The manifold pressure sensor, which is also known as the manifold absolute pressure (MAP) sensor is an integral part of the vehicle’s engine system.
It is found in the fuel injected vehicles as the main job of the MAP sensor is to provide the Powertrain Control Module (PCM) with information about the pressure inside the manifold intake.
Like any sensor in your vehicle, the MAP sensor can get damaged over the time and may result in transmitting incorrect data to the engine control unit. This incorrect information can cause damage to the performance, drop in fuel economy and several other consequences. In this article, we will discuss some of the key symptoms you will experience when the manifold pressure (MAP) sensor becomes faulty and starts to malfunction.
What is a MAP sensor?
The MAP sensor of the manifold absolute pressure sensor is among the main sensors that are present inside the electronic control unite of the combustion engine. Typically, the MAP sensors are present in the fuel injected engines. The MAP sensor is responsible for generating and transmitting the sensed information on the instantaneous manifold pressure to the electronic control system of the engine. The control unit then uses the computerized approach and the stoichiometric applications to manipulate and interpret the sensed data to determine the air density and the air mass flow rate of the engine.
These parameters are essentially important for the optimal engine performance as they can help the engine system determine the acute fuel metering to accomplish optimum combustion. As a result, it helps the engine control unit to automatically regulate the precise timing of the ignition which can improve the engine performance and fuel efficiency.
The MAF or mass airflow sensors can also be used to sense and record the information on the intake airflow of the engine in the fuel injected engines in combination with the MAP sensors. The data that is generated by the MAP sensors can be transformed into air mass data with the speed density approach. The data from other sensors are also used to carry out these calculations. For instance, the control unit may use the data generated by other sensors such as the air temperature and RPM to calculate the air mass flow rate and the air density as these are the dependent factors.
Faulty Manifold Pressure Sensor Symptoms
Any problem with the manifold pressure sensor (MAP) results in improper combustion which can cause damage to the engine and disrupt the performance. Here are some common symptoms you will experience if you have a damaged manifold absolutely pressure (MAP) sensor.
|Bad MAP (Manifold Pressure Sensor)||Increased Emission Level|
Fail to Pass Emission Test
Bad Engine Performance
Ping or Knocking Noise from Engine
Car Fails to Start
|Dirty MAP sensor |
Faulty MAP Sensor
Faulty MAP Sensor Wirings
|Clean MAP Sensor |
Replace MAP Sensor
Repair Faulty Wirings
Increased Emission Level
When the manifold absolute pressure (MAP) sensor is damaged, it can send an incorrect signal to the powertrain control module (PCM) indicating that there is a high load on the engine. This will cause the PCM to release extra fuel into the cylinder and also release emission of gasses such as carbon monoxide.
Fail to Pass Emission Test
One of the simplest way to determine if you have a faulty MAP sensor is to take your car for an emission test. A vehicle emission test will find out if the car is producing an excessive amount of carbon monoxide and hydrocarbon which will help in determining that there is some problem with the MAP sensor.
Bad Engine Performance
A faulty manifold pressure sensor which measures low intake manifold pressure will transfer this information of low engine load to the PCM. As a result, the PCM will reduce the amount of fuel which is to be injected into the engine. In such case, you will notice an improvement in the fuel efficiency, however, there would be a significant drop in the performance.
Ping or Knocking Noise from Engine
Due to a damaged MAP sensor, the engine sometimes runs lean and the spark plugs even fire quicker than they should normally. This can result in detonation which produces a pinging or a knocking sound. The detonation can prove to be fatal as well and will require you to rebuild the engine.
A malfunctioning map sensor causes the RPM to drop significantly which makes the vehicle surge at low speed. Turning on the air conditioning system will make the situation worse and the engine will die out suddenly.
Car Fails to Start
A faulty MAP sensor will also cause problems when starting the car. The vehicle’s onboard computer uses the MAP sensor to determine atmospheric pressure prior to starting the engine. An incorrect reading may cause a small amount of fuel to be delivered to the engine and as a result, the engine may not start at all.
Where is the MAP sensor located?
Usually, in most vehicles, the MAP sensor is installed within the intake manifold, air cleaner, firewall, under the dash or the fender wall. It may be located below the headlight assembly of the passenger side in the outlet flange of the intercooler. Basically, the map sensor location depends on the design of your vehicle, and its best to refer to the service manual for finding the location of MAP sensor in your vehicle.
Cleaning the MAP Sensor at Home
You can visit an auto specialist for MAP sensor servicing or you can perform the same procedure at home as well with the following steps.
