I have a 2008 S550 and have been having some electrical problems. It first started with the airbag light coming on and showing passenger airbag restraint malfunction, the windows would roll down but not up and the fuel gushed would show empty. This would happen randomly. Shortly after the brake light on cluster would do the same. Then my turn signals would stop working and headlights would turn on during the day, as well as engine fan running on high. Then the push button start stopped working, and all cluster lights would stay on with key out. Also it does not start sometimes and exterior temperature shows 185 degrees.

Now everything is pretty much happening together, I have a snap on scanner that is giving me a bunch of can bus codes and I couldn’t communicate with the sam modules front or rear.

It seems to be worse when it is hot outside. I let the car sit for a week and the weather cooled down for a couple of days(70s) and everything seemed to work properly, now it is getting warmer again (90s) it is happening again and getting harder to start.

I’m just trying to get a step in the rite direction of where I should be looking, thanks for any info

 

take a look to see if the Front SAM has been taking a bath - a standard features of mercedes vehicles

the flat bit you see with fuses is not really the SAM, underneath in that bucket amongst the rats nest of wires from hell is a module that might have fried its brain due to water ingress - they are not just plug and play - but if you get the same part number and or one of multitudes of later ones you will get a starting point to play from

the other issue is the batteries, (if the front is a baby one you likely have a huge one everyone ignores hidden in the boot - but a real 2008 should just get a huge one upfront...) these cars can't diagnose faults without the battery going flat doing the tests - they must have battery support whilst working on them

check for water - delete all the codes it just holds tonnes of lies due to low voltage and historical confusion - get the battery / batteries in A1 condition, add a charger and start again...

 

Thank you for the reply, Batteries are good, this one has the smaller one upfront and bigger one in the trunk. I opened the box where I believe the front sam to be on the driver side close to the firewall, but it looks really dry in there. I may try to remove it and see if the board is burnt. I was just not able to communicate with either Sam.

 

Last night the car would not start and I couldn’t get the windows to roll up. This morning I get on and it started up with brake and airbag light on, no turn signals, windows go down but not, no control of a/c, driver door showing open and fuel guage on 0 with no yellow light.

 

you know the 221 has electrics everywhere? might be worth a quick check of the fuses in both ends of the dash

https://www.mercedesmedic.com/merced...gram-location/

if anyone connected a battery back to front, the pre fuse boxes need checking out



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I am just guessing but I think you have problem on the charging side. Please check the serpentine belt for slippage on the alternator. Please fully trickle charge both batteries. BOTUS has written about the best connections to make to charge both batteries. After a full charge, please state the resting voltage of both batteries. You need 12.0 volts or better at rest. Start the car. Take it for a 20 minute drive. Check voltages again. If less than 12.0, your alternator is at fault killing any new batteries you might have had replaced. I am betting you have a failing alternator or a bad pulley or bad tensioner causing the slippage.

But then again, I am just guessing.

 

Thank you guys for the input and replies, front battery is at 13 volts and rear is at 12.8 with car off. I removed front Sam and fuse box and inspected board and everything looks fine, I don’t see any burn marks or water intrusion. I figured since it is an intermittent problem the fuses are most likely ok, but maybe a relay? My next step was to remove the rear sam and see if there is any signs of damage. I have added pictures of the codes it is throwing and the module that are being read, there quite a few modules that are not communicating.

 

Those resting voltages are good. Now start the car and tell us the voltages reported while running. If the alternator is good, you should be 14+ volts running. Report back here. If your voltage is still at 12 while running, the alternator is failing, and as BOTUS often points out, the car will drain the battery in 20 minutes or less without a charger. To protect sub-systems, the car automatically shuts stuff down to try to preserve voltage; but if the charging system is failing, it will simply kill the batteries.

Let us know your running voltage.

 

delete the lot and drive for 10 mins then recheck for a list that might be real

I'd pull up the front passenger side floor mat - it folds back from the firewall to unveil a load of kit on the can bus on an aluminum plate their feet rest upon - check for soggy connections under here (beneath the battery it fills with leaf litter then fills the car up inside)

canbus faults on mercs with a soggy unnoticed puddle beneath the front passenger carpet cause many mercs to give up - they do it on purpose to get older car's off the road

disconnect the batteries before playing fully....

 

After deleting the codes and redoing the code scan these are left, at this time the car will not start. Am I on the rite track by checking the sam modules? Could this just be a can problem? If it is a can problem how do I start my troubleshooting. I’m fairly versed in fixing my own cars and have never had to take them to the dealer, but I’m not sure about this one. I’ve done a lot of research and haven’t found really anything to put me on the rite path to solve these issues. Thank you guys for taking the time to try to help me it is much appreciated and I will definitely post a reply to when I get it figured out. Definitely a when and not an if I hope.

 

I think you are on to something botus by telling me to remove passenger side mat. Seems as if the grommet has popped off and I’m sure has allowed water to intrude.

