In fuel-injected automotive engines, a manifold absolute pressure (MAP) sensor is used to continuously monitor the amount of air flowing into the engine, so the computer can calculate air density, adjust the amount of fuel to spray into the combustion chamber and adjust the ignition timing. In some vehicles, a mass air flow (MAF) sensor is used. While the two are interchangeable, a MAF sensor measures flow rather than density.
A failed MAP sensor can cause your vehicle to have a few performance problems. If the sensor is in error, reading too high, it can cause the fuel management system to use more fuel than is needed and decrease fuel economy. Conversely, if the MAP sensor reads too low, the onboard computer will trim back the amount of fuel it thinks is needed and starve the engine, causing it to run erratically and decrease power. In either case, if the sensor isn’t reading properly, it will cause your vehicle to fail emissions testing.
Reasons for a MAP sensor failure can be caused by a few factors. The sensor itself relies on both electronic and mechanical components to function. A vacuum chamber inside the sensor is what allows the the sensor to read changes in the manifold pressure. Over time a leak can develop in the vacuum chamber, making the sensor unable to read correctly. Due to the location of the sensor in the harsh engine compartment environment, years of extreme temperature fluctuations and vibration can also wreak havoc on the internal circuitry. Another failure point can be dirt or other contamination physically preventing the sensor from accessing the intake manifold air flow.