How to diagnose bad MAP Sensor? | What are signs of bad MAP Sensor?

A MAP 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 MAP Sensor?

The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an IC engine’s electronic control system.

MAP sensor

Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine’s electronic control unit (ECU). The data is used to calculate air density and determine the engine’s air mass flow rate, which in turn determines the required fuel metering for optimum combustion and influences the advance or retard of ignition timing.

A fuel-injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow.

MAP sensor data can be converted to air mass data by using a second variable coming from an IAT Sensor (intake air temperature sensor). This is called the speed-density method. Engine speed (RPM) is also used to determine where on a look-up table to determine fuel, hence speed-density (engine speed/air density).

The manifold absolute pressure sensor can also be used in OBD II (on-board diagnostics) applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines.

Bad MAP Sensor Symptoms

As the MAP sensor goes bad, it gives one of the below-given symptoms:

  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

1) Check Engine Light

The engine control unit constantly monitors all your car’s sensors while driving the car. If one of these sensors’ values is out of the specified range – the check engine light will show up.

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

check engine light

Common issues include DTC P0106, DTC P0107, DTC P0133, and or for vehicles with a turbocharger/supercharger, DTC P0299.

Read More: Why is Check Engine Light Flashing?

2) Rich Air-fuel Mixture

If the air-fuel mix is excessively rich, the following may occur:

Air Fuel Mixture

  • The fuel economy will suffer.
  • The spark plugs may foul.
  • The exhaust may have a strong smell of gasoline.
  • The catalytic converter could become clogged.
  • Carbon deposits may build up faster.

3) Lean Air Fuel Mixture

If the air-fuel mix is excessively lean, the consequences can be even worse:

  • Leaner combustion is hotter, which could damage or shorten the life of engine components from excessive heat over time.
  • Leaner air-fuel mixtures also produce more harmful emissions, such as carbon monoxide (CO) and nitrogen oxide (NOx).
  • Pre-detonation (also called engine knock) is more likely to occur. If knock happens under load, it could cause a catastrophic failure, costing you the whole engine.

4) Stalling or Rough Idle

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

Many other faulty parts can also cause this, so it should be appropriately diagnosed before you replace your sensor.

Read More: Signs of a bad Knock Sensor

5) Increased Emission Level

If the manifold absolute pressure sensor is damaged, it can send an incorrect signal to the powertrain control module (PCM), indicating a high or low engine load.

Emission Level

The air-fuel mixture needs to be perfect to have a good emission level in your car. Even a slight error with the MAP sensor may cause the fuel mixture to disturb the emission levels.

6) Failed 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.

Emissions Test

 7) Bad Engine Performance

As we talked about earlier, a faulty fuel mixture will cause the engine performance to drop. A lean mixture usually causes decreased engine performance, but it can be caused by a too-rich mixture.

Engine Performance reduction due to bad MAP sensor

As discussed earlier in the article, bad engine performance can also be caused by misfires caused by a bad MAP sensor.

8) Rough Idle

An improper air-fuel ratio may also cause excessive engine vibrations when idling or random jumps in idle speed.

Rough Idle

9) Backfires

Backfires happen when the fuel going through your engine is not combusted properly.

Backfires due to MAP sensor

When the fuel is not ignited in the combustion chamber, it may end in the exhaust pipe. As you may suspect, the exhaust pipe becomes really hot, and this can ignite the air-fuel mixture there.

This will cause loud bangs coming from the exhaust system, and this can actually cause your mufflers, etc., to explode. It can also cause your car to catch on fire if you are unlucky.

10) Hard Starting Condition

A faulty MAP sensor also causes problems when starting the car. The car’s trip computer uses MAP sensors to determine the air pressure before starting the engine.

Hard Starting Condition due to bad map sensor

The engine is very sensitive to the proper air-fuel mixture at the starting moment; therefore, a faulty reading can cause a too small amount of fuel to be delivered to the engine, and as a result, the engine may not start at all.

