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Mercedes SAM – Signal Acquisition Module Explained

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What is a Mercedes SAM module

sam unit location repairSAM stands for Signal Acquisition Module. A SAM module (also called 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, and any issue that you may experience could very well 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. On Mercedes-Benz, the signal has to be sent to the rear SAM since it is the closest unit in the Controller Are Network. From here the fuel level data can be sent to the instrument cluster or the engine control unit for computing remaining distance based on fuel level.
  • Lights 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, alarm 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 key lock and unlock signal for the doors 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 should be eliminated such as a defective audio gateway unit or a bad power seat motor.
  • Taillights staying on – If one or both of your tail lights stay on all the time it is possible that your rear SAM unit is defective. Other symptoms of a bad rear SAM include doors showing open all time, even when the doors are 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 most likely is 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, also check (changeover/duo valve) water valve first.

SAM Module Explained

Think of  SAM as the router in your home. All your devices network printers, phones, computers (switches, window motors, sensors, etc) communicate with each other via your router. If you hit print on your PC, the data (signal) gets sends 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 that ethernet cables and wi-fi that make up 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 SAM module located on a Mercedes-Benz? The location of the SAM module depends on the Mercedes-Benz chassis. Most SAM modules are usually installed by the fuse box. Mercedes-Benz cars may have a rear and front SAM module.

  • Left SAM in located in engine compartment. It handles left front lights, side light, 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, radiator fan for coolant, the fan for 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. Handels 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 fasten seat belts indications; 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 –  It is possible that the SAM control module may have gotten wet, corroded and eventually failed. Typically this is caused because repair is performed in 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, at first you may notice that electrical problems are intermittent.
  • Excessive current draw – SAM control units don’t fail often. Other than physical damage or corrosion the next most likely cause to make your SAM unit fail is an excessive current draw. If you’ve done modifications to your Mercedes-Benz or have a module that is 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 now you have a different problem it is possible that there is a programming issue. During a repair a technician may have reprogramed a new sensor but they 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 are having 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, fuel gauge.  In cases when the SAM unit is defective you may see several problems that at first don’t seem related. Just replacing your Mercedes SAM unit is more cost effective than opening it up to narrow it down and fix your existing unit.

Step 3:
Next to confirm that the SAM unit is defective you should read the fault codes. For this you will need to see a mechanic that has Mercedes Star Diagnostic or use a scanner such as iCarsoft MB II. The fault codes will have enough information to tell you if this is a SAM module problem or not. Note that a generic OBDII code reader is not able to 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 are having Mercedes-Benz problems, make sure to pull the codes from all the control units not just from the SAM module.

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Note that 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 not available.

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

No Communication with SAM module

If you get an error message that no communication with the SAM module exists, it means that the SAM is defective or it is 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 Mercedes SAM module fails, often the circuit board or the connections have a short or are corroded. It is possible to open up a SAM unit and try to repair it yourself. If you notice any corrosion inside the SAM unit, you should investigate to determine why and how the water got inside your SAM module. You will need to remove your SAM unit check it for corrosion, loose 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 using a repair service is that you don’t need to do any programming after you install 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 would be: Do Mercedes SAM modules need to be reprogrammed? 

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 will need to 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, make sure to 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 from a few hundred dollars to thousands of dollars to be replaced.

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

If your SAM unit needs to be coded, you will need to have it programmed. The dealer is not your only option. If you have a mechanic in your area that has an authorized MB Star DAS scanner, they will be able to 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 is any open service campains or recall. If there are, you may be able to get your Mercedes-Benz repaired for free.

3 comments

  1. 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.

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

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