# Calculate boost from MAP Sensor via OBD-II

I'm working on a little project where I want to calculate the boost pressure (in bar) which my turbo currently produces. I use a wifi OBD reader that I plug into my car. I saw mobile apps calculating pretty accurate values based on my internal sensors.

Now my question: Which values do I need for calculating the actual boost? I found this forum where one guy explains a Formula. He uses the MAP sensor and a barometric pressure sensor. However I don't know which PIDs they are represented with. Until now I thought the "MAP" sensor is the "intake manifold absolute pressure", but on Wikipedia this values goes only from 0-255. Looks like a pretty unprecise indication.

Can anybody help me identifying the proper PIDs so I can calculate my current pressure?

• Not sure what the "Autotap" that he mentions is, but his formula - well what was explained between them is simple : reading - atmos P = boost P, where boostP is gauge pressure and the reading is absolute pressure. Jun 10 '17 at 17:25
• Yeah I understand that, but I'm not quiet sure which PIDs I have to read to get the needed values. it's actually the point where I'm getting confused. Jun 10 '17 at 17:39