The MAP sensor is an essential part of the engine’s electronic regulatory system. Its primary function is to enable an optimal combustion cycle.
It measures the air pressure inside the intake unit and sends the reading to the powertrain control module (PCM) to regulate the air/fuel mixture ratio.
Since it plays a critical role in the optimal engine operation, it should function correctly. If this sensor fails, it’ll send a false signal to the ECU, mixing an improper air-fuel ratio. This will affect the engine performance.
This article will discuss bad MAP sensors symptoms, common problems, MAP sensor tricks, and how to fix them. Grab a cup of coffee while you have a 5-minute read. Let’s start with how this component works for your better understanding.
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 a MAP Sensor Works?
The car’s MAP sensor is one of the most crucial sections of the vehicle, and its perfect operation is required for the vehicle to function normally.
The manifold absolute pressure sensor operates by changing the electrical resistance and output voltage value due to changes in intake air pressure applied to the silicon chip.
To compute intake air volume, the manifold absolute pressure sensor monitors the intake manifold pressure.
Inside the MAP sensor is a sealed vacuum chamber with either a perfect vacuum or a calibrated pressure, with the intake manifold air pressure to be measured on the opposite side.
A Piezo resistive resistance sensor, which is a tiny flexible silicon chip, is used in the sensor. The silicon chip deflects in response to the intake air pressure, causing a change in resistance as well as output voltage, which is relayed to the car’s electronic control unit (ECU) to modify fuel based on the air.
When the engine is turned on but not yet started, atmospheric pressure exists inside the intake manifold, which aids in estimating air density.
When the engine is started, the pressure inside the intake manifold decreases, and a vacuum is created, and when the driver presses the accelerator pedal, more air enters the manifold, generating high pressure inside the intake manifold.
Because of the high air pressure, the silicon chip flexes upward, causing a change in resistance, and its internal circuitry transforms the change in current into the output voltage value.
As the pressure in the intake manifold raises, the resistance of the resistive element falls, and the voltage signal rises.
Similarly, when the driver takes his or her foot off the accelerator, less air enters and causes low pressure in the intake manifold, allowing the silicon chip to return to its idle state. As a result, you change the silicon chip’s resistance and output voltage.
The ECU uses this voltage change to compute the stoichiometrically correct air-fuel ratio for the car’s engine.
Importance of the MAP Sensor
The MAP sensor provides critical data about the absolute pressure inside the intake manifold. This information allows the ECU to calculate the engine’s load and make necessary adjustments to the fuel injection and ignition timing.
A properly functioning MAP sensor contributes to optimal engine performance, fuel efficiency, and reduced emissions.
MAP sensor location
In most car models, the MAP sensor is located on the intake manifold. It can also be installed on the body of the car on a vacuum hose from the intake manifold.
The MAP sensor’s location will depend on your car’s design, and you should consult the service manual to find the exact position of the MAP sensor in your car.
Bad MAP Sensor Symptoms
The most common symptoms of a bad MAP sensor include poor fuel economy and the check engine light appearing on your dashboard. You might also notice the engine misfiring or stalling, along with a rough idle or difficulty starting the vehicle.
These issues occur because the sensor sends incorrect air pressure readings to the engine control unit, disrupting the air-fuel balance.
Any problem with the manifold absolute pressure sensor (MAP) will result in improper combustion, damaging the engine and disrupting its performance.
Here’s a closer look at the most noticeable signs of a bad MAP sensor and what each one means for your car’s performance.
#1. Check Engine Light.
The engine control unit constantly monitors all the sensors in your car engine while you drive the car. If one of these sensors’ values is out of the specified range, the check engine light will show up.
Therefore, if your MAP sensor sends wrong information to the engine control unit, the check engine light will appear on your dashboard.
#2. Lean Air-fuel Mixture.
The MAP sensor’s primary purpose is to measure the air pressure in the intake manifold to calculate the right air-fuel mixture for your engine. If the sensor is bad, it may cause your engine to get a too lean air-fuel mixture.
Lean fuel mixture can cause many strange symptoms in your engine, which you will find further down in this list.
#3. Rich Air-fuel Mixture.
