9 Symptoms of a Bad MAP Sensor
We’ll explain how this inexpensive type of sensor works and explain the most common symptoms of failure, so you’ll be equipped with the knowledge to diagnose the problem and possibly fix it yourself. At the very least, you’ll avoid getting ripped off at a workshop.
How the MAP Sensor Works
An internal combustion engine is really just a fancy air pump. The readings taken by the MAP sensor are an approximation of the air density in the engine at a given time, and are used in the ECU’s Volumetric Efficiency (VE) tables.
A volumetric efficiency table is a 3D graph that represents how much air the engine can move at a given air density and engine speed.
Note that the amount of air in the engine depends on how hard you press the accelerator pedal (throttle valve). The accelerator pedal controls the throttle valve, which cuts off the air supply to the intake manifold. For every 14.5 psi of boost pressure, the MAP sensor must be able to measure 1 bar better.
Many modern turbochargers have a boost pressure of around 20 psi, which would require a 3 bar MAP sensor.
As the name suggests, the MAP sensor measures absolute pressure, so it never measures negative values like a vacuum or boost pressure gauge. A MAP value of 0 bar represents a perfect vacuum.
Symptoms of a Failed MAP Sensor When a MAP sensor does not work, it usually results in an inaccurate mixture. Depending on how the sensor failed, the mixture may be too rich (too much fuel) or lean (too little fuel).
The ECU may try to rely on other sensors to make up for erroneous readings or a complete lack of data. One such sensor is the O2 sensor.
Below are the 7 most common signs of a faulty MAP sensor.
1) Rich Mixture
When the air-fuel mixture is too rich, the following can happen:
– Spark plugs may foul.
– Carbon deposits may form more quickly. – The catalytic converter may become clogged.
– The exhaust may have a stronger gasoline smell.
– Fuel consumption will be affected.
2) Lean Mixture
If the mixture is too lean, the results may be even worse.
– Lean combustion results in higher temperatures, which can damage or shorten the life of engine components over time due to excessive heat.
– A lean air-fuel mixture also produces harmful emissions such as carbon monoxide (CO) and nitrogen oxides (NOx).
– You are more likely to experience pre-detonation (also known as engine knock). Knocking under load can lead to catastrophic failure that can damage the entire engine.
3) Poor Fuel Economy
A common symptom of a faulty MAP sensor is worse than normal fuel economy. If there is a problem with the sensor, it can send false signals to the vehicle’s engine management system. This can result in the engine consuming more fuel than normal and resulting in poor fuel economy.
4) Check Engine Light
If your vehicle has an OBD2 port (1996 or later), the check engine light may come on if a problem with the MAP sensor is detected. Common issues include DTC P0106, DTC P0107, DTC P0133 and/or DTC P0299 on turbocharged/supercharged vehicles.
5) Misfire
If your vehicle no longer has an ideal air-fuel mixture, your engine may have trouble maintaining complete combustion. Incomplete combustion can cause a misfire. In some cases, it may even turn on its own check engine light.
6) Failing Emissions Tests
If you live in an area where you must pass an emissions test to register your vehicle, a faulty MAP sensor can cause your vehicle to break down due to an increased presence of harmful gases or even turn on your check engine light.
7) Rough Idling
An incorrect air-fuel ratio can cause excessive engine vibrations at idle or randomly increase your idle speed.
8) Stuttering, Hesitating, or Stalling
When you press the gas pedal in a hurry to pass or get out of traffic, your engine may squeak, hesitate, sputter, or stall. These are all symptoms that indicate something is wrong with the air-fuel mixture and that the sudden introduction of too much air is making it difficult for your engine to keep up with the suddenly demanded load.
9) Hard Starting
Since the MAP sensor is responsible for monitoring intake manifold pressure, it plays an important role in the air-fuel mixture that enters the engine.
If the sensor is delivering inaccurate information, your engine may struggle to maintain the proper air-fuel ratio, causing hard starting or even stalling. This can be particularly noticeable when the engine is cold or during rapid changes in temperature.