What is a Manifold Absolute Pressure (MAP) Sensor? What is the MAP sensor? What is the MAP sensor’s function? What are the symptoms for MAP sensor malfunctions? What are the types of MAP sensor fault codes?
The Manifold Absolute Pressure Sensor, MAP / Manifold Absolute Pressure, is one of the key sensors used to detect engine load. The sensor produces a signal proportional the pressure in the intake manifold. This information is used to adjust the timing of ignition and fuel consumption by the engine computer (PCM).
As the throttle opens, the intake pressure falls when the engine is in operation. To keep the fuel/air ratio balanced, the engine needs to take in more air. The PCM usually maintains a slightly richer fuel mixture by reading signals from MAP sensors. The engine will produce more power. It will also delay the ignition timing slightly to prevent performance degradation and recoil that could damage the engine.
It will require less engine power when the vehicle is under light loads and it returns to normal cruise speed. The intake pressure will rise if the throttle isn’t fully open or closed. The MAP sensor will detect this and report it to the PCM. To reduce fuel consumption, the PCM reacts by decreasing fuel delivery and increasing ignition timing.
How does the MAP sensor work?
The MAP sensors measure pressure in the intake manifold. It is also known as the intake manifold pressure sensor. The pressure in the intake manifold will be the same as the barometric pressure outside the engine when it isn’t running. Because of the restriction created from the throttle plates, the pistons and throttle plates restrict the flow of air into the intake manifold. The intake manifold pressure drops to nearly zero when the engine is at maximum throttle and the throttle is fully open. The external barometric pressure equals the pressure in the intake manifold.
Depending on the location and climate, barometric pressure will vary from 28 to 31 inches (average 1 bar) depending on where it is. The air pressure drops as you rise above sea level.
Depending on the operating conditions, the pressure in your intake manifold could range from zero to 22 inches Hg. The pressure when the engine is running is constant at 16 to 20 inches Hg, depending on the vehicle. When the vehicle is slowed down and the throttle is shut, the pressure rises to its highest level. The intake manifold is able to produce high pressure when the throttle is closed and the pistons are working. Usually, four to five inches Hg more than at idle. The throttle will open suddenly and the vehicle will accelerate. When the throttle is closed, pressure begins to rise again.
The engine control module, or PCM, learns the atmospheric pressure (or barometric) by turning on the ignition. You can use the MAP sensor double-duty as a BARO sensors. This information is used by the PCM to adjust the air/fuel mixture and compensate for changes in pressure. This is done by a different “BARO” sensor in some vehicles. Some vehicles use a combination sensor (called a BMAP sensor) that takes both measurements.
This situation is slightly more complex for supercharged and turbocharged engines. Turbo boost will create extra pressure in the intake manifold. This is not a problem, as the MAP sensor measures absolute pressure in the intake manifold.
The air flow is measured by the electronic fuel injection system Speed-Density. To estimate the amount of air entering the engine, the PCM examines the MAP sensor signal, engine speed, throttle position and coolant temperature. The position of the EGR val and oxygen sensor rich/lean signals can be taken into consideration by the PCM to maintain balance and make adjustments to the fuel mixture.
Analog MAP Sensors
Analog MAP Sensor consists two chambers that are separated by a flexible dial. The “reference air” chamber is closed or open to outside air. The vacuum chamber is connected to the engine via a rubber tube or directly to the intake manifold. The MAP sensor can be attached to the intake manifold via a hose.
A pressure sensitive electronic circuit within the MAP sensor monitors the movement of the diaphragm and generates a voltage signal. This signal varies in proportion to pressure. The signal is usually between 1 and 5 volts.
Three-wire connectors are used for analog MAP sensors.
- – The Earthing Connection
- – A reference signal of 5 volts from the ECU
- – turn signal
The output voltage generally increases as the throttle is opened and pressure drops. The voltage at idle is approximately 1 to 2 volts, but it increases to 4.5 to 5 volts when you open the throttle fully. For every 5 inHg pressure change, the voltage ranges between 0.7 and 1.0 volts.
