will always read 100 kPa more than a boost sensor measuring the same conditions. A MAP sensor will never display a negative reading because it is measuring absolute pressure, where zero is the total absence of pressure. Vacuum is measured as a negative pressure relative to normal atmospheric pressure. Vacuum-Boost sensors can display negative readings, indicating vacuum or suction (a condition of lower pressure than the surrounding atmosphere). In forced induction engines (supercharged or turbocharged), a negative boost reading indicates that the engine is drawing air faster than it is being supplied, creating suction. The suction is caused by throttling in spark ignition engines and is not present in diesel engines. This is often called vacuum pressure when referring to internal combustion engines. In short, in a standard atmosphere most boost sensors will read one atmosphere less than a MAP sensor reads. At sea level one can convert boost to MAP by adding approximately 100 kPa. One can convert from MAP to boost by subtracting 100 kPa. External links MaP sensor Engine fuel system technology Engine sensors