How to Diagnose A Bad MAP Sensor? | What are Signs of Bad MAP Sensor?

A MAP sensor (manifold absolute pressure sensor) is one of the most important parts of your vehicle engine. A MAP sensor, or manifold absolute pressure sensor, is a type of engine sensor that measures the amount of air pressure present in a vehicle’s intake manifold. As your MAP sensor goes bad, it affects your vehicle’s air-fuel ratio. This article explains the working, symptoms, and causes of a bad MAP sensor.  

What is a MAP Sensor?

The manifold absolute pressure sensor (MAP sensor) is part of an internal combustion engine that is used to measure air pressure in the intake manifold.

MAP sensor

Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to your car’s powertrain control module (PCM).

The PCM utilizes the data of MAP sensor data to calculate air density and adjust different engine parameters, such as air-fuel mixture, ignition timing, and fuel injection, to improve engine emissions, fuel efficiency, and performance.

A fuel-injected engine may also use a mass airflow sensor (MAF sensor) to calculate the intake airflow instead of a MAP sensor.

By exactly gauging the air pressure in the intake manifold, the MAP sensor assists the engine management system to ensure the best suitable combustion settings under different loads and operating conditions. This improves engine performance and fuel economy and reduces emissions.

Symptoms Of A Bad MAP Sensor

As the MAP sensor goes bad, it produces one  or more of the below-given signs:

  1. Check engine light
  2. Rich air-fuel mixture
  3. Lean air-fuel mixture
  4. Stalling
  5. Increased emission level
  6. Engine misfiring
  7. Failed emissions test
  8. Bad engine performance
  9. Rough Idle
  10. Backfires
  11. Hard starting condition
  12. A change in the fuel economy

1) Illuminated Check Engine Light

The illuminated check engine light is one of the first symptoms of a bad MAP sensor.

The powertrain control module (PCM) constantly monitors all your car’s sensors while driving the car. If one of these sensors goes bad then the PCM triggers the check engine light on the vehicle dashboard to alert the driver about the issue.

Therefore, when your manifold absolute pressure sensor sends the wrong information to the PCM, the check engine light will appear on your dashboard.

check engine light

Your PCM may also trigger a trouble code such as P0106, P0107, or P0133 along with the check engine light.

Read More: Why is Check Engine Light Flashing?

2) Rich Air-Fuel Mixture

The main function of the MAP sensor is to measure the correct air pressure in the engine’s intake manifold and send this data to the PCM. The PCM utilizes this data to measure the air-fuel mixture according to the engine requirements.

A faulty MAP sensor sends wrong information to the PCM which may lead to a rich air-fuel mixture. If the air-fuel mix is excessively rich, you may face the following issues:

Air Fuel Mixture

  • Poor fuel economy.
  • Engine stalling
  • Possible spark plug fouling
  • A strong fuel smell from the exhaust system.
  • The catalytic converter may be clogged.
  • A quick accumulation of carbon deposits.

3) Lean Air-Fuel Mixture

The same thing applies the other way around as well. When your MAP sensors don’t send the correct information to the PCM, they may lead to a lean air-fuel mixture.

The air-fuel ratio that is too lean may have even more disastrous consequences:

  • Leaner combustion produces heat, which over time may harm or limit the lifespan of engine components due to excessive heat.
  • Air-fuel combinations that are less rich in oxygen create more toxic byproducts, including carbon monoxide (CO) and nitrous oxide (NOx) (NOx).
  • There is a higher probability of pre-detonation (also known as engine knock). It’s possible to lose a whole engine if a knock occurs when the vehicle is under a heavy load.

4) Engine Stalling 

If your air-fuel mixture is too rich or too lean caused by a faulty MAP sensor, you may notice engine stalling issues. When the engine is running at idle, it is very sensitive, and therefore you may first notice a faulty air-fuel mixture at idle.

engine Stalling due to faulty MAP sensor

When your engine stalls, you should properly inspect all the parts of your vehicle because many other faulty parts may also cause stalling.

Read More: Engine Stalling Symptoms and Causes 

5) Excessive Emissions

Emission Level

When the manifold absolute pressure sensor goes bad, it may send wrong information to the PCM,  indicating a high or low engine load.

Your vehicle engine requires a specific amount of air-fuel mixture to work efficiently and to control exhaust emissions. Even a very small issue with your MAP sensor may disturb the air-fuel mixture, which may increase the emission levels.

6) Failed Emissions Test

Emissions Test

If you live in an area that requires you to pass an emissions test in order for you to register your vehicle, a failed MAP sensor will likely cause your vehicle to fail due to the increased presence of noxious gasses or the check engine light.

 7) Poor Engine Performance

Engine Performance reduction due to bad MAP sensor

As we talked about earlier, a poor air-fuel mixture may lead to poor engine performance. A lean air-fuel mixture is one of the most common causes of poor engine performance. However, a too-rich air-fuel mixture also affects the performance of the engine.

However, your engine performance may be reduced due to misfires caused by bad MAP sensors.

8) Rough Idle

Rough Idle

The rough idle is also a most common sign of a bad MAP sensor. A damaged or faulty sensor may lead to a poor air-fuel mixture. This poor air-fuel ratio may cause extreme engine shaking when idling or random jumps in idle speed.

Read More: Why a Car Shakes at Idle?

9) Backfires

Backfires due to MAP sensor

Your vehicle engine backfires due to poor combustion of the air-fuel mixture inside the combustion chamber.

When the air-fuel mixture doesn’t properly combust in the engine cylinder, it can enter the exhaust pipe.

