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Mercedes SAM – Signal Acquisition Module Explained

What is a Mercedes SAM module

sam unit location repairSAM stands for Signal Acquisition Module. A SAM module (Signal Actuation Module) receives data from sensors, switches, and controllers and can send data, actuate (activate) components, and monitor systems. Mercedes-Benz has been using SAM modules since the mid-90s.

Symptoms of a defective Mercedes SAM unit

center dashboard buyyons dont work bad samThis is a list of a few possible SAM-related problems. All systems on a Mercedes-Benz are controlled via CAN  Bus and SAM units; any issue you may experience could be due to a defective SAM unit.  SAM units don’t frequently fail unless there is water intrusion or other problems.

Here are a few problems caused by a bad SAM unit:

  • Fuel Level / Gauge not working – The sending unit installed in the gas tank records the fuel level. In cars without CAN / SAM, the signal is sent directly to the instrument cluster via two wires. The signal on Mercedes-Benz must be sent to the rear SAM since it is the closest unit in the Controller Area Network. From here, the fuel level data can be sent to the instrument cluster or the engine control unit for computing the remaining distance based on fuel level.
  • Lights are not working – We have seen many Mercedes-Benz where one or a few lights don’t work. It can be that the left or right low beams, fog lights, or turn signals may not work. You should always avoid splicing wires to get power for aftermarket HID lights, alarms, or connecting a trailer hitch.
  • Fuse Keeps Blowing – If you have a fuse that keeps on blowing, it is possible that the SAM module is defective and needs to be replaced.
  • Poor key fob / keyless entry range – The doors’ key lock and unlock signal is transmitted via the rear antenna. The antenna is connected to the rear SAM module, and a short in the wiring can cause damage to the SAM unit. If this is your dilemma, you may notice a blown antenna fuse.  Especially if you replace the fuse and it keeps on blowing. Don’t use a higher ampere rating fuse to try to fix this problem.
  • Battery Drain –  A defective SAM module can cause battery drain when a Mercedes-Benz is parked overnight or for several days. Other possibilities, such as a defective audio gateway unit or a bad power seat motor, should be eliminated.
  • Taillights staying on – If one or both of your tail lights stay on constantly, your rear SAM unit may be defective. Other symptoms of a bad rear SAM include doors showing open all time, even when closed.
  • Center Dashboard Buttons don’t work – Currently, we are working on an S-Class in which all the center buttons ( hazard light, head restraint, AIRMatic switch, etc.) don’t work. In this case, we are not getting any communication with the module, which is most likely an issue with the SAM unit.
  • Mercedes Blowing Only Cold Air – This problem could be caused by a defective front SAM module. Before you replace the front SAM module, check the water valve (the changeover/duo valve) first.

SAM Module Explained

Think of  SAM as the router in your home. All your devices, network printers, phones, and computers (switches, window motors, sensors, etc.) communicate via your router. If you hit print on your PC, the data (signal) gets sent to your network printer via the wireless router (SAM unit). You may also hear the term CAN Bus which stands for Controller Area Network. Think of  CAN Bus as the ethernet cables and wi-fi that make your home network communication possible.

Not all cars have SAM & Controller Area Network. That would be the same as connecting your printer directly to your computer via a USB cable.

Mercedes SAM Module Location, Purpose

location of sam moduleWhere is the SAM module located on a Mercedes-Benz? The location of the SAM module depends on the Mercedes-Benz chassis. The fuse box usually installs most SAM modules. Mercedes-Benz cars may have rear and front SAM modules.

  • Left SAM is located in the engine compartment. It handles left front lights, side lights, a rear air outlet, illumination, glove compartment lock illumination, light switch, steering column adjustment motor group, ESP, SPS, and BAS control, AIRMATIC with ADS control unit, ABC control unit. Left SAM also receives signal data from the left front brake pad contact sensor, A/C pressure sensor, refrigerant temperature sensor, brake fluid indicator,  outside temperature sensor, and parking brake indicator switch. Low beam is handled left SAM.
  • Right SAM is in the engine bay. Handels right, front lights and the side light, center console storage, lights in the glove box and eyeglass compartment, ashtray, and footwell. It also handles pumping for the windshield washer nozzle and pumping water for the Headlamp Cleaning System, the radiator fan for coolant, the fan for the transmission oil cooler, and the circulation pump for the heating system delivery unit. Monitors right front brake pad wear sensor, coolant level indicator with windshield washer fluid level indicator and Anti-Theft Alarm, hood switch. Low beam communication is handled by the right SAM,
  • Rear SAM is typically under the right rear seat. Handles communication with trailer recognition control unit, ESP, SPS, and BAS. It communicates with the overhead control panel. It controls rear lights, closing the trunk and fastening seat belt indications; the fuel tank level sending unit, a tilt sensor Anti-Theft Alarm inclination sensor, door contact switches, and the rear brakes wear sensor. (Source: W220.ee)

