The fault code P0108 in a Mercedes-Benz indicates an issue with the Manifold Absolute Pressure (MAP) sensor, also referred to as sensor B28.

The fault code P0108 in a Mercedes-Benz indicates an issue with the Manifold Absolute Pressure (MAP) sensor, also referred to as sensor B28. Specifically, it points to a "Short circuit to positive or open circuit" in the sensor's circuitry. Here are the steps to diagnose and potentially resolve this issue:

1. **Inspect Wiring and Connectors:** Start by visually inspecting the wiring harness and connectors related to the MAP sensor (B28). Look for any damaged or frayed wires, loose or corroded connectors, or any signs of physical damage.

2. **Check the MAP Sensor:** Examine the MAP sensor itself and its connections. Ensure that the sensor is securely connected and that the wiring leading to the sensor is in good condition. If the sensor or its wiring is damaged, it may need to be replaced.

3. **Clear Fault Code:** After conducting the visual inspection and addressing any identified issues, use an OBD-II scanner or a Mercedes-Benz diagnostic tool to clear the fault code (P0108). This will reset the system and turn off the Check Engine Light if the issue has been resolved.

4. **Test the MAP Sensor:** If the fault code reappears after clearing it, you should perform further testing on the MAP sensor (B28). This involves testing the sensor's resistance, voltage readings, and functionality to ensure it is within the specified range.

5. **Check for Vacuum Leaks:** MAP sensors measure manifold pressure, and vacuum leaks can affect their readings. Inspect the vacuum lines and intake system for leaks or loose connections.

6. **Inspect the Air Filter:** A clogged or dirty air filter can affect the MAP sensor's readings. Check and replace the air filter if necessary.

7. **Check the Wiring Harness:** Carefully inspect the entire wiring harness that connects to the MAP sensor, especially in areas where it may come into contact with moving or hot engine components. Look for signs of damage or chafing.

8. **Inspect the Intake Manifold:** If there are issues with the intake manifold, such as leaks or cracks, it can affect the MAP sensor's readings. Inspect the intake manifold for any visible issues.

9. **Replace the MAP Sensor:** If the sensor itself is found to be faulty during testing, you may need to replace it. Use a genuine Mercedes-Benz replacement sensor for compatibility and reliability.

10. **Professional Assistance:** If you are unable to diagnose or resolve the issue on your own, or if the problem persists after inspection and basic maintenance, it's advisable to seek assistance from a qualified Mercedes-Benz technician or mechanic. They have the specialized knowledge and equipment needed for in-depth diagnostics and repairs.

Addressing a P0108 fault code is important, as it can impact the vehicle's engine performance and fuel efficiency. Additionally, always consult your vehicle's service manual or repair documentation for model-specific guidance, as the exact location and specifications of the MAP sensor can vary between Mercedes-Benz models.