This post is also added to the CAMERA STUFF section for future reference.

The hidden menu on the Leica M9, accessed through a specific sequence of button presses, reveals several advanced functions and information that are not available in the standard menu. Here are some of the key features you can find in this hidden menu like sensor type and shutter count.
Some are beneficial to know, and a warning of not touching the others.

Why do I inform you about functions you shouldn’t touch? Simply because they appear when the menu is open for important information.

Should these functions have been hidden better? Surely, but they are there and that’s why I describe them to avoid mistakes.

How do you find the information in the camera?

To know the shutter count and if the sensor is new and doesn’t have the well-known corrosion error issue (read more about it here).

Power on your Leica M9.

Activate by taking these actions: Push the delete button -> up (2x) -> down (4x) -> left (3x) -> right (3x) -> Info.

Then select (SET button) on hardware IDS and check the CCD ID number.

If you have 15 or 16 and above that number then it’s the new sensor (unless it is a very clever seller and the owner knows how to hack the M9 and set a fake number).

This all applies for M9, and M9-P but not M monochrome as far as I know.

Sensor Information: Displays details about the sensor, including the sensor ID and type.

Shutter Count: This shows the total number of shutter actuations, which can be useful for assessing the camera’s usage and wear.

The next two options should never be operated by the user of the camera

Two functions also show up in the hidden part of the menu, when operating this to check  are not intended to be operated by users. It is a technical setting that is only for Leica technicians to handle properly, according to information from Leica support. Therefore, do not click the colour shading or black level, as it might disrupt your pictures.It demands expertise and equipment to control and manage these.

Black Shading: This function helps to calibrate the sensor to achieve true black in images, similar to the black shading feature found in RED cine cameras.

Colour Shading: Adjusts the sensor to correct colour shifts and ensure accurate colour reproduction, but only to be operated by Leica technicians because it demands knowledge and expertise to measure and control the outcome.

These functions are particularly useful for advanced users who want to maintain optimal sensor performance and monitor the camera’s usage.