 

It seems some water got into the air suspension computer so I cleaned it off and reinstalled. Also one of the canbus plugs had some corrosion, so I cleaned that as well. Problem still persists but likely has to do with this water intrusion, I also cleaned the ground. Any other ideas of what I should tackle next.

 

top pic of the circuit board u can't have that join from corrosion - might have popped the board...
canbus works on silly low voltages and pathetic signals, so even the slightest corrosion sends madness around the car
to the right (if LHD car) of the fan blower motor sits the HVAC module this might be damp too...

spend ages disconnecting all multiplugs in and around this area and remake a few times to clean up the connections and use something like ACF50 to help abate corrosion

 

Something like DeOxit might help with the corrosion abatement too.

 

Thank you guys for the reply, I got it to power up and atleast get the windows up. I was messing around with the wires around the area and blower motor kicked on and started working and I was able to start the car. I plan on going through all the plugs tomorrow and see if I can narrow it down. Do you have any tips or maybe a diy for checking canbus voltage?

 

I wouldn't bother trying to measure it - any corrosion anywhere will just contuse everything, just use the time remaking any multiplug connection you can find ( but use something to stop it coming back)
you really need to check for leaf litter under the front battery.... ALL the the rain off the roof and screen drops there and floods the blower motor and under your carpet - take a look at the primordial swamp at both side of the screen drains (that never worked from new)

https://mbworld.org/forums/s-class-w...ml#post8820643

 

This seems like a job for Pine Hollow Auto Diagnostics to throw a scope on the various networks and narrow down to which module is pulling the bus down. That green and brown comb thing is where the various networks come together and can be easily isolated for testing there.

 

checked mine this week - two years older - not so soggy - and inside on my airmatic board it didn't have your furry joined up bits.... so yours definitely got water ingress quite badly

 

Hey guys sorry for the late replies, but I let the car sit for a while and finally got around to digging into it some more. I would sometimes try starting it from driver side with no avail, but would go to passenger side and sit down and it would start. So I decided to remove the passenger seat and look at the can distributor under the seat. After pulling the second connector from the end I was able to start the car and have all functions working properly except the airbag light being on. So everything works now and I am guessing this plug is for the airbag module? I thought I’d see if anyone might know what it is for? But for now I left it unplugged until I can figure out what is exactly it is for.

 

USA cars have a different history regarding airbags because so many refuse to wear seat belts, thus they used to get a much larger, higher capacity set of airbags to try and keep un-belted people from smashing in to the dash and killing themselves. Then as many forget children don't cope well with airbags we now make cars differently. Historically starting in the USA with a weight sensor for large airbags, but nowadays to reduce bad publicity from killing children, lots of vehicles have the weight sensor (on the seat squab) to reduce how successfully the airbags deploy based on the weight on the seat at the point of the crash.

I was just watching a M5 crash repair where the car wouldn't start due to a pyro-fuse blowing as all the airbags had deployed. This cuts the power to the engine deliberately. Thinking about your car and the point you just made (about it starting if sitting in the wrong seat) I can image the weight sensor on the drivers side has failed... its embedded in the hideously expensive seat cover that includes the seat foam....

My car scans for the seat weight sensor module when I use my Autel scanner then jumps passed - as my age euro spec cars don't have this feature. But interestingly when I fitted a new seat cover (as the heated seat failed) I bought a passenger cover from a LHD car for my RHD drivers seat. This had the sensor and wiring for the weight sensor and I have a spare plug on the seat module it would fit too - but deliberately didn't connect as it might just upset things (on my car), - I guess you could likely code out the weight sensor feature with the autel scanner or xentry and re connect that plug ?

As for worrying about the airbag and how it might go off in a crash - we should all worry - takata - basically made airbags worldwide for all cars and went bust a few years back - after struggling with the costs of about 7 million recalls to replace airbags that explode and shrapnel kills the driver and passengers - and with many dodgy governments doing deals with car manufacturers its leaving all the old cars with deadly airbags

Australia just won a case after taking Mercedes to court for deliberately trying to cover up which cars needed the work

https://www.accc.gov.au/media-releas...pulsory-recall

https://recall.mercedes-benz.com.au/


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You have got to be kidding me. The weight sensor is preventing the car from starting? I think there's something else going on. I've started my car before my wife has buckled up. The only thing I've noticed is the passenger airbag message on the instrument cluster and you get the seat belt bong. I've also started my car without sitting down in the driver's seat. Also, how are you starting the car from the passenger seat? You have to depress the brake pedal.

Out of all those codes, the one that would worry me the most is "no voltage to electronic ignition switch". Almost all of your modules need a signal from that in order to power up.

Some Deoxit D5 and a nylon bristle brush will do wonders for your corrosion. You can also spray it directly into unplugged connectors to clean them up.

 

Did you end up Solving this issue?