Top 4 Problems that cause SAM failure

  • Corrosion – The SAM control module may have gotten wet, corroded, and eventually failed. Typically this is caused because the repair is performed near the SAM control unit. If the SAM modules are not closed and sealed properly, they will eventually corrode. If a SAM module fails due to corrosion, you may first notice intermittent electrical problems.
  • Excessive current draw – SAM control units don’t fail often. Other than physical damage or corrosion, the next most likely cause of making your SAM unit fail is an excessive current draw. If you’ve modified your Mercedes-Benz or have a module drawing too much current, that can damage your SAM unit.
  • Broken wires – Broken wires or shorts can cause your SAM module to fail due to excessive current draw.
  • Incorrect SAM coding – If you just had your MB serviced and have a different problem, there may be a programming issue. During a repair, a technician may have reprogrammed a new sensor but didn’t complete all the needed programming. If this is your situation, t is important to read all fault codes before you start doing any troubleshooting on your Mercedes-Benz.

The #1 problem that causes SAM units to fail is water intrusion (corrosion). 

Don’t be surpprised if you replace your SAM module and a few months later it fails again. Try to find the cause of the problem if you don’t want for the problem to reapear. 

Troubleshooting SAM  Control Unit

mercedes sam unit locationFinding the root of the problem that caused a SAM to fail can be difficult. Finding Mercedes SAM-related problems is not as simple as using a multimeter to check voltage and continuity.

Step 1:

If you have electrical problems, you should always check all the fuses and relays first.

Step 2:

Write down your symptoms and research the problem that you have. Do you notice several problems, such as windows not working, turn signals, fog lights, and fuel gauges?  In cases when the SAM unit is defective, you may see several problems that initially don’t seem related. Replacing your Mercedes SAM unit is more cost-effective than opening it up to narrow it down and fix your existing unit.

Step 3:

best Mercedes Benz obd2 scanner
Next, you should read the fault codes to confirm that the SAM unit is defective. For this, you will need a scanner such as the YOUCANIC scanner. The fault codes will have enough information to tell whether this is a SAM module problem. Note that a generic OBDII code reader cannot pull fault codes from the 40+ control unit and SAM-related fault codes on your Mercedes-Benz.

The following video shows you how to read and clear codes from the Air Bag control unit. You can follow the same procedure to read and clear codes from any module, including Front and Rear SAM. If you have Mercedes-Benz problems, pull the codes from all the control units, not just the SAM module.

Not all control units available for Mercedes-Benz cars will be installed on your Mercedes-Benz. For example, you may not have DISTRONIC PLUS adaptive cruise control on your MB even though that option was available for your model. If you try to connect to the Distronic Plus control unit to read codes, you should get a message that says this module is unavailable.

Replacing a Mercedes SAM unit can be expensive. You should eliminate any other possible issues and get a second opinion before replacing the SAM unit.

No Communication with the SAM module

If you get an error message that no communication with the SAM module exists, the SAM is defective or not getting power.

Where to buy Mercedes SAM Control Unit

Used Mercedes SAM units are affordable and one option if you have an older MB. We have set up custom eBay searches for you to check prices on Mercedes-Benz SAM control units.

Mercedes SAM unit repair

failed mercedes samWhen the Mercedes SAM module fails, the circuit board or the connections often have a short or are corroded. Opening up a SAM unit and trying to repair it yourself is possible. If you notice any corrosion inside the SAM unit, investigate why and how the water got inside your SAM module. You must remove your SAM unit, check it for corrosion and lose contact and clean it carefully. Take pictures of everything when you take your SAM unit apart. Otherwise, you may have a hard time putting it together. If you have the time and patience, you should be able to repair the SAM unit yourself.

