If you’re even a little bit interested in working on cars — or, frankly, even just driving them — it’s worth your while to become familiar with the MAP sensor. It’s safe to say most of the automobile-owning public wouldn’t know this component on sight and couldn’t explain what it does if you asked. The truth is, we don’t think much about it until something goes wrong. When something goes wrong with the MAP sensor in your car or truck engine, it’ll let you know. Here are what it is and some of the telltale signs that it’s not working correctly.
What Is A MAP Sensor And How Does It Work?
The “MAP” in the MAP sensor is short for “manifold absolute pressure.” You may hear it used in conjunction with or instead of the term “MAF sensor.” Both sensors measure the air in the engine, but MAPs use air density as a baseline while MAFs use the airflow rate. Forced induction engines are generally equipped with both types of sensors.
When a MAP sensor begins operating improperly, it can and usually does impact the vehicle’s performance. If your car isn’t working the way you expect, it could signify a problem with this sensor.
So what does a MAP sensor do, and how does it do it?
Manifold absolute pressure sensors appear primarily in vehicles with fuel-injected engines, although there are rare exceptions. MAP sensors take continuous readings of how much air is entering the engine. Then, they calculate the air density there, as well as what’s called the “air mass flow rate.”
The MAP sensor then sends this data to the vehicle’s electronic control unit (ECU). It can then make on-the-fly adjustments to the engine’s ignition timing and the amount of fuel entering the cylinders and combustion chamber. This adjustment is necessary because any number of factors influence how hard an engine works. As the throttle opens and closes, and as the vehicle navigates hills, straightaways, and changes in altitude, the car must spend more or less fuel or air to provide the desired amount of power. It must maintain the right amount of vacuum relative to the outside barometric pressure. When the data indicates a change is required, the MAP sensor calls for a “richer” or “leaner” gasoline and air ratio.
MAP Sensor Symptoms
MAP sensors are vital for fuel metering and optimizing combustion within the engine. The lingering question is: How do you know when you have a faulty MAP sensor? Here are some of the symptoms you might experience:
- Disappointing Fuel Economy
If your vehicle isn’t getting the fuel economy it’s supposed to, and there’s a good chance it’s due to a malfunctioning MAP sensor. Because the sensor determines how much fuel is burned at any given time, a higher-than-accurate reading might cause you to get far below your expected MPGs.
- Loss Of Engine Power
A MAP sensor might also deliver a lower reading than the actual conditions warrant. In these cases, it causes the engine to receive less fuel than it needs. As a result, the motor will deliver insufficient or inconsistent amounts of power and a potentially dangerously unpredictable driving experience.
- Rough Idling
No vehicle should feel like a motel’s coin-slot vibrating bed while the engine is idling. If you’re experiencing a rough idle, it’s because the fuel injection system isn’t giving the motor the full measure of gas it requires.
- Cylinder Misfires
Your vehicle’s rough idle may or may not be joined by intermittent misfires from the cylinders. These will happen at random, or they may not happen at all.
- Failed Emissions Test
Your vehicle will not pass its next emissions test if its MAP sensor isn’t working correctly. If the MAP sensor is causing the engine to burn too much fuel, it will release more carbon monoxide (CO) and hydrocarbons (HC). On the flipside, starving the fuel engine is associated with higher nitrogen oxide (NOx) emissions.
- Difficulty Starting
Your car shouldn’t be difficult to start — and you shouldn’t have to depress the accelerator pedal to get it to fire up, either. A MAP sensor that’s signaling for too much or too little fuel in the ratio will play havoc with your car’s get-up-and-go.
- Hesitation And Poor Acceleration
It’s not just cold-starting the engine that becomes difficult with a bad MAP sensor. It also extends to your vehicle’s ability to accelerate. Next time you start pouring on the gas to pass somebody on a country lane and your car hesitates or fails to give you the power you need. It could be due to MAP sensor problems.
- Damage To The Engine
In the worst cases, trouble with the MAP sensor, and associated issues like vacuum leaks and lean fuel-air ratios, might damage the pistons and bearings. The catalytic converter could be ruined, and the engine will stop operating entirely.
Troubleshooting: What Causes A Faulty MAP Sensor?
If you’re experiencing any of these MAP sensor symptoms, you’ll want to be able to perform at least a basic troubleshooting and diagnostic session.
Where do you start your search? What can cause a MAP sensor to perform inaccurately or fail? Here are two systems:
- Electrical system: Ensure the MAP sensor’s electrical connections and the associated wiring are all firmly attached. None of the pins should be bent. Also, check the wiring connections between the MAP sensor and the engine control module or electronic control unit. Sometimes, the harsh conditions within the engine, coupled with vibrations and extreme temperatures over time, are enough to compromise the sensor’s internal circuitry.
- Hose and hose connections: If your MAP sensor is attached to the engine’s intake manifold via a hose, this is also a potential point of failure. Be sure there aren’t any cracks, kinks, signs of swelling, or loose connections. Look for carbon deposits or debris — they could be blocking the hose and causing the MAP sensor to deliver faulty readings.
If you, your mechanic, or your fleet manager can’t find anything wrong with these two systems, the problem is likely the sensor itself. This is one reason why it’s always useful to initiate a direct physical diagnostic connection during troubleshooting. OBD II codes P0106 through P0109 are related to manifold absolute pressure and barometric sensor functionality. You can also use a voltage meter along with a vacuum pump to perform your pressure and voltage testing and determine whether your MAP sensor itself needs replacing.
MAP Sensors And Automotive Self-Help
Those in the automotive and mechanic communities know the MAP sensor only too well. Hopefully, this crash course has been useful for casual automotive enthusiasts and drivers who just want to know their car a bit better.
Read More: OBD2 Codes: Full List Meaning & Fix Guide