Is Your Check Engine Light On? How To Test The MAP Sensor

Automotive Blog

Since your car's Check Engine light can be activated by a variety of errors and failures, it can be hard to pin down the direct cause right away. One of the most common sources of Check Engine light trouble is the MAP sensor. MAP is short for manifold absolute pressure, and this sensor monitors the vacuum in the intake manifold compared to the atmospheric absolute pressure. Those readings drive the car's fuel consumption and spark timing. If your MAP sensor isn't functioning properly, it can create an imbalance in the air-to-fuel mixture, which may reduce your engine performance. Here's a look at what you need to know to figure out if the MAP sensor is the problem.

Locate the Sensor

The first step is to locate the MAP sensor. Lift the hood and look along the firewall, which is the back wall of the engine compartment, or along the outside edge of the passenger side of the engine. You'll know the MAP sensor when you see it, because it's a rectangular box that's fitted with a vacuum hose and a three-prong plug.

Check the Plug and Hose

Check the vacuum hose to be sure that it is properly plugged in. It shouldn't be loose where it attaches to the sensor. Then, look at the full visible length of the hose to make sure that there is no obvious damage. If it's damaged, replacing the hose may fix the problem.

If there are no issues with the hose, check the plug for damage. Make sure it's securely attached to the receptacle on the sensor. It should also be free of any exposed or loose wires around the plug.

Test the Sensor Plug

Turn the ignition key to "ON" and leave it in that spot. Don't actually start the car. Trace the wire from the MAP sensor's plug to the car's computer port. Touch the power plug wire where it connects to the computer with the positive lead of your voltmeter, and the black ground wire with the negative voltmeter lead. You should see a consistent reading of approximately five volts if the sensor is working right. If the reading is higher or lower, it's a sign that the sensor is failing.

Understanding how to test the MAP sensor can potentially save you hundreds of dollars in repair labor for trying to replace parts that aren't causing your check engine light failure. If you're uncertain about the testing process or you want expert advice, bring your car to a place like ABS Unlimited Auto Repair so a mechanic can test the car's computer for a trouble code and help narrow down the problem.


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