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
A faulty MAP sensor will affect the ability of the ECM to adjust air/fuel ratio and ignition timing due to inaccurate calculation the engine load. This can result in an excessively rich or lean air-fuel mixture. Symptoms of a faulty MAP sensor can include:
- Malfunction Indicator Light (MIL) / Check Engine illumination
- Lean or rich air-fuel mixture
- Failed emissions test
- Poor fuel economy
#1. Malfunction Indicator Light (MIL) Illumination.
While driving, the engine control unit continually analyzes all of the sensors in your automobile engine. If a reading of one of these sensors is outside of the specified range, the check engine light will illuminate.
As a result, if your MAP sensor gives incorrect data to the engine management unit, the check engine light will illuminate on your dashboard.
If your check engine light has come on, below is a list of codes related with the MAP sensor to search for:
- P0068: Throttle Position Correlation
- P0069: Correlation of Manifold Absolute Pressure and Barometric Pressure
- P0105: MAP Circuit Failure
- P0106: MAP/Barometric Pressure Circuit Range/Performance Issue
- P0107: Low Input Manifold Absolute Pressure/Barometric Pressure Circuit
- P0108: High Input MAP Pressure Circuit
- P0109: Intermittent MAP / Baro Pressure Circuit
- P1106: MAP/BARO Pressure Circuit Range/Performance Issue
- P1107: Low Voltage Barometric Pressure Sensor Circuit
If your Check Engine light has come on, a list of codes related to the MAP sensor can be detected.
Please keep in mind that these codes might be set by defective sensors or other components. Even if your engine exhibits the symptoms described above and displays one or more of the OBD-II codes listed, it is suggested that you test the MAP sensor to determine if it is defective.
#2. Lean or Rich Air-Fuel Mixture.
A lean air-fuel ratio (too little fuel in the mixture) can cause surging, stalling, lack of power, hesitation on acceleration, backfiring through the intake, and overheating.
A rich air-fuel ratio (too much fuel in the mixture) can cause rough idling, poor fuel economy, sluggish acceleration. A rich air-fuel mixture can often be detected by a strong odor of gasoline when the engine is idle.
#3. Failed Emissions Test.
If the ECM cannot accurately control the air-fuel ratio, your vehicle may produce increased emissions and fail an emissions test.
Excessive fuel can lead to higher Hydrocarbon (HC) and Carbon Monoxide (CO) emissions, while insufficient fuel can result in higher Nitrogen Oxide (NOx) emissions. High emissions levels can damage the catalytic converter, leading to a failed emissions test for your vehicle.
#4. Poor Fuel Economy.
When A faulty MAP sensor sends incorrect values value to the ECM, the ECM will determine the engine is at high load. This causes the ECM to inject more fuel into the cylinders and advance spark timing, resulting in excessive fuel consumption, poor fuel economy, and detonation.
If you notice that your vehicle consumes more fuel than normal when driving a known distance, it may indicate a faulty MAP sensor.
Overall, there can be multiple reasons behind a faulty MAP sensor. As such, having an OBD2 scanner can be handy as it can help pinpoint the cause behind your broken MAP sensor.
#5. Lack of Power.
If the ECM is reading high vacuum, it assumes the engine load is low, so it cuts fuel injection and retards spark timing.
On the one hand, fuel consumption will go down, which seems like a good thing. However, if too little fuel is consumed, the engine may lack power for acceleration and passing.
Can I Drive a Car with a Bad MAP Sensor?
In most cases, you can technically continue to drive with a bad MAP sensor. But that doesn’t mean you should. It’s not a good idea to keep driving your vehicle without replacing its bad MAP sensor first.
Your car’s computer or powertrain control module (PCM) relies on the sensor’s readings to determine the right amount of fuel to inject into the engine cylinders.
In most cases, you can technically continue to drive with a bad MAP sensor. But that doesn’t mean you should.
If the computer adds too much fuel, the engine will run rich. Conversely, if it doesn’t add enough fuel, it will run lean. Since your vehicle’s engine is designed to operate within a certain range, running rich or lean can cause a variety of issues.
A faulty MAP sensor can lead to a wide range of engine performance problems and may even cause your vehicle to stall. What’s more, a faulty MAP sensor can potentially damage other parts of the vehicle.
Once you confirm that your vehicle’s MAP sensor isn’t working as it should, take your vehicle to a trusted auto repair shop. If you have plenty of experience with DIY auto repair, you can order an affordable yet high-quality replacement MAP sensor and install it yourself to save on labor costs.
If you are forced to drive before you can replace its faulty MAP sensor, avoid driving for long periods or over long distances. The longer the engine runs rich or lean, the greater the risk of damaging the vehicle.
How To Replace A Faulty MAP Sensor?
The average cost for a MAP Sensor Replacement is between $154 and $184. Labor costs are estimated between $39 and $50 while parts are priced between $114 and $135.
Replacing a bad MAP sensor varies by vehicle, so please consult the manufacturer’s service manual for instructions for any specific instructions. Once the faulty sensor has been removed, it’s a straightforward installation for the new part.
- Locate the MAP sensor on the intake manifold, either next to or on the throttle body itself, or on the intake manifold.
- Remove any screws or bolts holding the sensor in place.
- Disconnect the electrical connector. Note: Do not force removal as the connector may contain a locking tab that may need to be removed prior to unlatching the connector from the sensor.
- If applicable, detach the vacuum hose from the sensor. Note: It is recommended to replace the vacuum hose with a new hose when replacing the sensor.
- Compare the new and old sensors.
- If applicable, reconnect the vacuum hose.
- Reconnect the sensor electrical connector.
- Reinstall any screws or bolts that hold the sensor in place.
- Double-check all connections to make sure everything is secured.
Note: Depending on the vehicle and if a trouble code was set, a diagnostic tool may be required to reset the check engine light.