9 Symptoms of a Bad MAP Sensor
Having problems with your engine? A faulty MAP sensor could be the culprit, and knowing this could save you money.
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 you need to diagnose the problem and possibly solve it yourself. At the very least, you’ll avoid getting ripped off at the workshop.
How the MAP Sensor Works
An internal combustion engine is really just a fancy air pump. The measurements 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) table.
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. The ECU then uses this table in its fuel equation to calculate how much fuel should be injected at any given time.
Note that the amount of air in the engine depends on how hard you press the accelerator (throttle) pedal. The accelerator pedal controls the throttle valve, which cuts off the air supply to the intake manifold. When a naturally aspirated vehicle (one without a turbocharger or supercharger) is at wide open throttle, the absolute pressure in the intake manifold is nearly equal to the ambient air pressure. Since 1 bar is approximately equal to sea level air pressure, these vehicles require a MAP sensor that accurately measures 1 bar or better.
Forced induction vehicles require a MAP sensor that can accurately measure up to 2 bar of boost pressure, and possibly more, depending on the amount of boost pressure the vehicle produces. For every 14.5 psi of boost pressure, the MAP sensor must be able to accurately measure 1 bar more.
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.
Vehicles without a MAF sensor usually have an IAT sensor to compensate for errors in air density estimation caused by ambient air temperature.
Symptoms of a Bad 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 that indicate a faulty MAP sensor: #1 – Rich Mixture
If the air/fuel mixture is too rich, the following can happen:
1. Spark plugs can foul.
2. Carbon deposits can form more quickly.
3. The catalytic converter may become clogged.
4. The exhaust may have a stronger gasoline smell.
5. Fuel consumption will be affected. #2 – Lean Mixture
If the air/fuel mixture is too lean, the consequences can be even worse.
1. Lean combustion results in higher temperatures, which can damage or shorten the life of engine parts over time due to excessive heat.
2. A lean air/fuel mixture also produces harmful emissions such as carbon monoxide (CO) and nitrogen oxides (NOx).
3. 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 – High Fuel Consumption
A common symptom of a bad MAP sensor is worse than normal fuel economy. If there is an issue with the sensor, it can send false signals to your vehicle’s engine management system. This can result in your 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 newer), 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.
Have the code read at a repair shop or auto parts store (or at home if you have a diagnostic tool) to determine if the cause of the check engine light is a faulty MAP sensor.
#5 – Misfire
If your vehicle no longer has an ideal air-fuel mixture, the engine may have difficulty maintaining complete combustion. Incomplete combustion can cause a misfire. In some cases, it may even turn on its own check engine light.
#6 – Failed Emissions Test
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 an illuminated check engine light.
#7 – Rough Idling
An incorrect air-fuel ratio can cause your engine to vibrate excessively at idle or randomly increase your idle speed.
#8 – Stumbling, Hesitation, or Stalling
When you stab the gas pedal to pass quickly or pull out in front of traffic, you may notice the engine bog, hesitate, stumble, or stall. These are all symptoms that something’s not quite right with the air fuel mixture, and the sudden introduction of a whole lot of air has made it more difficult for the engine to keep up with the sudden requested 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.
