In modern engines, the engine control module (ECM) measures or calculates air flow via either a mass airflow (MAF) or manifold absolute pressure (MAP) sensor. Turbocharged engines may use both, but naturally aspirated engines typically use one or the other.
If the MAP sensor is failing or broken, the ECM—and thus, the engine—can’t function properly. By maintaining and repairing your MAP sensor, you’ll keep your engine running smoothly.
What Is a MAP Sensor?
The manifold absolute pressure sensor reads the amount of pressure or vacuum (also called “engine load”) in the intake manifold, where outside air is divvied up in proper amounts and distributed to each cylinder.
This pressure reading is shared with the engine control module to determine how much fuel needs to be fed to each cylinder, as well as to determine ignition timing. A fully functioning MAP sensor is necessary to maintain the right combination of acceleration, fuel economy, emissions and engine smoothness.
When the throttle is wide open and air is rushing into the intake manifold (causing a drop in pressure), the MAP sensor signals the engine computer to send more fuel. When the throttle closes, pressure rises and readings from the MAP sensor tell the computer to reduce the amount of fuel going into the engine.
A faulty MAP sensor will usually trigger a “check engine” warning light. Other signs of a bad MAP sensor include rough idling, sluggish acceleration or hesitation, poor fuel economy or black smoke coming out the exhaust.
Not only can the sensor fail, but vacuum hoses can develop leaks or electrical contacts can fail, triggering the warning light or causing other issues. Some vehicles use a mass air flow sensor instead of a MAP sensor to measure the amount of air going to the intake manifold.
How Does A MAP Sensor Work?
The MAP sensor is typically located on the intake manifold, either next to or on the throttle body itself. (On a forced-induction engine, the MAP sensor can be found on the intake tract before the turbo.)
Inside the MAP sensor is a sealed chamber that either has a vacuum or a controlled pressure that is calibrated for the engine. Dividing the sensor vacuum and the vacuum from the intake manifold is a flexible silicon wafer (a.k.a. ‘chip’) with a current running through it.
The MAP sensor performs ‘double duty’ as a barometric pressure sensor as soon as the key is turned on.
With the key turned on (prior to the engine starting) there is no vacuum in the engine applied to the MAP sensor therefore it’s signal to the ECM becomes a baro reading helpful in determining air density.
When you start the engine, pressure in the intake manifold decreases creating a vacuum that is applied to the MAP sensor. When you press on the gas accelerator pedal, the pressure in the intake manifold increases, resulting in less vacuum.
The differences in pressure will flex the chip upward into the sealed chamber, causing a resistance change to the voltage, which in turn tells the ECU to inject more fuel into the engine. When the accelerator pedal is released, the pressure in the intake manifold decreases, flexing the clip back to its idle state.
The ECU combines the manifold pressure readings from the MAP sensor with data coming from the IAT (intake air temperature), ECT (Engine Coolant Temperature) sensor, baro reading and engine speed (RPM) to calculate air density and accurately determine the engine’s air mass flow rate for optimal air-fuel ratio.
What Happens When the MAP Sensor Goes Bad?
Your vehicle’s PCM uses the readings from the MAP sensor to determine engine load. If the sensor sends the wrong information or stops working altogether, the computer may set the wrong air-fuel ratio.
This can lead to either the engine running rich or running lean, both of which are bad for your ride in different ways. A faulty MAP sensor may also affect ignition timing, exhaust gas recirculation (EGR) operation, and other operating parameters.
As a result, a faulty MAP sensor can lead to a variety of engine performance problems, such as misfiring, rough running, and stalling. A bad MAP sensor will also likely turn on the check engine light. If you continue to drive the vehicle with a failed MAP sensor, you risk damaging other parts of the vehicle, as well.
Symptoms of a Faulty MAP Sensor
The usual signs of a faulty MAP sensor are poor fuel consumption and a check engine light. Other symptoms you might notice include a misfiring or stalling engine, and rough idle or difficulty starting.
Any issue with the MAP of the manifold absolute pressure sensor will create an improper combustion cycle which causes damage to the engine and its performance.
Here is a more comprehensive list of symptoms of a bad or failing MAP sensor that you should watch for:
#1. Check Engine Light.
The engine control unit tracks all the sensors in the car engine while you’re driving the car. If any of these sensors are out of the specified range then the check engine light comes on.
So if your MAP sensor sends incorrect information to the engine control unit, the check engine light will come on as displayed on your dashboard.
#2. Lean Air-fuel Mixture.
The MAP sensor measures the air pressure in the intake manifold to determine the proper air-fuel mixture for your engine. A bad MAP sensor might cause your engine to receive a too lean air-fuel mixture.
The lean fuel mixture can cause many weird symptoms in your engine, which you will see down the list.
#3. Rich Air-fuel Mixture.
The opposite is also true. If the MAP sensor has a problem, it could send a faulty signal and cause the ECU to inject too much gasoline into the car engine.
A rich air-fuel mixture not only means that your car is using extra fuel, but it can also present performance-related issues.
#4. Stalling or Rough Idle.
If you have a bad MAP sensor that results in too rich or too lean of an air-fuel mixture, you will notice issues at the engine’s idle. The engine is very sensitive when running at idle. Therefore, when it is running, you’ll likely notice a faulty air-fuel mixture when the engine is sitting at idle.
