Whether it is a naturally-aspirated or a turbocharged internal combustion engine, it is a big vacuum pump that sucks air as its pistons move up and down. When this happens, the pressure inside the intake manifold drastically changes which affects engine operation. To keep this under control, the engine control unit relies on the manifold absolute pressure (MAP) sensor that monitors pressure changes and sends these data to the computer. Its failure may cause several engine troubles, including the following ones:
Poor acceleration and overall performance
Your engine control unit uses signals received from the MAP sensor to calculate how much fuel and ignition advance needed for smooth and efficient engine operation. Incorrect data received from the sensor will cause the engine control unit to miscalculate the amount of fuel and ignition timing advance, resulting in poor performance. Turbocharged engines are especially vulnerable to these changes due to the extremely high pressure they deal with.
Engine shaking and misfiring
A faulty MAP sensor will report false pressure readings. If they are high, the computer will add more fuel to the air/fuel mixture, which may foul spark plugs and cause misfiring. If so, the engine will shake, and you will feel this motion driving the vehicle.
Abnormal sounds from the engine
A faulty MAP sensor can make the engine run too lean or the spark plugs fire when this is not necessary. This will cause detonation, so you’ll hear pinging sounds when pushing down the gas pedal. You should not ignore this problem as it may destroy your engine.
Poor fuel economy
As it described above, a faulty MAP sensor may cause the engine to run too rich, which will affect your fuel consumption.
Your engine stalls or surges
A poor MAP sensor may influence the idle speed of the engine if it sends incorrect readings. The engine can surge or idle too slowly. If the latter is the case, the engine can stall when you turn on the air conditioning or another power consumer.
You can’t start the engine
The engine control unit relies on your MAP sensor to read the atmospheric pressure and to calculate the amount of fuel needed for an engine start. Incorrect MAP sensor readings will lead to either a too lean or too rich air/fuel mixture. Whichever happens, the engine won’t start easily.
The check engine light comes on
The engine control unit compares data received from different sensors. If the MAP sensor shows high vacuum, but the throttle sensor says that the throttle body is fully opened and the RMP is climbing, the control module will know that the MAP sensor sends wrong readings since the vacuum is greatest at low speeds. If this happens, the computer will alert you of the problem.
Limp-home mode is activated
If the engine control unit finds that the MAP sensor is faulty, it can activate a safety feature, known as limp-home mode. Common for modern vehicles, this safety feature will cause the engine to reduce its power and will leave you stuck with just a couple of gears, so you can slowly get to a repair shop without running the risk of damaging the engine.
What is a MAP sensor?
A manifold absolute pressure sensor can be found on the intake manifold or in the vacuum hose of just about any modern gasoline or diesel engine.
Unlike some other engine sensors, the MAP sensor starts working once you press the start button or turn your key. Before the engine starts, the sensor receives a voltage reference from the engine control unit, and uses it to measure the absolute pressure by means of a pressure-sensitive electrical circuit that reads the movement of an internal rubber diaphragm. After that, the MAP sensor sends this reading to the control module.
When the engine is running, the pressure inside the intake manifold varies depending on the location of the throttle. These pressure changes cause movements of the diaphragm, which are transformed into electrical signals sent to the ECU. The computer uses these data along with readings from other sensors to measure how much fuel and what ignition timing needed for smooth and efficient engine operation.
On some newer vehicles, a MAP sensor is also used to monitor exhaust gas recirculation, which is crucial for low emissions.
MAP sensor maintenance and repairs
Most MAP sensors are designed to last the life of a vehicle. However, as it contains a moving rubber diaphragm that is prone to wear and tear, it may fail to operate as expected.
A faulty MAP sensor should be diagnosed by a professional using a special scan tool. He or she will perform electrical testing to check its operation.
A bad MAP sensor is not repairable and should be replaced. The cost of a replacement unit and labor may vary depending on your vehicle and the placement of the sensor.
Every MAP sensor is model specific, which means you must use original replacement parts or identical to them high-quality aftermarket parts. You should not compromise on its quality as this sensor is crucial for your engine operation.
Can I replace a MAP sensor myself?
Unless you’re a professional mechanic, we recommend you to leave this job to a professional. While the sensor is usually easy to access and replace, its diagnosis is a complex procedure which requires a special knowledge and specific diagnostic tools. You’ll save some money if you let a mechanic do the trick.
A typical MAP sensor features an electrical connector with three wires, and two small screws that secure it onto the intake manifold. Whether it is mounted on the manifold or on the intake tube, it has a seal on its back. Remotely mounted MAP sensors feature a nipple that goes into a hose or tube. Regardless of its type, the sensor must be properly secured and sealed.
The screws that secure a MAP sensor are usually weak, which is why overtightening the screws is unacceptable.
Once the job is done, you should reset the engine control unit to clear out trouble codes and do a test drive to make sure everything is fine