Balanced air-fuel ratio is the key to better fuel efficiency and engine performance. To achieve the perfect mix, your car’s MAP (manifold absolute pressure) sensor should work flawlessly in sync with your car’s computer.
So what’s a MAP sensor? This sensor sends signals to your engine’s computer based on the vacuum (or lack thereof) within the intake manifold. This helps the computer to decide how much fuel is needed to create the best fuel mixture for your car. If a faulty MAP sensor isn’t detected early on, engine problems may occur. To avoid this, it helps to know these common signs of a bad MAP sensor:
- Check engine light is on. Your car’s engine computer alerts you through your check engine light if your MAP sensor is acting up. When this happens, it’s advisable to check if other sensors in your car are also hinting on a problem with the engine.
- Pinging sounds coming from your engine. Detonation happens when the engine runs lean, producing pinging sounds when you accelerate. When the fuel mixture is lean, it’s usually an indication of a malfunctioning MAP sensor.
- Poor fuel economy. If the MAP incorrectly reads the intake manifold pressure as high, it indicates a high engine load. As a result, fuel injection will increase and your overall fuel economy will fall off.
- Lack of power. On the other hand, if the situation is reversed, meaning, the intake manifold pressure is miscalculated as low, there will be a huge reduction of injected fuel. Less fuel delivered to a high manifold pressure equates to less engine power.
- Failed emission tests. Another consequence caused by a faulty MAP sensor is black exhaust smoke. This is the result of uneven proportion between the amount of injected fuel and the engine load.
How to Check if the MAP Sensor is Bad
Before checking the MAP sensor, inspect your engine parts first. Your MAP sensor works closely with these components and if they are failing, chances are, they are interfering with the MAP sensor’s overall performance.
Check wiring and hoses. They should be intact and properly connected. Search for leaks (e.g. intake manifold vacuum leak or vacuum hose leak). Lastly, get rid of debris and carbon deposits. Once done, do the same visual examination on your MAP sensor.
You can also use a scan tool. Your MAP sensor reading at idle should give you a low output voltage because of low manifold pressure. The reference voltage should be close to 5 volts. If the voltage shown is unusually high or low with your perfectly conditioned MAP sensor (based on your previous visual diagnosis), the erroneous reading is most probably due to other malfunctioning parts. It could be an EGR leak, a clogged converter, or a plugged air filter.
It’s necessary to also pay attention to trouble codes. A faulty sensor displays MAP sensor code P0105 up until P0109 for newer vehicles. For older vehicles, codes 13 – 72 are the indicators. The codes vary depending on the vehicle’s year, make, and model, so do double-check.
After the scan tool test, proceed with bench testing. For this test, you need a hand vacuum pump and a voltmeter. A voltmeter is commonly used by many; however, it’s best to refer to your car’s manual to check the most appropriate device to use for your vehicle.
Begin by turning your ignition key on but do not crank the engine. Put pins (you can use safety pins for this) on your MAP sensor’s wires so the voltmeter probes can be attached to them. Now, attach the hand vacuum pump to your MAP sensor’s vacuum hose. Using the voltmeter, read the voltage output. You should get between 4.5 and 5 volts, with zero inches of mercury (in-Hg) vacuum applied to your MAP sensor. Apply more until 20 in-Hg of vacuum. The voltage output pattern should be dropping until about 1.1 volts. Check your car’s manual for the right specifications and compare them with the values you got—they should be close. If not, that’s a hint that your MAP sensor is broken. Word to the wise: get a replacement as soon as possible.
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