door using the metal key.
If the alarm was armed as battery died, perhaps when you "re-connected" the battery/charger the alarm went nuts.
Maybe try to disconnect the battery (just the Negative terminal) and charge it for a few hours, then connect back the Negative and see what happens. Try to "unlock" the car from the keyfob if it keeps flashing..
Really appreciate your suggestions. Will definitely give that a try tomorrow.
Was thinking the battery may be done as well, do you think if I disconnected it and took it to get tested I may have more issues?
Again appreciate the help!
Kind regards
Everyone who keeps their car long enough will eventually have to disconnect an old battery to replace it with a new one. Given the emergency nature of dead batteries when you least expect it, a dealer with expertise may not always be handy, either. So, it would probably help to identify what can happen, and the fixes you have found to correct them.
If we get enough responses to these, I will make this a sticky thread so all of us can find it in the future. So please share your experiences here. Thanks.
Many thanks for your suggestion of removing the negative lead while charging. The charger is doing it’s thing now without the flashing fog and tail lights.
More to follow after reconnecting when the charge is complete.
Thanks again
Kind regards
1st I have not done this with my newer Mercedes however I have done this with many other vehicles on the farm.
I swap batteries around all the time from trucks one truck to dump truck for example or from tractors to truck etc and I do it leaving them running.
As well as cars.
I also did do this with my older Mercedes M series.
never effected them to leave engine running and switch batteries around.
1st I have not done this with my newer Mercedes however I have done this with many other vehicles on the farm.
I swap batteries around all the time from trucks one truck to dump truck for example or from tractors to truck etc and I do it leaving them running.
As well as cars.
I also did do this with my older Mercedes M series.
never effected them to leave engine running and switch batteries around.
You should NEVER disconnect a battery cable while engine is running .. It causes a electrical surge that will damage modules ,components ,bulbs .I have seen every bulb in a vehicle get bright then burn
out when a guy disconnects a battery cable while engine is running.I have seen modules ,processors .elect components go bad also. If you havent damaged something on your vehicle doing this ,be thankful
and dont do it again .I worked as a Senior Master gas and diesel vehicles for forty years at dealership ,now retired ,have seen many vehicles towed for this and the damage can be extensive / expensive.
When doing any diagnosis use the procedures in the vehicle shop manual with tech bulletins with updates. The elect system isnt designed for it .I have seen repair bills as high as $9,000.00 . If you doing
work on your own vehicle invest in shop manuals ,of course tools.A shop manual is like having a senior master tech helping you.Its not easy to quote someone with brand new vehicle four or five grand to
replace every single bulb on their vehicle because a cable was removed while engine is running.The alternators get the diodes ,capacitors,volt limiter damaged the volt surge does the damage.Also when
you disconnect either cable when its running there is a noticeable spark that will ignite excessive acid fumes and will explode ,then you have a two piece battery.Of course you wont know it untill you wash
the battery acid from your face and eyes and your ears stop ringing from the explosion.
I guess your 40 years of working on cars undoes my 40 years of doing it hahhahaha
Look Not only have I worked on cars for as many decades (yes professionally) but I also live in a solar home.
trust me I know batteries and battery charging.
This issue like so many has people who have no clue what they're talking about chiming in often as in your case with pastes from something they look up.
Again I have done this 1000s of times without exaggeration.
in fact I'm thinking of making a video to prove the point.
It's a myth that you cannot disconnect a battery from a running vehicle UNLESS that vehicle has a system in place that would make it an issue.
I do this ALL THE TIME.
Again I am constantly swapping batteries around using vehicles as a charger for low voltage batteries on my home etc.
Again I havent done it with my GLK Mercedes which I have two.
But did do it with the two ML series I had as well as Porsche, BMW, Volvo and SAABs back in the day
Not to mention all the fords, chevys, dodge vehicles too and Toyota etc.
I have done this a lot.
A........LOT.....