Watch the following video on SAM unit DIY repair.

SAM unit repair service

It is viable to send your SAM unit for repair to a specialized shop. They will open your SAM unit, repair it and return it for you. The benefit of a repair service is that you don’t need to do any programming after installing your old SAM.  At the time of this writing, we found a couple of SAM repair services on eBay where you can mail your SAM module and get it back repaired in a few days.

Mercedes SAM Module Programing

If your SAM module is defective, your next question is: Do Mercedes SAM modules need reprogramming

In the early model years, you could replace the SAM unit with a used SAM from another Mercedes-Benz and not worry about any programming. Newer Mercedes-Benz models require SAM module programming, and the new SAM unit must be coded with the Sofware Calibration Number (SCN). You will need to contact the dealer if you need a new SAM. An alternative is to buy a “virgin” SAM module and have a mechanic that has Star Diagnostic perform SCN coding and installation for you.

For example, a W220 S430 SAM module can be swapped with a module from another S-Class and not require any programming. When you replace your SAM with a used module, match the part numbers.

Cost to replace Mercedes SAM module.

The cost to replace a SAM module can vary greatly. Not only does it depend on if it is a front, left, right, or rear SAM. It also depends on the model and, most importantly, if the SAM unit requires reprogramming. Therefore, a defective SAM may cost a few hundred dollars to thousands of dollars to replace.

Is the dealer the only option to get install a new SAM?

If your SAM unit needs to be coded, you must have it programmed. The dealer is not your only option. If you have a mechanic in your area with an authorized MB Star DAS scanner, they can perform SAM module programming and SCN coding.

SAM Service Campaign / Recalls

If you have a new Mercedes-Benz and are having problems that may be related to a defective SAM module, always call the dealer and ask if there are any open service campaigns or recalls. If there are, you may be able to get your Mercedes-Benz repaired for free.

What Scanner Can I Use to Diagnose SAM Module Problems on my Mercedes-Benz?

The YOUCANIC full system diagnostic scanner is an essential tool for Mercedes-Benz owners and technicians looking to troubleshoot problems with their vehicles. This diagnostic scanner can help diagnose issues with the engine, transmission, brakes, airbag, ABS, steering systems, and more by reading and interpreting fault codes stored in the car’s computer system. With this information, you can make informed decisions about repairs and maintenance, saving time and money.

In addition to diagnosing problems, the YOUCANIC scanner can also reset maintenance reminders and service indicators, ensuring that your vehicle is properly maintained and preventing potential issues from occurring in the future. This feature is especially useful for Mercedes-Benz owners who want to stay on their vehicle’s maintenance schedule without visiting a dealership or a mechanic. Overall, the YOUCANIC full system diagnostic scanner is a valuable tool that can help you keep your Mercedes-Benz running smoothly and reliably for years.



  1. Hi! I have a s320cdi 2001 and the battery drains over night, I checked battery it’s good. Do you think it’s SAM unit??

    • Mercedes Medic

      It could be. One system is not going to sleep. Check for a parasitic draw at the fuse box to find out which system.

  2. My headlights, fog lights and taillights will not turn off even when in the 0 position and when the key is out of the ignition. The green fog light indicator will not turn off. I quickly locked and unlocked the doors via the button inside the car and the lighting issues seemed to be connected… I have to disconnect the battery to avoid a deal car.

  3. Spilled water from 5galloon jug in back, I believe SAM module damaged. Turn signals don’t work, rear view camera doesn’t work, satellite radio comes on and goes off when I turn engine off, fans seem very loud when I start car!! Battery seems to barely push correct voltage to starter. ML550 Merc.Benz 2008.

  4. i have a 2002 clk430 w208 and my windows, top, and alarm are not working i was told it is my rear sam? but I cant find it,any help would be nice. i just got the car. The battery was dead. I got the car from a donation action.

  5. hi my name is isaiah i have a 2001 clk430 convertible, i cant find my rear sam? any help on its location would be great

  6. i have a 2001 clk430 convertible, where is my rear sam located? and how do i know if you respond are you going to email me? i found this page just on a google search and might not find it again

  7. hello,i have MB CLK 230k W208 and I have this problem, sometimes work and sometimes do not work 3 options: tilting the rear head restraints, the button on the central locking panel, heating the rear window and the rain sensor, and sometimes when it does not work it turns the janitor on and sometimes the machine itself picks , but sometimes everything works and the rain sensor and all the buttons, and it does not pile, so constantly.

