The Mercedes-Benz Tire Pressure Monitor System (TPMS) is an important safety feature that alerts the driver when the tire pressure is too low. The “Tire Pressure Monitor Inoperative” error message can appear on the dashboard if the system is not working properly. The causes of this issue can vary, but some of the most common causes include: failed or malfunctioning tire pressure sensors, damaged or corroded wiring connections, a faulty control module, software issues, or other mechanical problems such as a malfunctioning steering angle sensor or worn suspension components.
Additionally, issues with the valve stems or the tires themselves can cause the TPMS to malfunction and the inoperative message to appear. It’s important to diagnose the problem with a professional technician and get the system checked and fixed as soon as possible, as driving with under-inflated tires can lead to poor handling, increased tire wear, and even a blowout.
Has your Mercedes-Benz recently surprised you with a ‘Tire Pressure Monitor Inoperative’ warning message on its central display? Because of its relatively self-explanatory meaning, it is easy to conclude this has something to do with low tire pressure.
At first, you may think Tire Pressure Inoperative warning is caused by low tire pressure, but that is not always the issue. This article will teach you how the TPMS system works and common problems that may cause trigger messages.
What does TPMS warning message mean on a Mercedes-Benz?
The TPMS (Tire Pressure Monitoring System) warning message on a Mercedes-Benz indicates a problem with the system, and the tire pressure is not being monitored correctly. The warning message is typically displayed on the dashboard or instrument cluster and can take various forms depending on the specific model and year of the vehicle.
The TPMS system uses sensors installed in each wheel to measure the air pressure in the tires and compares it to the recommended pressure levels for the vehicle. If the system detects that one or more tires are under-inflated, it will trigger a warning message on the dashboard to alert the driver. The message will typically include an indicator light, such as an exclamation point, or an image of a tire with an exclamation point. It may also display the specific tire(s) that are under-inflated.
Several issues, including a malfunctioning tire pressure sensor, a damaged or corroded sensor, a faulty control module, software issues, or other mechanical problems, such as a malfunctioning steering angle sensor or worn suspension components, can cause the warning message.
It’s important to address this warning message as soon as possible, as driving with under-inflated tires can lead to poor handling, increased tire wear, and even a blowout. A technician can diagnose and fix the problem by scanning the TPMS control unit using a Mercedes-Benz scanner. It’s also recommended to regularly check your tire pressure to ensure it is at the recommended level per the vehicle’s manual.
These values vary depending on tire size and current vehicle loads, and drivers can find the recommended tire pressure by looking at the sticker on the frame of the driver’s door.
Things like punctures and temperature changes may affect the tire pressure and cause it to drop while driving. Many drivers will not notice this and continue their trip, damaging the tire or even leading to a crash. To prevent this, all 2000 and newer Mercedes-Benz cars have a series of sensors to monitor the pressure in all four tires. The TPMS system will warn the driver if they are under or overinflated.
However, if any of the components malfunctions, it will not monitor tire pressure anymore. When that happens in a Mercedes-Benz, it will warn the driver with a ‘Tire Pressure Monitor Inoperative’ message on the instrument cluster.
The tire pressure monitor is a relatively simple assembly with several components, which makes diagnosing eventual failures easier. These are the most likely causes, although this may differ depending on the Mercedes-Benz year and model.
Missing wheel sensors
Swapping between tire sets is one of the most common situations after the Tire Pressure Monitor becomes inoperative. Many owners have separate sets of summer and winter tires, each with its sensor. After each wheel change, it is necessary to reset the tire pressure monitor, during which the car will recognize new sensors.
A sensor within each tire measures pressure and transmits that data to a corresponding control module. These sensors use a lithium-ion battery as a source of electrical power, which goes flat over time. In most cases, original batteries can last up to 10 years. Another possibility is mechanical damage, which can happen during tire fitment. The easiest way of solving this issue is using a wireless reader, which verifies if the sensor emits a signal.
Blown fuse / Bad Module
Simple as it may sound, a blown TPMS fuse is one of the likely causes here. Depending on the model, the fuse is either located in the rear SAM control module or below the passenger seat. The SAM control module can sometimes malfunction, resulting in TPMS warnings and electrical shorts.
The tire pressure sensor control module is likely faulty, with everything else ruled out. This happens primarily because of moisture, which causes corrosion and produces electrical shorts.
How do you reset TPMS in a Mercedes-Benz?
Mercedes-Benz tire pressure warning resets automatically as soon as you inflate the tires to the recommended pressure. The recommended pressure can be found on the sticker on the driver’s door or behind the fuel door next to the fuel cap.
By resetting the Tire Pressure Monitor system, you will set the current tire pressure in your Mercedes-Benz as a reference value. This is why you should check each wheel’s pressure to ensure it matches the factory-recommended one.
- With tire pressures checked and adjusted, enter the vehicle and turn on the ignition.
- Press the ‘Home’ button on the steering wheel to enter the main display menu. Inside it, use the arrow buttons to navigate toward the ‘Service’ menu.
- Click OK to enter the ‘Service’ menu, select ‘Tire Pressure,’ and then click OK again to initiate the restart process.
- Before restarting, the system will ask you if the tire pressure is correct. You will do this by navigating to the ‘Yes’ option and selecting it with the OK button.
- A ‘Tire pressure monitor restarted’ message on the central display will tell you the procedure was carried out successfully.
Mercedes-Benz TPMS not working
After diagnosing a faulty sensor, which a flat battery or mechanical damage could cause, you will need to replace it.
However, removing the tire from the rim involves the sensor inside the wheel itself. This requires specialized tools and equipment, so you may consider leaving this job to the tire shop. If you wish to do it yourself, there is a method that only requires essential tools.
- Start by removing the wheel in the vehicle question and placing it on the ground with the outer side facing upwards.
- Release all air from the wheel.
- Use a suitable wooden lath as a lever to separate the tire from the rim.
- Move the tire inward as much as possible to access the pressure sensor.
- Using a ratchet with a suitable socket, undo the nut that holds the valve/sensor assembly.
- Pull the valve/sensor assembly from the rim and replace it with a new one.
- Refit everything back in reverse order of removal.
How to Disable TPMS on a Mercedes-Benz
The TPMS is coded in two modules. Instrument clusters and central gateway (CGW). To disable TPMS, you must carry out variant coding on both modules. Disabling or coding the TPMS may be illegal in certain countries.
The Tire pressure monitor will show in the variant coding as item 44, unique equipment code 475, known as Tire Pressure Monitor or Tire Pressure Loss Warner with Position Related Pressure Values.
We hope you find the Mercedes-Benz Tire Pressure Monitor Inoperative Meaning & Problems guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.