MAP Sensor Replacement Cost

If you’ve determined your MAP sensor has gone bad, fear not – replacing the sensor should be relatively cheap and simple. 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 varies according to the car model and labor costs. The average replacement cost of the MAP sensor is between $50 and $180. The labor cost is between $25 and $70, while the sensor itself costs between $27 and $110.

The sensor replacement is often relatively easy and something you can do yourself at home on most car models. If you have a little car knowledge, you can save some money by doing it yourself.

MAP Sensor Location

The MAP sensor is typically located on the intake manifold, either next to or on the throttle body itself. The MAP sensor can be found on the intake tract before the turbo on a forced-induction engine. Inside the MAP sensor is a sealed chamber with either a vacuum or a controlled pressure that is calibrated for the engine. 

The position of the MAP sensor depends on your car’s design, and it is recommended that you check the exact position of the MAP sensor in your car in the service manual.

Diagnosing a Bad MAP Sensor

Follow the below-given steps to diagnose a bad MAP sensor:

  1. Locate the MAP sensor of your engine by checking yourself or referring to the service manual of your vehicle
  2. Ensure that the vacuum hose attached to the MAP sensor is connected correctly and is in excellent condition.
  3. Check to see if the connections and the electrical wires are in good condition.
  4. Clean the sensor with an electronic cleaner and recheck the values with your diagnostic scanner.
  5. Test the sensor after these above-given instructions.
  6. Measure the wirings between the engine control unit and the MAP sensor.
  7. Replace the sensor if it is faulty; otherwise, repair wirings.

FAQ Section

Can I drive my car with a bad MAP sensor?

A bad map sensor causes the air-fuel mixture to get too lean or too rich. This can cause your engine to have performance problems, so driving with a bad map sensor is not recommended. If your car is running fine, you can drive slowly to the closest repair workshop.

Does cleaning the MAP sensor work?

MAP sensors contain no moving parts and don’t typically wear out, but cleaning the MAP sensor may be required if it’s contaminated by carbon or other deposits from the engine. If voltage is slow to respond to pressure changes, contamination could be responsible.

How do you reset a MAP sensor?

  1. Check the MAF sensor and clean it out with dry air. 
  2. Put the sensor on and disconnect the battery for 12 minutes and hook it up. This will clear the computer to want to relearn itself.
  3. Drive the vehicle and see what happens.

Can a car run without a MAP sensor?

Your vehicle will not only run less efficiently without the readings from the MAP sensor, but its engine and the catalytic converter may also wear out faster. To keep your ride running smoothly for as long as possible, you should avoid driving with a bad sensor unless it’s an emergency.

What happens when the MAP sensor goes out?

As the MAP sensors fail, they 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.

What does a map sensor do?

A MAP sensor in a car is used to maintain the right combination of acceleration, fuel economy, emissions, and engine smoothness. When the throttle is wide open and the air is rushing into the intake manifold (causing a drop in pressure), the MAP sensors signal the engine computer to send more fuel.

Does the MAP sensor affect idle?

A faulty MAP sensor can cause engine rpm to fluctuate or surge, primarily at idle or low speeds. If you turn on the air conditioning or use the power steering when this happens, the engine can die out. It will usually restart, but this condition will worsen and can be dangerous.

What are the signs of a faulty MAP sensor?

  1. Check engine light
  2. Hard starting condition
  3. Backfires
  4. Rich air-fuel mixture
  5. Lean air-fuel mixture
  6. Rough Idle
  7. Stalling
  8. Bad engine performance
  9. Increased emission level
  10. Failed emissions test
  11. Engine misfiring
Read More
  1. Different types of IC Engines
  2. What is the function of the O2 Sensor?
  3. Working of Rock Arm
  4. Signs of bad Fuel Pressure Regulator
  5. Signs and Causes of Engine Overheating

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