  8. 2006 c230 shop replaced front sam due to secondary air not having power and in tx got to have that t0o get inspected.so maybe u can help me out here they couldnt et start after replacing so told me had to go to dealer to get programmed so i did only codes i have had on car is due to secondary air and esp absthey told me they got it programmed but it no crank and 450 to run diagnostics on it to find out what wrong with it.so i tow home .told tow dr i bet it is loose neg battery cable sure nuff so loose u could free move it and even wiggle it up and down tighten it up also noticed that my ols sam has two fuses thar i didnt see in this new one so i filled the slots .2 min later car started right up.so i didnt try to start befor i put the fuses in it may just been loose cable but it was fuse 53 and 54 .now is a overwhelming number of faults i never had befor they day they programmed front sam it will start once then not even click then it may start and be able to go into gear but dead electronics and insterment cluster key stopped unlocking doors but would still ingauge in ignition again start or not start but move to start and all the liht go off on dash and just a click or it start and as fast as it start no cluster no dash no steering stuff.my battery charge then next day down to 12.2 or 12volt got message from every test moduler no can message sent or recieved .which is because of the dead dash now my scan on the eis show no faults .in datastreem if my dr door open it say closed and my pass door is closed it will say open it say turn signals deactivated but they work then it tells me that it is right hand drive park brake off it say it on i got circuit 15 and 15 r not ok now pausability error in rear sam. is it possible that the front sam isnt programmed coded correctly .(i put my old sam back in car and ran all the dignostic and it was back to it old self no key problems at all start every time lefthand steerin turn signal active park brake off when off door open when door open no 15 or 15r codes only codes is esp/abs which is anothe qustion .but put new sam back in car and chaos with can messaes and key working battery drain .. can the sam be programmed properly if the battery doesnt have at least a constine good voltage all the codes that was on car esp abs was still on car when i picked it up along with all the other new ones do the new front sam.does the car not need to be cleeared from all codes to programnew sam. even if they come right back after starting car at least clear while programming so no coruption files get into the new sam .in my mind car couldnt have went from the esp mod.code which i replaced as well to getting car back starting it and every moduler and rear sam and eis all bad or going bad then they not bad when old sam back in car .maybe new sam misprogrammed and got the can eis confused and not letting it go to sleep .need help so i can get it took care of.if i have to take it back to dealer because of these i hope they will know that it is a free trip for me on them .sorry not good writer

  9. 2000 Merecedes E430 — problem wiper does not work, replaced motor and front SAM. Both original & replacement SAM modules, relays click. Notice there is nothing connecting M6 & M8.

  10. I have a 2006 c350 that keeps blowing fuse 53, when I replace the fuse it blow’s when I turn the key to position 2. Can’t pull a proper code with out power only gives a p0606 was getting a mirror turn signal fault at one time but it when away. Is this the sign of a bad front Sam?

    • You have a short that can be hard to find. Yes, you most likely won’t get a code. A multimeter may come in handy in this case.

  11. Ok, I don’t even know where to start when it comes to Phantom codes that I’ve gotten from my 02 s430. I will try and list them all if I can remember correctly:
    1 Mirror left turn signal out ( spiratically works and doesn’t work for periods of time)
    2 ^same for mirror right turn signal
    3 steering collum sometimes will not adjust up and down when trying to move the lever.
    4 passenger seat movement button sometimes act wacky ( press to slide back and moves forward)
    4 Check engine fault codes come up but after resetting the same codes never appear twice ( after a month of making notes of fault codes and clearing them)
    5 When raining hard dashboard light sometimes flicker and headlights will act weird/wiper blades won’t move for a period of time
    6 One time o2 sensors read that there was no signal but then worked the next day
    7 Display defective visit workshop came on for about 2 days then never seen it again
    8 Srs light flickers but goes away when someone sits in passenger seat
    9 Abs light stays on and cannot tell from scanner what is causing it

    ok with that being said I am about 90% sure that this is an electrical issue somewhere and I don’t even know where to begin looking.

  12. I think I am having issues with my SAM unit, I have a 2012 Viano W639 with the following issues that may or may not be related.

