The Manifold Absolute Pressure sensor measures the intake manifold pressure (IMP) downstream of the throttle valve in order to indirectly compute — by means of the ratio of pressure to engine speed — the amount of air drawn in. It measures the pressure in the intake manifold (IM) and transmits this information as an electrical signal to the engine control unit.
As a rule, it is mounted directly on the IM. The pressure generally acts on a piezoelectric element, which then produces a corresponding output signal via an electronic circuit. This can be a PWM signal or an electrical voltage.
Symptoms of malfunctions
It can become clogged, damaged, or contaminated. Sometimes excessive engine heat can damage it or the vacuum lines. If it is not working properly, the ECU cannot accurately calculate the air-fuel mixture, which means that this mixture is too rich or too insufficient. Here you have some symptoms of a faulty MAP sensor:
Increased fuel consumption
An IAP sensor showing increased pressure at the intake manifold indicates a high engine load compared to the PCM (drive system control module). This results in the injection of a larger quantity of fuel into the engine than needed. It also increases fuel consumption, as well as the amount of gaseous emissions into the environment. Hydrocarbons and carbon monoxide are some of the elements that end up in smog.
Lack of performance or the engine has low propulsion power
A sensor that indicates low IMP actually means that the power load for the PCM is low. PCM responds to a decrease in the amount of fuel that is injected into the engine. Although you may find that you are saving fuel, you will also find that the car does not run as well as before. Reducing the fuel supply to the engine increases the temperature in the combustion chamber. This increases the level of nitrogen oxides produced. Nitrogen monoxide is also a component of smog and has a negative effect on our environment.
Engine failure while driving or by starting
If the MAP is faulty, the car may not run when you expect it to or run less, or in either case the performance will be affected. If, for example, while trying to pass another vehicle, the car does not accelerate smoothly. A lean or very rich air-fuel mixture makes it difficult to start the vehicle. If it only starts when you step on the accelerator, there is a good chance that the sensor is faulty.
What happens if I unplug it
It is not advisable to drive without it. Your vehicle will not run as efficiently if it doesn’t have the readings from the sensor. The engine and catalytic converter could get damaged and wear out more quickly. If you suspect that there is a problem with it, it’s a good idea to test it right away.
How to test a MAP sensor
Most are connected to the intake manifold via a hose. Make sure that it is connected and in good condition. Also check if the hose is clogged or cracked. This may lead to an abnormal readout. If it is properly connected both to the electrical system and to the intake manifold, use a voltmeter to measure the output voltage. After reading the output voltage, compare the result with the manufacturer’s specifications. Check the intake manifold sensor connector and the system wiring. The connector may be damaged by corrosion or some wires may be short-circuited. If the sensor is corroded, the problem can be fixed by cleaning the MAP sensor
Testing with a multimeter
If you choose to test for malfunction with the multimeter, make sure to use one with a minimum of 10 meg. This ensures that you won’t damage any other sensitive electrical devices in your car.
How to clean a MAP sensor
First, wearing a pair of rubber gloves and safety goggles, disconnect it. Using a paper towel or soft cloth, and an electric parts cleaner, remove the grime on the sensor. Spray the cleaner inside – a couple of spritzes are enough. Shake off any surplus cleaner and allow it to dry completely. Take a look at the vacuum hose or the intake manifold connection. If you see more dirt or grime, clean the hose with the same product and a brush. After everything has dried, it should be clean and can be reinstalled.