As expected, the exhaust pipe can reach extremely high temperatures, which could burn the unburnt air-fuel mixture inside it. This can lead to loud explosive noises coming from the exhaust pipe, potentially damaging components such as mufflers. In extreme cases, this may even cause a vehicle to catch on fire.

Read More: Pros and Cons of Muffler Delete

10) Hard Starting Condition

Hard Starting Condition due to bad map sensor

When the MAP sensor goes bad, your vehicle will be hard to start. The trip computer of your vehicle relies on the MAP sensor data to gauge air pressure prior to starting the engine.

Ensuring the correct air-fuel mixture during the startup process is crucial for the engine, and an inaccurate reading from a malfunctioning sensor may lead to insufficient fuel delivery. Consequently, the engine might struggle to start or fail to start altogether.

11) Changed Fuel Economy 

Poor fuel economy

A clear change in the fuel economy is one of the clear symptoms of a faulty MAP sensor. When this sensor goes bad, it sends the wrong information to the PCM. When PCM gets wrong information, it may mix more or lower fuel in the incoming air. 

Causes of a Bad MAP Sensor

The MAP sensor of your vehicle may become faulty due to one or more of the following causes:

  • Age of the sensor
  • Normal wear and tear
  • Extreme temperature or vibration
  • Manufacturing faults
  • Vacuum leaks
  • A leak in the vacuum line attached to the MAP sensor
  • Accumulated dirt, debris, or engine oil on the sensor
  • Wrong installation of the sensor 
  • Damaged wires or loose connection connected to the sensor

MAP Sensor Replacement Cost

If your MAP sensor is bad, you need to replace it as soon as possible. The replacement of the MAP sensor is simple and cheap. In fact, most people could probably handle this one in their own garage and save a bunch of money.

The replacement cost of the MAP sensor depends on the vehicle model, the type of brand, and labor costs. The average replacement cost of the MAP sensor is from $60 to $200. In this cost, the labor cost is from $20 to $80, while the sensor itself costs between $40 and $120.

MAP Sensor Location

According to your car’s design, the MAP sensor’s location varies, and it is advised that you read your car’s maintenance manual for the specific location.

The MAP sensor is normally located on or near the throttle body on the intake manifold. This sensor is located in the intake tract just before the turbo on a forced-induction engine.

For each engine, a sealed chamber within the MAP sensor is calibrated to provide the correct amount of vacuum or regulated pressure.

How to Diagnose a Bad MAP Sensor

To diagnose a faulty MAP sensor, follow the procedures outlined below:

  1. Locate your engine’s MAP sensor by verifying yourself or consulting your vehicle’s service manual.
  2. Maintain the integrity of the vacuum hose that connects the MAP sensor to the engine.
  3. To make sure everything is working properly, check the connections and the cables for damage.
  4. Use an electronic cleaner to clean the sensor and verify the readings on your diagnostic scanner.
  5. Take a look at the wiring between the MAP sensor and the PCM.
  6. If the MAP sensor is damaged, it should be replaced; otherwise, the wiring should be repaired.
  7. After repair, perform a test drive to ensure that the new sensor is working efficiently. 

FAQ Section

What does the MAP sensor stand for?

The MAP stands for manifold absolute pressure. The MAP sensors are most commonly used in internal combustion engines.

What is the function of MAP Sensor?

The main function of the MAP sensor is to measure the intake manifold air pressure and send this information to the PCM. The PCM uses this data to calculate air density and determine the engine’s air mass flow rate, which in turn determines the required fuel delivery for perfect combustion.

Can I drive my car with a bad MAP sensor?

A faulty MAP sensor causes the air-fuel mixture to become excessively rich or too lean. It is not advised to drive with a faulty MAP sensor as this may result in performance issues with your engine. Driving slowly to the nearest repair shop is an option if your automobile is operating well.

Does cleaning the MAP sensor work?

MAP sensors don’t have moving components and don’t normally wear out, although cleaning the sensor may be necessary if it is polluted by carbon or other engine deposits. A possible cause of the sensor voltage slowness when pressure changes might be contamination.

How to reset a MAP sensor?

  1. Inspect your MAP sensor and properly clean it. 
  2. Turn on the sensor and detach the battery for 12 minutes before reconnecting it
  3. PCM will be motivated to retrain itself as a result and your sensor will be reset
  4. Perform a test drive to check the sensor performance

Can a car run without a MAP sensor?

Your car’s engine and the catalytic converter wear out more quickly if you don’t have accurate data from the MAP sensor. If you want to extend the life of your vehicle, avoid driving with a faulty MAP sensor unless it is absolutely necessary.

What happens when I drive without a MAP sensor?

When you drive without a MAP sensor, the fuel delivery will be excessive and could cause harm to the engine and exhaust system (catalytic converters). Your vehicle accelerating on the freeway, bogging down, and reaccelerating may sound like fuel starvation. It could be a fuel pump fault or a plugged fuel filter.

Can a bad MAP sensor cause misfire

Yes, a bad MAP sensor can cause a misfire. An incorrect pressure reading from a faulty MAP sensor can lead to improper air-fuel mixture adjustments by the engine control unit, resulting in misfires and poor engine performance.

What does a MAP sensor do?

Fuel efficiency, pollution, and engine smoothness are all maintained by a MAP sensor in an automobile. The MAP sensor tells the engine computer to supply more fuel when the throttle is wide open, and the air rushes into the intake valve.

What happens when your MAP sensor goes bad?

As the MAP sensor fails, it can cause various issues with the fuel system and vehicle performance. An inaccurate reading from the sensor will cause the computer to change the amount of fuel it sends, which can rob the engine of power or cause it to run poorly.

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