As for "spark" exploding a battery sorry but spark can happen anytime you hook up a battery wrong.
If your getting "spark" when you connect a battery you are connecting it WRONG
(Not very good for a guy with 40 years real experience) you have to connect the positive first. Then the negative and wala NO SPARK.
But if you hook up the negative first then positive it will spark.
as for the "electrical surge"
Also a load of crap.
Your alternator puts out power at its rate via RPMS.
It doesnt put out MORE power because the battery is disconnected.
The FACT is when your engine is running it is running on the alternator and the voltage regulator controls the voltage regardless of the battery.
A bad battery can certainly be a DRAIN on the system but no battery doesnt make MORE voltage that's also BS.
The votage is what the voltage is based on what the voltage regulator puts ot to.
Not Based on the battery
A the battery does is start the vehicle and that's it.
It is not the power source of the vehicle just a storage unit of power for a TEMPORARY call of power to the starter to get the engine going.
once it's running it runs on the alternator
NOT the battery.
Again depending on the vehicle the battery can be pretty monitored and if your vehicle detects a fault in the circuit it throws a light, but the vehicle can and will run even with a dead battery so long as your alternator is good.
QUOTE=yaknart33;8603810]You should NEVER disconnect a battery cable while engine is running .. It causes a electrical surge that will damage modules ,components ,bulbs .I have seen every bulb in a vehicle get bright then burn
out when a guy disconnects a battery cable while engine is running.I have seen modules ,processors .elect components go bad also. If you havent damaged something on your vehicle doing this ,be thankful
and dont do it again .I worked as a Senior Master gas and diesel vehicles for forty years at dealership ,now retired ,have seen many vehicles towed for this and the damage can be extensive / expensive.
When doing any diagnosis use the procedures in the vehicle shop manual with tech bulletins with updates. The elect system isnt designed for it .I have seen repair bills as high as $9,000.00 . If you doing
work on your own vehicle invest in shop manuals ,of course tools.A shop manual is like having a senior master tech helping you.Its not easy to quote someone with brand new vehicle four or five grand to
replace every single bulb on their vehicle because a cable was removed while engine is running.The alternators get the diodes ,capacitors,volt limiter damaged the volt surge does the damage.Also when
you disconnect either cable when its running there is a noticeable spark that will ignite excessive acid fumes and will explode ,then you have a two piece battery.Of course you wont know it untill you wash
the battery acid from your face and eyes and your ears stop ringing from the explosion.[/QUOTE]
with a engine .Engines running on gas ,diesel ,lpg ,propane ,hybrids,elect,even flying car conversions .It seems that you think being a trained certified tech and the info
I have posted is just some cut and paste b s from an article I read you are mistaken.I only share what I know from training and hands on experience.Anyone with basic
training knows you dont disconnect pos cable then the neg cable .Neg cable gets removed first then pos cable .With ground side actuators components you are asking
for problems .Even then if there is any load you will get a spark . With modules ,on board diagnostics this is recipe for problems . The number of vehicles I have
repaired from back yard mechanics over the years because they knew more then trained tech has paid for many things for my family . To post info that is incorrect like
your "myth" of disconnecting batt cable with engine running is incorrect. I usually dont post much because people like you that think they are right and trained
experienced techs are wrong ,you are the person that can fix anything ,but can you fix it without creating other concerns? Your take on alternators is wrong when the
alt has diodes,capacitors that limit voltage/amps often an internal volt regulator. Its not unusual to see ,at idle,it putting out 20 plus volts 100 plus amps after
disconnecting batt cable when running ,it would have a direct short as well.
