Mercedes SAM – Signal Acquisition Module Explained

What is a Mercedes SAM module

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SAM 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

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This 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

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Where 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

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• 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

Finding 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:

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

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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.

• C- Class SAM Control Module C230 C240 C320  W203 W204 (eBay link)
• E-Class SAM Control Module E320 E350 E500 W210 W211 W212 (eBay link)
• S-Class SAM Control Module  S320 S430 S350 S500 S600 CL500 W220 W221 (eBay link)
• ML-Class SAM Control Module ML320 ML350 (eBay link)

Mercedes SAM unit repair

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When 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 Unit Repair Service (eBay link)

Mercedes SAM Module Programing

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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.

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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

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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.