Mysterious Mercedes Electrical Problems

Recently, we have been working on a Mercedes-Benz with some major and unexplainable electrical issues. The problem started with the Keyless Go feature. The key would unlock the car via the key fob and start by inserting it in the ignition. But Keyless Go stopped working. Push Start or unlock the car by pressing the driver’s door handle, which stopped working. If you pressed the unlock button on the door, the handle of the instrument cluster would state, “Key not recognized.”

Battery Drain

The next problem this car developed was the battery dying when the car was parked for an extended period or parked overnight. It was confirmed that no lights were left on. After further troubleshooting, we noticed a problem with the COMMAND system. Even though it would turn on, it wouldn’t go to sleep. This was confirmed after paying close attention to the head unit. You could still hear the fan working in the back even though the radio/navigation was turned off.

Door Open and Brake Light

The next problem that soon occurred was an unexplained door open warning message on the instrument cluster. As you drive the car, the red warning light will come on, stating the door is open. But all the doors were closed, and the car symbol would not show any door open.

Windshield Wipers Turn On Randomly

The windshield sippers turned on a few times despite no rain. Mercedes has the rain sensor mounted up by the rearview mirror. The sensor can technically fail, but something else is happening here, as you already know.

Climate Control Stopped Working

Another issue this particular car developed was that the climate control would randomly stop working. Other times, the climate control would operate completely normally.

Battery Warning Light 

Next, the battery warning light came on. Yet the car still started without issues. When the battery warning light came on, several other problems were also experienced. This was not the same issue as with “electronics consumers being turned off.”

Park Assist Random Warning

This particular Mercedes is equipped with park assist sensors. The system would start to beep as if you were approaching an object, yet nothing was near the car.

The engine Would not turn off.

Last but not least, the issue with this Mercedes was the engine not turning off when the key was removed from the ignition. While the instrument cluster lights would turn off once you removed the key, the engine would still run. The car would even still respond to the gas pedal input. You may find it hard to believe, but here is a video showing Mercedes that wouldn’t shut off. 

Removing the fuel pump relay turned off the car. It’s not something you want to deal with every time you park your car.

Common Cause: Control Unit or SAM Module

Every time we start seeing random electrical issues, the first guess is to inspect control units and SAM modules. You need a good OBD2 scanner that can read Mercedes-specific codes to perform this step. Something else to investigate is if there is a chance that any parts of the car have been exposed to water recently.

In this case, the first problem that was experienced was with the Keyless Go system. First, we investigate the Keyless Go module in the trunk.

Surprisingly, we noticed water in the spare tire beside the Keyless control unit. Even though there wasn’t much water, the water splashed on the Keyless Go module every time you accelerated.

Removing the plugs from the module showed that the contacts had started to corrode, and water was present at the connection.

This was all caused by the trunk drain plug being clogged. The plug is designed to allow any water to drain. The rubber plug can easily get clogged by dirt and trash.

Removing the Keyless Go module resolved all the mystery issues we were experiencing except the Keyless Go.

You can try to salvage the old module by drying it, but there is no guarantee it will work.

Conclusion

Every time you experience malfunctions simultaneously, there is a good chance a SAM module or control unit is defective. These units don’t fail for no reason. They fail if water or condensation reaches the module or the electrical connections.

Another item you want to check out is the car battery. If the battery is not charged, it can cause several problems, such as the airbag light on, the car being stuck in limp mode, and random warning lights.

What is the Best Scanner to Diagnose SAM Module Problems on Mercedes-Benz?

If you’re experiencing problems with your Mercedes-Benz, the YOUCANIC full system diagnostic scanner can provide invaluable assistance in troubleshooting the issues. By connecting to your car’s onboard computer, the scanner can read fault codes and provide detailed information about any problems with your engine, transmission, brakes, and other systems. Additionally, the scanner can perform diagnostic tests on various systems, such as the ABS, airbag, and steering systems, to help identify the underlying cause of any issues.

In addition to providing diagnostic information, the YOUCANIC scanner can save you time and money on repairs by enabling you to perform simple fixes yourself. For example, if you notice the check engine light on, the scanner can assist you in identifying the problem and determining if it’s a simple issue you can address at home or if you need to take it to a mechanic. This can help you avoid unnecessary trips to the repair shop, saving you both time and money.

Overall, the YOUCANIC full system diagnostic scanner is a powerful tool to help you maintain and troubleshoot your Mercedes-Benz. It’s an excellent investment for both DIY mechanics and professional technicians, as it can assist in diagnosing and resolving even the most complex automotive problems easily, saving you time and money on costly repairs.