The altimeter reading on my MMCS used to work but now always shows zero.

Is there a sensor I can easily check to see if it is blocked or dirty?

 

The altitude is obtain on the information that satellites GPS send through their signals, therefore, requires that antenna GPS "sees" 4 satellites at least to exhibit the altitude, estimating the amount of time it takes for their signals to reach the receiver. I suggest you verify the amount to you of satellite that you GPS antenna receive, and if the 3D indicator come ON. In addition, exhibit your MMCS the latitude/longitude coordinates?

 

Thanks for the information.

I checked the number of satellites and it varies between seven to ten, the 3D indicator was also on and the latitude/longitude co-ordinates were detailed.

When I switched back to the altimeter it has stated working again! I will keep checking and see if it continues to work.

Does the barometer also work from the satellite data?

 

Good news. The amount of satellite that tunes your antenna GPS "see" must give the altitude information, although in my Outlander, this data is very erratic (I live to 60 msnm and the MMCS gets to me to indicate up to 200 msnm).
About the barometric pressure, this is measured with a barometer but I not if the MMCS has or not this device, although in theory, it must have it, because the information that sends satellites GPS indicates its location and the current Time. . .