The same thing applies the other way around as well. If the MAP sensor is bad, it can also send a faulty signal, which will cause the engine control unit to inject too much fuel into the car engine.
A rich air-fuel mixture will not only cause your fuel consumption to go up, but it will also cause performance problems.
#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 problems at the engine’s idle. When the engine is running at idle, it is very sensitive, and therefore you may first notice a faulty air-fuel mixture at idle.
Many other faulty parts can also cause this, so it should be diagnosed properly before you replace the MAP sensor.
#5. Misfires.
Misfires occur when the combustion inside the engine cylinder fails. This can happen due to a wrong air-fuel mixture or a bad spark. A MAP sensor may actually cause the air-fuel mixture to become so bad that you may notice misfires.
You can often recognize misfires by listening to your engine. If you can hear small bumps or if it doesn’t sound like it usually sounds, it may be caused by misfires.
#6. 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 a high or low engine load.
To have a good emission level in your car, the air-fuel mixture needs to be perfect. Even a slight error with the MAP sensor may cause the fuel mixture to disturb the emission levels.
#7. Bad Engine Performance.
As I mentioned earlier, a faulty fuel mixture will cause the engine performance to drop. A lean mixture usually causes decreased engine performance, but it can absolutely be caused by a too rich mixture as well.
Bad engine performance can also be caused by misfires caused by a bad MAP sensor, as discussed earlier in the article.
#8. Backfires.
Backfires happen when the fuel going through your engine is not combusted properly. When the fuel is not ignited in the combustion chamber, it may end up 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.
#9. Hard Starting Condition.
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.
The engine is very sensitive to having the right air-fuel mixture at the starting moment, and therefore, a faulty reading can cause too little fuel to be delivered to the engine. As a result, the engine may not start at all.
#10. Changed fuel consumption.
This is most probably the most understandable if you read everything above in the article. A faulty air-fuel mixture caused by a bad MAP sensor will, of course, also cause the fuel consumption to change.
If you notice that your car requires less or more fuel than before, it can absolutely be caused by a faulty MAP sensor.
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
How Do You Test An MAP Sensor?
How to test a MAP sensor is a simple DIY skill every car owner should know. Let’s see how to carry out the test. The MAP sensor usually connects to the air intake.
Here’s a step-by-step guide on how to test a MAP sensor.
- Depending on your vehicle, disconnect all surrounding components around the MAP sensor to gain full access.
- Disconnect the wiring harness on the MAP sensor.
- Check if there’s any corroded connector pin.
- Test the connectors with a multimeter or voltmeter.
- Connect a lead to the ground and probe the external connector. It should give 5 volts.
- Test the outside terminal for 5 volts and confirm if the car computer is grounding correctly.
How to Diagnose a faulty MAP sensor?
#1. Reading fault codes.
When the MAP sensor malfunctions, an OBD2 scanner can be used to quickly diagnose the problem. It can read the fault codes and monitor the sensor’s data stream, thus rapidly pinpointing the issues with the MAP sensor.
#2. Inspecting the sensor’s appearance.
Check if the sensor’s appearance is damaged, whether there are cracks or detachments in the vacuum hoses. Also, confirm whether the wiring harness plug is firmly connected.
#3. Measuring the sensor voltage.
Turn on the ignition switch (without starting the engine) and measure whether the sensor’s reference voltage (usually 5V) is normal.
How To Fix MAP Sensor?
Here are some elements you should check before bringing your car to an auto shop to replace the sensor.
#1. Hose.
In some cars, a hose links the intake manifold and the MAP sensor. So you should know whether the MAP sensor hose is intact and connected or not.
In addition to checking the sensor hose, check that the port is free of debris and carbon deposits, which can block the hose and result in wrong sensor readings.
#2. Electrical.
Check the wiring and connector. The wiring between the MAP sensor and ECM should be intact. Chafing could result in short circuits and breaks could result in open circuits.
Similarly, the connector should be securely connected, and the pins should be straight and clean. Bent pins and corrosion can cause sensor signal problems.
#3. Sensor.
If the sensor is installed correctly, both to the intake manifold and electrically, use a vacuum gun and a voltage meter or a scan tool to check.