    1. Reversing lights come on and go off immediately (Warning on dash say reversing lights comes on). My mechanic says the system is showing a short circuit.
    2. When lights are on a warning comes up saying number plate light (both working correctly with new bulbs).
    3. Tailgate doesn’t always unlock with rest of central locking.
    4. Reversing camera shows black screen when in reverse.
    5. Headlamps don’t auto level as they should.
    6. Auto wipers don’t seem to react as quickly as they used to.

  13. connected battery for c240 reversed headlights remain on starts but when one terminal is removed stops the engine

  14. I have a 2002 clk320. I was driving and it just stopped running. I had to have it towed to a repair shop. He thinks it the sam module. The car started every time he tried. I drove the car home and it died in the drive way. I waited about an hour and it started so I was able to park it under the car port. But the check engine light came on. Do you have any advice? The repair shop wanted to charge $600 for a repair kit for the sam module. He does not have a scanner to make sure that is in fact the problem..

  15. I have a 2009 ML320 and about a month ago my headlights stopped working, low beam, high beam, marker light on the LH side and front turn signal on the LH side. The RH side marker and turn signal works but no headlight. I checked the power going to the low beam and high beam both have power. No power on the marker and turn signal on the LH side and there is power on the marker and turn signal on the RH side. After reading your article could it be the SAM gone bad? Last year during the summer i was also having random problems with the air conditioning, sometimes it worked and sometimes did not, but this year no problem with the air and i havent done anything to it, i also noticed that there is hesitation between gears, brake wear light comes on randomly even after new brake pads and sensor were installed, check engine light comes on and off randomly I took it to the dealer and they could not figure out the headlights, they used some repair kit for my RH brake light and rewired it as It was also not working they changed the air intake as they tought this was causing the hesitation because they found a small crack but i still get the hesitation, no stored codes for the check engine light were found.
    Please help

  16. Mine is 2008 GL450.

    The sysmptom is constant battery draw. After many days, they came up with SAM. They didn’t talk about which SAM is bad like left/right? How much is the approx. cost

    Thank you

  17. I have a vito sir light blinks no fault codes fault started on after a faulty alternator was replaced by a garage

  18. My 2011 Sl350 required a new front battery A$780 I drove the car for 80km Started car in the morning red battery light came on suggesting battery not charging. Mercedes Benz dealer found that front SAM was faulty. Cost of replacement A$2900 including A$780 for labour. My question is when the new battery was installed the vechile required re programming, could this have caused the SAM malfunction if re programmed incorrectly
    Any comments welcome

    • Hi Terry,
      We don’t think that the programming caused the SAM malfunction. Even if the programming was done incorrectly they should have been able to go and change it. This is just a coincidence of both problems happening within days.

  19. I just recently purchased a used 2008 ML350. Very well kept inside and out. However, haven’t made the 2nd pymt and electronics seemed to go out. Passed the 30 day warranty. Took to mechanic that specializes in electric and electrical issues in cars and was told that the rear SAM needs to be replaced. $950 but as a ‘courtesy’ and favor to the dealer will reduce to $600 however said can not guarantee that this will fix the trunk hatch. Does this sound like a good deal?

  20. Hello,

    I have a Mercedes C230 Kompressor 2000 W202 4cyl and had my battery die on me. Once I replaced the battery, the following issues occurred:
    -no turn signals
    -no windshield wiper
    -no horn
    -no rear defrost
    -other miscellaneous issues

    From reading this article, it seems that there may be an issue with the SAM unit. Is it possible that faulty relay’s could be the issue, or are there too many problems for this all to be caused by a faulty relay? Thank you for the article and for any advice/assistance you can provide.

    • Anything is possible in these cars but the replays typically control one or two circuits. You have too many things going on.

    • HELLO,
      i have the same car model , year and problems like you . If is posible to you to tell me what solution you found it will be really appreciated.
      THANK YOU!

  21. mercedes w220 s500L 2002, the immobliser and center console and brakelights all gone don`t know why what can I do to repair them, is SAM module or ecu module, the engine turns on and only these three don`t work and I can not shift the gear from park anyone knows what do I have to do?

    • You need to have someone with MB Star Diagnostic troubleshoot your SL. It is possible that the SAM module is the problem but you need to be sure before you start replacing parts.

  22. My S500 started to randomly show side light as defective and it turned out to be the SAM unit.

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