There are many other faulty components that can also cause a faulty air-fuel mixture, so it should be diagnosed properly versus just replacing the MAP sensor.
#5. Misfires.
Misfires happen when combustion does not happen inside the engine cylinder, which can happen because of a wrong air-fuel mixture or bad spark, either may also be caused by a bad MAP sensor which may actually cause the air-fuel to get so bad that you would notice misfires.
You can hear misfires most of the time. If you hear the engine making little bumps or doesn’t sound like it normally sounds, then misfires are occurring.
#6. Increased Emission Level.
When the manifold absolute pressure sensor (MAP) suffers damage, it could send a false high or low engine load signal to the powertrain control module (PCM).
Like any engine, to obtain a good emission level in your car, the air-fuel mixture must be correct. In fact, just a little malfunction with the MAP could alter the air-fuel mixture enough to have an impact on emission levels.
#7. Bad Engine Performance.
A bad fuel mixture will cause poor engine performance. A lean mixture normally causes poorer performance, but an overly rich mixture can absolutely cause the same.
Poor engine performance can also be caused by misfires caused by a bad MAP sensor as we discussed earlier in this article.
#8. Backfires.
Backfires occur when fuel passing through your engine gets burned incorrectly. When the fuel isn’t ignited in the combustion chamber, it makes its way to the exhaust pipe.
As you can imagine, the exhaust pipe gets extremely hot, and just as the combustion chamber ignites the air-fuel mixture, this air-fuel mixture can ignite in the exhaust pipe.
This causes loud bangs coming from the exhaust system, and it can even cause your mufflers, etc., to explode. If you are really unlucky, it can even cause your car to catch on fire.
#9. Hard Starting Condition.
A faulty MAP sensor also causes problems with starting the car. The car’s trip computer uses the MAP sensor to measure air pressure prior to engine start.
The engine is very particular about appropriate air-fuel mixture on the initial moment of starting the engine, thus a either too little or too much fuel may never be delivered or the engine will never start or run properly.
#10. Changed fuel consumption.
If you have read the previous article, I think you now understand this best! Obviously, an out-of-spec air-fuel mixture resulting from a bad MAP sensor would also lead to a different rate of fuel consumption.
If you start to notice your vehicle needs less or more fu, then the most likely issue is bad MAP sensor.
MAP sensor location
In most car models, the MAP sensor is located on the intake manifold. It can also be installed on the body of the car on a vacuum hose from the intake manifold.
The MAP sensor’s location will depend on your car’s design, and you should consult the service manual to find the exact position of the MAP sensor in your car.
MAP Sensor Replacement Cost
Replacing a MAP sensor averages between $60 to $170, based on the vehicle model and labor rate. Labor costs range between $30 to $70, while the sensor itself costs $30 to $100.
Replacing a MAP sensor usually isn’t that difficult, and something you can do yourself at home for most vehicles. If you have a bit of vehicle knowledge, it is a good way to save money.
Diagnosing a Bad MAP sensor
Diagnosing a bad or malfunctioning MAP sensor can be done by initially observing the current symptoms in your vehicle and subsequently performing a physical test for diagnostic purposes.
This is the easiest way to test the MAP sensor is by connecting a Diagnostic scanner to observe the value of the MAP sensor.
You should be reading close to 1 bar or 14.5 psi when the ignition is on but the engine is off. Take a look at this video with the correct MAP sensor testing procedure: MAP sensor testing.
Following is a short step-by-step guide that you can follow to check, test and diagnose if the MAP sensor in your vehicle has gone bad.
- Find the MAP sensor of your engine by inspecting it yourself or finding it in the vehicle service manual.
- Make sure the vacuum hose plugged into the MAP sensor is attached properly and in good condition.
- Check to see if the connections and wiring are in good condition as well.
- Clean the sensor with an electronic cleaner, and check again with your diagnostic scanner.
- Check the MAP sensor directly after these instructions.
- Measure the wirings between the engine control unit and the MAP sensor.
- Replace the MAP sensor if faulty or repair wirings.
FAQs.
Q: Can I drive my car with a bad map sensor?
A faulty MAP sensor can lead to an air-fuel mixture that is too rich or too lean. Consequently, since you might experience problems with engine performance, driving with a faulty MAP sensor is frowned-upon.
You may drive at a slow pace to the nearest mechanic, as long as the car still runs.
Q: How can you tell a map sensor is bad?
Most of the time with a bad MAP sensor you will simply see a check engine light on your dash.
You could always use a diagnostic tool to look at the values that your MAP sensor is sending to the ECU.
Q: How much does it cost to fix a map sensor?
The biggest cost consumers will incur is labor because the MAP sensor is often relatively cheap, not to mention the average DIY fix for a guy is at home. A new MAP sensor is roughly 30-70$ and the labor work is 30-100$.
Q: Can a map sensor be cleaned?
Yes, over time there will often be soot and debris on the MAP sensors measure head (the end piece that measurement is taken). Generally speaking, an electrical cleaner can clean a MAP sensor. Caution with the measurement head cleaning is recommended as it can be damaged in the cleaning process. In some cases, you do have to replace the MAP sensor.