Digital Map Sensors
Digital MAP sensors (barometric and manifold absolute pressures) can also measure engine load but produce a digital frequency instead of an analog voltage. This sensor type has an additional circuit which generates a 5 Volt “square wave” voltage signal (on-off). The voltage frequency will increase as the pressure drops.
The engine is either idling, or slowing down, so the pressure is high. The MAP sensor output drops below 100 Hz (Hertz-cycles per second). Full throttle may cause the output to rise to 150Hz or more, since the pressure in the intake tube will be near zero. The MAP sensor should read 159Hz when the pressure has been completely reset.
Malfunction of the MAP Sensor Symptoms
The fuel mixture and ignition timing can be affected if the MAP sensor does not correctly read pressure readings. You can see MAP sensor problems in wiring harness disconnections, socket looseness or intake manifold cracks.
MAP sensor failure can lead to the following signs:
- – Sudden acceleration/deceleration of vehicle
- RPM fluctuation at idle
- – Use a rich fuel mixture to contaminate spark plugs
- – Blazing due to dry fuel and over-ignition
- – Excessive fuel use and power loss as a result of deterioration in ignition timing and air/fuel combination
The MAP sensor will read higher than normal if there are air leaks. ECU will compensate by enhancing the fuel mixture and increasing the ignition timing in order to improve fuel economy, reduce emissions and increase performance.
Failure of the MAP Sensor
First, ensure that the engine is idling while the manifold pressure remains within the specified range. Air leaks, delayed ignition timing and exhaust restriction (clogged converter) can all lead to extremely low pressure.
The MAP sensor can be misled by low pressure or high back pressure in the exhaust system. This could cause the sensor to read incorrectly as if the engine has been overloaded. This can lead to a rich fuel mix.
However, an obstruction in the air intake, such as a clogged or blocked air filter can cause higher pressure. This will indicate a low engine load and cause the MAP sensor to mislead, which can lead to the engine becoming lean.
Before the engine is started, the MAP sensor should measure the barometric pressure. This value should be compared with outside air pressure and can be read using a scanner. On the Meteorology site, you can find the atmospheric pressure value for your current location.
For leaks or kinks in the vacuum hose, check the sensor. Use a handheld vacuum to test the sensor for leaks. The pressure should not be exceeded by the sensor. Any leakage will require replacement.
If the MAP sensor is not working properly, the signal may be lost due to wiring issues or the sensor readings are incorrect, the fault code will usually be generated and the check engine light will illuminate.
MAP Sensor Fault Codes
For 1995 and newer OBD II-capable vehicles, trouble codes (DTCs P0105 to 0109 indicate a problem with the MAP sensor circuit.
P0105… MAP/BP Circuit Malfunction
P0106… MAP/BP Limit Sensor Limit / Performance Issue
P0107… MAP/BP Low Input Sensor
P0108… High Input MAP/BP Sensor
P0109… MAP/BP Circuit Intervals
Older OBD II cars
* General Motors: 34, 33, 31 Codes
* Ford: 22, 72 Codes
* Chrysler: Codes 13, 14 indicate MAP sensor failure.
You can read the output voltage of the sensor using the diagnostic tester. The specifications should be compared to the values. The MAP sensor signal should change when the throttle is open or closed. Any change in the MAP sensor signal should indicate a connection fault or sensor fault.
If the sensor is not responding or reading correctly, then check the ground and reference voltage. The reference voltage should not be less than 5 volts. Low reference voltages should be checked for damage, corrosion, or loose connections.
Replacing a defective MAP sensor
The appropriate type of sensor for your vehicle should be chosen if the MAP sensor becomes defective and must be replaced. Use the MAP sensor that is compatible with the year and model of your vehicle. Engine operation can be affected by differences in calibrations.
The vacuum hose that connects the engine to the MAP sensor will need to be replaced if the vehicle is older than five years.