• Owner’s manual
• Electric Part cleaner
• Cleaning Rag
• Socket Wrench
Step 1: Locating the Sensor
For newbies, locating the MAP sensor can be a tough job which is why it is useful if you have the vehicle’s owner manual. You can easily find the location of each sensor including the MAP sensor from the owner’s manual. In general, the MAP sensor can be found near the intake manifold and remove the wire harness can provide better visibility.
Step 2: Remove the Sensor Plug
Make sure the vehicle is switched off and the keys are not in the ignition to avoid the risk of getting an electric shock. Once the sensor is located, remove its plug then gently squeeze the tab holding the sensor in its place. You might need a screwdriver to remove some screws securing the sensor.
Step 3: Cleaning the Sensor
Next step is to clean the sensor gently with an electric parts cleaner. You can easily find an electric parts cleaner at an auto store. Spray the cleaning solvent on a clean cloth and gently rub around the sensor.
Step 4: Let it Dry
Once you are done with the cleaning, leave the sensor to dry and ensure that no liquid residue is present. When you are sure that the MAP sensor is fully dry, install it back into the place and attach the screws and the plug. Close the hood and you are done.
MAP Sensor Replacement Cost
The average cost for MAP sensor replacement is around $120 and $190. The labour cost comes around $30 and $70 while the sensor itself costs between $100 and $120 depending on the model and make. You can also perform the replacement procedure at home, however, the process is risky and you may end up damaging some other component. It is advisable to take the cost estimation from a number of auto specialists and choosing the best one.
Replacing the MAP sensor
A bad or failed MAP sensor can cause you to fail the emission test and lose more money on the extra fuel your vehicle will consume in the long run. Here is a brief account on the step by step guide for replacement of the MAP sensor of your vehicle.
- Make sure you have all the tools with you
- Keep the service manual with yourself
- Locate the MAP sensor that you need to replace by referring to the service manual
- Use the pliers to remove the clamps that are holding it
- Remove all the connections and electrical wires from the sensor
- Remove all the bolts that are holding the MAP sensor on the engine
- Remove the sensor after it is detached
- Match the sensor with the new one
- Replace the sensor in the right place
- Replace the bolts and clamps to hold the sensor on its right place
- Replace all the electrical wires and connections back to the sensor
- Replace the vacuum hose line. (If fitted on the vehicle)
- Take a test drive to make sure that the problem is fixed.
- If the problem persists, take your vehicle to a mechanic.
Diagnosing a Bad MAP sensor
The diagnosis of the bad or failed MAP sensor can be performed by first observing the symptoms that are expressed in your vehicle and then carrying out a physical test as a diagnostic procedure. To do that, here is a brief step by step guide that you can follow in order to check, test and diagnose if the MAP sensor of your vehicle has gone bad.
- Check if the engine of your vehicle is experiencing misfires and shakes
- Check if the check engine light is turned on.
- Observe if your engine is pinging.
- See if the acceleration of your engine is affected.
- See if you are having any problems while starting the engine of your vehicle
- Check if your car is surging or dying out
- Observe if your vehicle’s mileage and fuel efficiency is significantly affected
- See if your vehicle is frequently going on a limp-home mode feature.
- The tune-up of your vehicle did not help in fixing the lousy gas mileage
- If these symptoms are noticeable, carry out a diagnostic test in the following way:
- Locate the MAP sensor of your engine by checking yourself or referring to the service manual of your vehicle
- Make sure that the vacuum hose that is attached to the MAP sensor is properly attached and it is in good condition. make sure that there are no obstacles and remove if there are any. (On some cars, some MAP sensors are fitted directly to the manifold)
- Check to see if the connections and the electrical wires are in good condition.
- Determine the frequency type, voltage and the type of MAP sensor that is installed in your vehicle by checking yourself or referring to the service manual provided by the manufacturer.
- For a voltage type MAP sensor, you will use the voltmeter
- For the frequency type MAP sensor, you will be using the tachometer for the diagnosis.
- Remove the electrical connection from the MAP sensor and turn on the ignition without starting the engine
- Connect the positive probe of the voltmeter to the reference wire and negative one to the ground
- The correct readings should be 5 volts on the power wire(also refer to the service manual to make sure about your vehicle.)
- If there is a problem, install everything that you removed and take your vehicle to the mechanic for advanced diagnosis.
- For the frequency type MAP sensor, you will use a tachometer with the voltmeter.
- Attach a hand vacuum pump after removing the vacuum hose from the sensor
- Turn on the ignition without starting the engine
- At 0 in-Hg vacuum pressure, the voltage readings should be between 4.5 to 5 volts
- On 5 in-Hg vacuum pressure, the voltage reading should be close to 3.75 volts
- On 20 in-Hg vacuum pressure, the voltage reading should be around 1.1 volts.
- Make sure that you use the service manual to see if your vehicle uses the same readings.