I would like to see your self taught repair videos ,it would be like "Primitive Pete" . Hes the guy your high school auto shop taught you not to emulate ,uses diagnostic
dice ,wrong tools ends up doing more harm then good. Of course the diagnostic dice you roll them and repair what it says then try again ,rinse and repeat. Make your
video I could use some humor . For those that want to do repairs on your own cars do not follow this guys lead he has no clue .Get shop manual read it follow it ,you
will be way ahead of the game . I will be waiting for your video ,in meantime you can pick up some Petersons repair manuals ,look at the credits you will see my name
in most of them as I was one of guys that put it together starting back in early seventies. You Fact on engine running on alt without battery is untrue ,how can a PCM
that requires minimum voltage of 6-9 volts and a max of 15-16 volts going to operate with diodes and capacitors burned out and the alt heating up to melt all the solder
joints in alt. Have you ever overhauled a alt,starter,master cylinder? Batteries wont cause a drain on the system but they can have shorted or dead cell that affects
it,drains are from a component or system. The bad part of your post is its so incorrect someone will try it and get hurt or damage his car .
but the main complaints I hear from noobies after re-connecting a battery is
re-sync of the windows & sunroof / panoroofs.
maybe Dean (Scorchie), Steve (MBenzNL), & Sunil (SunMan) could shed some more light on what really happens when you disconnect the battery.....
Carlos

Saprissa@aol.com
If your getting "spark" when you connect a battery you are connecting it WRONG
(Not very good for a guy with 40 years real experience) you have to connect the positive first. Then the negative and wala NO SPARK.
But if you hook up the negative first then positive it will spark.
Anxiously awaiting answer from internet expert. ... no wait, i think I know. If you have anything drawing a load from the battery, (ie a dome light, etc) then you WILL get a spark when connecting the positive terminal first and then the negative terminal. And you dont need the key in the ignition to trigger the dome light, you just have to have the door open.
1) many people mentioned that the rear sam (the one in the trunk for a w203) is easily fried, either complete failure or partial failure of some of the equipment the rear sam provides power to. How does one troubleshoot the rear sam? The only way I see this as possible is by testing each relay and fuse in the rear sam. Can the rear sam still fail if all relays and fuses check out ok?
2) a MB certified mechanic posted that the rear sam failures are almost always related to ~pre~ facelift w203's. What year is he referring to as "pre" facelift and what all did the facelift consist of?
1) many people mentioned that the rear sam (the one in the trunk for a w203) is easily fried, either complete failure or partial failure of some of the equipment the rear sam provides power to. How does one troubleshoot the rear sam? The only way I see this as possible is by testing each relay and fuse in the rear sam. Can the rear sam still fail if all relays and fuses check out ok?
2) a MB certified mechanic posted that the rear sam failures are almost always related to ~pre~ facelift w203's. What year is he referring to as "pre" facelift and what all did the facelift consist of?
I just went through a hell with the supposed it's the rear SAM module, replace it theory. I was working in the dash installing a camera, and shorted something. All the elements of rear SAM were there; no high beams, no dash, no steering wheel controls, no reverse lights, brake lights, etc., so it had to be the rear SAM. Ordered a replacement, knowing it'd have to be programmed. Also ordered a $500 Autel from Amazon, claiming it could program. Nope, it couldn't, but it also couldn't read the front or rear SAM. So I took it to an indy dealer, and they couldn't see either SAM either. Looked at the wiring diagrams, and there's a CANbus line that connects the front distributor and the door distributors together on a daisy chain, and after replacing one distributor that controlled the rear SAM, I took it back to the indy, having put the original SAM back in. As I had feared, it was a short on that daisy chained line, but in the end it was an hour of labor and a diagnosis and $240.
I sent the Autel back, as I had another code reader, but a lot of those hand held code readers only tell you the code issue, not faults or read the SAMs. I was worried I was looking at a much higer bill.
If the SAM is bad, replacing a bunch of fuses and relays is only going to make you angry. I got my second hand repalcement on eBay for like $60, moved everything over, and still had the issue. Was able to send it back minus $15 for shipping. But I'd look for a reputable indy mechanic and see if they can read either SAM, front or rear.
Last edited by chernabog915; Dec 18, 2023 at 11:51 PM.








