Modern cars are loaded with tons of computers, sensors, and other electronics. When everything is working correctly, these modern electronics can make driving your car far more convenient and efficient. However, many of these electronic components rely on one another to function properly, and if one of them goes bad it can severely hinder the drivability of your car.
The MAP sensor is one such component. If the MAP sensor in your car fails, it can result in a number of undesirable symptoms, including a rough idle, poor fuel economy, a check engine light, and more besides.
In this article, we’ll be covering what a MAP sensor is and what it does, and we’ll be going into more detail on the symptoms of a bad MAP sensor and what you can do to solve this issue.
What Is a MAP Sensor, and What Does It Do?
Despite what you might assume from the name, the MAP sensor has nothing at all to do with your car’s navigation system. In this context, MAP stands for “manifold absolute pressure”, and the purpose of the MAP sensor is to determine how much air is inside the engine at any given time. This helps the ECU (engine control unit) deliver the correct amount of fuel to the combustion chamber.
The MAP sensor is usually located inside or near the intake manifold, although the location may change depending on the specific car you have. If you’re unsure of where the MAP sensor in your car is located, your owner’s manual should have that information available.
It’s also worth mentioning that not all cars have a MAP sensor; most cars you’ll encounter are more likely to use a MAF (mass air flow) sensor instead. As the names imply, the difference between the two sensors is that MAP sensors work by detecting changes in air pressure, while MAF sensors work by detecting changes in airflow.
MAP sensors generally tend to be used on cars with forced induction, because in those cases the air that enters the intake is actually pressurized beyond normal atmospheric pressure. For naturally aspirated cars, it’s far more common to use a MAF sensor.
Some cars actually use both types of sensors, as this can give the ECU a more accurate reading in some cases.
What Are the Symptoms of a Bad MAP Sensor?
If the MAP sensor in your car starts to go bad, the ECU will fail to get an accurate reading of how much air is entering the intake. This could result in the cylinders receiving either too much or too little fuel. In either case, this will have both short- and long-term consequences for your engine.
The symptoms of a bad MAP sensor are fairly similar to the symptoms that you might experience if some of the other components of your fuel system were to fail. While these symptoms don’t necessarily indicate a problem with your MAP sensor, they do indicate that something is wrong with your fuel system in general.
Here are the symptoms you should look out for:
Poor Fuel Economy
This can happen if your MAP sensor fails in such a way that the ECU thinks that the engine is constantly at high load. When this happens, the ECU will advance the spark timing and send way more fuel to the engine than necessary.
This can lead to poor fuel economy since the engine is burning way more fuel than it actually needs. It can also result in detonation, which is when fuel detonates in the combustion chamber after the spark plug fires. This puts a lot of strain on the inside of the combustion chamber and can potentially damage it.
Low Engine Power
On the other hand, if the ECU thinks that the engine load is low thanks to a bad MAP sensor, it will retard the spark timing and send less fuel to the engine.
When this happens, the engine will obviously use a lot less fuel than normal, which may seem like a good thing at first. However, if the engine is receiving way too little fuel, you will end up losing power and be unable to reach high speeds or accelerate quickly enough.
If a bad MAP sensor is making the engine run either too rich or too lean, you’ll likely have problems starting your engine. This happens because if the engine is running lean, it won’t have enough fuel to initiate combustion, and if it’s running rich then there won’t be enough air in the cylinders for the engine to run properly.
If you notice that your car idles roughly or sometimes misfires, this could be a sign of a bad MAP sensor. A running engine needs to receive a specific amount of air and fuel to idle smoothly, and if the engine isn’t receiving enough of either thanks to a fault MAP sensor, you will easily be able to tell by the sound of the idle.
If the MAP sensor is causing your engine to run lean, you may find that it tends to stall at certain points, particularly when accelerating from a stop or when accelerating as part of a passing maneuver.
Check Engine Light
The check engine light activates if the ECU detects that something is wrong. Obviously, the check engine light can come on for any number of issues, but if you see it in conjunction with these other symptoms, it can be a good sign that your MAP sensor is on its way out.
If you have an OBD2 scanner, you can check to see if your computer has logged any error codes related to the MAP sensor. In particular, you should be on the lookout for these codes:
Why Do MAP Sensors Fail?
It’s not too common for the MAP sensor in a car to fail, but it can definitely happen. There can be a few different causes for this.
MAP sensors often contain some kind of hose through which air passes, and if this sensor gets blocked or develops a hole, it can throw off the MAP sensor’s reading. The sensor’s connectors can also be damaged by excessive heat or vibrations from the engine.
If the problem is just caused by a blocked tube, you can probably fix the problem by finding the sensor and removing the blockage, but if the sensor is actually damaged then it will have to be replaced.
Can I Drive With a Bad MAP Sensor?
If you suspect that your car has a bad MAP sensor, you should refrain from driving it until the problem is fixed. You can probably drive to a repair shop with a bad MAP sensor, but you shouldn’t do any more driving than that unless you want to risk damaging your engine or exhaust system.
If your engine is running rich, you run the risk of clogging up your catalytic converter, and if your engine is running lean then there will be more friction than normal occurring within the cylinders, which can cause some components to wear out more quickly.
How to Replace Your Car’s MAP Sensor?
The location of your car’s MAP sensor is going to vary depending on what kind of car you have, so again, check your owner’s manual to find out the exact location. Once you have it, however, the process of replacing it is pretty straightforward.
Here’s how to replace a bad MAP sensor:
- Once you’ve found where the sensor is located, remove any bolts or screws holding it in place.
- Disconnect the sensor from the attached electrical harness. Be careful when doing this, as there may be a tab you need to release before the harness can be removed. Otherwise, you may end up breaking the harness.
- Detach the vacuum hose from the sensor, if applicable. If your sensor does use a vacuum hose, you should replace it as well if you’re going to be replacing your sensor.
- Grab your replacement sensor, and double-check to make sure it’s the same as the one you’re removing. You don’t want to replace your existing MAP sensor with one that is incompatible with your car.
- Connect the new vacuum hose to the new sensor, if applicable.
- Reconnect the wiring harness to the new sensor.
- Screw or bolt the new sensor back into place.
- Double-check that the wiring harness is properly connected and that the sensor is properly screwed into place. If it is, take your car for a test drive and see if you’ve successfully solved the issue.