The manifold absolute pressure sensor, also known as the MAP sensor, is an integral part of the vehicle’s engine system.
The MAP sensor is found in vehicles with fuel injection and the main function of the MAP sensor is to provide the Powertrain Control Module (PCM/ECM) with information about the pressure in the intake manifold.
Like every sensor in your vehicle, the MAP sensor will wear and tear over time and become damaged, which can lead to incorrect data being transmitted to the engine control module.
This incorrect information can lead to reduced performance, reduced fuel economy and various other consequences.
In this article we discuss some of the key symptoms that occur when the manifold absolute pressure (MAP) sensor becomes defective and begins to malfunction.
Signs of a Bad MAP Sensor
Any problem with the manifold absolute pressure sensor (MAP) will result in improper combustion, which can damage the engine and disrupt performance.
Here are some common symptoms that can occur with a damaged manifold absolute pressure sensor (MAP).
1. Increased Emission Level
If the manifold absolute pressure sensor (MAP) is damaged, it can send an incorrect signal to the powertrain control module (PCM) indicating that there is a high engine load. This causes the PCM to release additional fuel into the cylinder and also emits gases such as carbon monoxide.
2. Fail to Pass The Emission Test
One of the easiest ways to determine if you have a defective MAP sensor is to put your car through an emissions test.
A vehicle emissions test will determine if the car is producing excessive amounts of carbon monoxide and hydrocarbons, which will help determine if there is a problem with the MAP sensor.
3. Bad Engine Performance
A faulty manifold pressure sensor, which measures low intake manifold pressure, transmits this low engine load information to the PCM. As a result, the PCM reduces the amount of fuel to be injected into the engine.
In such a case you will notice an improvement in fuel efficiency. However, there would be a significant drop in performance.
4. Ping or Knocking Noise from Engine
If you have a poor MAP sensor, the engine will sometimes run lean, resulting in combustion failure. This can lead to a detonation that produces a pinging or knocking sound.
The detonation can also be fatal and requires an engine modification.
5. RPM Drops
A defective map sensor causes the RPM to drop significantly due to an incorrect fuel mixture, causing the vehicle to vibrate at low speed. Switching on the air conditioning makes the situation worse and the engine suddenly dies off.
6. Car Fails to Start
A faulty MAP sensor also causes problems when starting the car. The car’s trip computer uses the MAP sensor to determine the air pressure before starting the engine.
A faulty reading can cause a small amount of fuel to be delivered to the engine and as a result the engine may not start at all.
Problem Symptoms Causes Solutions 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
What is a MAP sensor?
The MAP sensor is one of the most important sensors in the electronic control unit of the combustion engine. Normally, the MAP sensors are present in engines with fuel injection.
The MAP sensor is responsible for generating and transmitting to the engine’s electronic control system the information acquired about the current boost pressure.
The control unit then uses the computerized approach and stoichiometric applications to manipulate and interpret the acquired data to determine the air density and air mass flow rate of the engine.
These parameters are essential for optimum engine performance as they can help the engine system to determine the acute fuel dosage to achieve optimum combustion. As a result, it helps the engine management system to automatically control the exact timing of ignition, which can improve engine performance and fuel efficiency.
The MAF or mass airflow sensor, in combination with the MAP sensors, can also be used to capture and record the same information about engine intake airflow in fuel injected engines.
The data generated by the MAP sensors can be converted to air mass data using the RPM density approach. Data from other sensors is also used to perform these calculations.
For example, the ECU can use the data generated by other sensors, such as air temperature and engine speed, to calculate air mass flow and air density, as these are the dependent factors.
Where is the MAP sensor located?
Normally, on most vehicles, the MAP sensor is installed inside the intake manifold, air filter, firewall, or under the dashboard or fender wall. It can be located below the passenger side headlight assembly in the intercooler outlet flange.
The position of the MAP sensor depends on the design of your car and it is recommended that you check the position of the MAP sensor in your car in the service manual.
Cleaning the MAP Sensor at Home
You can visit an automotive specialist for maintenance of the MAP sensors, or you can perform the same procedure at home using the following steps.
• Owner’s manual
• Electric Part cleaner
• Cleaning Rag
• Socket Wrench
Step 1: Locate the Sensor
For novices, locating the MAP sensor can be a difficult task, so it is useful to have the vehicle user manual. You can easily find the position of each sensor, including the MAP sensor, in the vehicle owner’s manual.
In general, the MAP sensor is located near the intake manifold and if you remove the wiring harness, you can see it better.
Step 2: Remove the Sensor Plug
Make sure that the vehicle is switched off and the keys are not in the ignition to avoid the risk of damage to sensitive electrical parts.
Once the sensor is located, remove the connector plug and gently press the tab that holds the sensor in place. You may need a screwdriver to remove some of the screws that hold the sensor in place.
Step 3: Clean the Sensor
The next step is the gentle cleaning of the sensor with an electrical parts cleaner. You can easily find a cleaner for electronic parts in a car dealership. Spray the cleaning agent on a clean cloth and rub gently around the sensor.
Step 4: Let it Dry
When you have finished cleaning, allow the sensor to dry and make sure that there is no liquid residue.
When you are sure that the MAP sensor is completely dry, reinstall it in place and secure the screws and connector. Close the hood and you are done.
MAP Sensor Replacement Cost
The average cost of replacing a MAP sensor is about $120 to $190, labor costs are about $30 to $70, while the sensor itself costs between $100 and $120, depending on the model and brand.
You can also do the replacement procedure at home. However, the procedure is risky and may cause you to damage other electrical components. It is advisable to have the cost estimate prepared by an automotive specialist.
Replacing the MAP sensor
A poor or faulty MAP sensor can cause you to fail the emissions test and lose more money on the extra fuel your vehicle will use in the long run.
Here is some brief step-by-step instructions for replacing your vehicle’s MAP sensor.
- Make sure you have all the tools with you
- Keep the service manual with you
- 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 correct place
- Replace the bolts and clamps to hold the sensor in place
- Replace all the electrical wires and connections 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
Diagnosis of a faulty or failing MAP sensor can be made by first observing the symptoms that are present in your vehicle, and then conducting a physical test as a diagnostic procedure.
For this purpose, here is a brief step-by-step guide that you can follow to check, test, and diagnose if the MAP sensor in 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 whether 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 stalling
- Observe if your vehicle’s mileage or fuel efficiency are significantly affected
- See if your car is frequently goes into limp mode.
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 connected correctly and it is in excellent 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 (but refer to the service manual to check the correct readings for your vehicle)
- If there is a problem, reinstall everything that you removed and take your car 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
- At 5 in-Hg vacuum pressure, the voltage reading should be close to 3.75 volts
- At 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.