You will have to look up a chart to measure voltage against full vacuum and no vacuum. If the chart gives a result that is not similar to the output, it’s time to replace the sensor.
How To Replace A Bad MAP Sensor?
The steps to replace a failed sensor vary from one vehicle to another. However, some basic procedures are almost the same.
Take these notes below as your reference for the next replacement project. If you have less experience to mechanic self-projects, consult a professional about any details.
- The sensor should be located on the intake manifold, either close to or on top of the throttle body, or on the intake manifold itself.
- Remove any screws or nuts holding the sensor in place.
- Disconnect the electrical connection. Avoid using force since it may contain a locking tab that must be removed before it can be unlatched from the sensor.
- Disconnect the vacuum hose from the sensor. The suction pipe should be replaced with a new hose.
- Examine the distinctions between the new and old sensors.
- Reconnect the suction hose if required.
- Reconnect the sensor’s electrical connection.
- Replace any screws or nuts keeping the sensor in place.
- Check each connection to make sure they are stable.
How much does a MAP sensor 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 MAP sensor usually sits in an easy to reach area, on or near the intake manifold. The sensor itself will cost you anywhere from $30 to $200, depending on your vehicle and if you use OEM or aftermarket parts.
If you go to a mechanic or dealership to have the MAP sensor replaced, tack on another $40 to $60 or so in labor cost.
Even though it should only take a few minutes to replace, most shops usually have a minimum labor charge. This makes DIY replacement the best option in most cases.
Sometimes MAP sensors are connected to the intake manifold via a vacuum hose. If this hose has a vacuum leak, replacing the hose for less than $10 may solve the problem altogether.
Consult a factory-style manual (such as Haynes or Chilton) for information on how to replace a MAP sensor on your specific vehicle.
FAQs.
Q: Can a bad MAP sensor cause limp mode?
There are a few car sensors that control the engine and the transmission, such as the TPS, MAF, MAP, or speed sensors. If any of these sensors fail, it can put your car into limp mode.
The limp mode will limit your vehicle’s functionality. Assistive and frills functions will stop working, and your transmission will not shift to higher gears.
Q: Will a bad MAP sensor throw a code?
A failing MAP sensor will trigger an engine warning light and may throw a diagnostics trouble code. Note that a failing MAP sensor may not throw an error code until it’s completely damaged. A MAP can also fail by being contaminated, damaged, or clogged.
Q: Will a MAP sensor cause stalling?
A defective MAP sensor will send false information to the car computer to change the air-fuel mixture ratio. This will cause rough idling or a lack of engine power.
If the powertrain control module (PCM) permits an inadequate amount of fuel to enter the combustion chamber, there will be a lack of performance. This can also cause engine stalling and hesitation.
Q: Can you drive a car with a bad MAP sensor?
A bad MAP sensor will not only cause a lack of engine performance but its catalytic converter and engine components will wear out.
If you want to enjoy a seamless driving experience, do not run with a bad MAP sensor. Avoid driving with a malfunctioning MAP sensor unless you have emergencies.
Q: Can a MAP sensor cause a no-start?
The vehicle engine control module gauges the atmospheric pressure before starting the engine. The car computer does this with the help of the MAP sensor.
A false reading from the MAP sensor can cause too low or too high fuel to enter the combustion chamber. Both conditions can cause hard starting. In rare cases, it can prevent the vehicle from starting.
Q: Do you have to disconnect the battery to change the MAP sensor?
You can change the MAP sensor without removing the battery terminal. However, it’s recommended to disconnect the battery before replacing the MAP sensor.
This will ensure the car and electrical components are not damaged when you remove the sensor. It will also prevent the car computer from resetting and logging fault codes.
Final words
Several bad MAP sensor symptoms show an engine malfunction. While some symptoms above are likened to your engine components malfunctions, if you detect two or more, inspect your MAP sensor.
Always watch out for these signs early enough to detect and fix the culprit to avoid dropping expensive repair bills on the table. If you suspect a lousy MAP sensor, inspect the sensor or contact an expert mechanic for professional inspection and fixes.