MAP Sensor Testing procedure Chrysler vehicles
Mid 90’s Chrysler vehicles used a Manifold Absolute Pressure Sensor to determine the vacuum and air density of incoming air. When you first turn the key without starting the engine, the computer takes a reading on the MAP to get barometric pressure. Then, when you start the engine and vacuum is applied to the MAP, it can subtracts barometric from manifold vacuum to get a reading on density. As you open the throttle, manifold vacuum decreases. The computer detects the drop in vacuum and increases fuel delivery.
There are 3 wires going to the MAP sensor connector. One outer wire is a 5v reference signal. The computer send the 5volts down the line and monitors the ground return voltage (the other outer wire) at the computer. That way it can tell if there’s a total breakdown in the connection. The middle wire is the one that reports manifold vacuum. Connect the positive lead of a DIGITAL (do NOT use an analog meter to test this—it will fry your computer) to the middle wire and the negative lead to ground. You will have to backprobe the connector or stick a pin in the middle wire to get a reading (seal the hole with nail polish when you finish).
At 0 manifold vacuum, your reading should be 4.5-4.7 volts. Use a hand vacuum pump to slowly apply vacuum directly to the port on the sensor. The voltage should drop steadily as you reach 21” of vacuum, at which point the voltage should read .0-1.1volts. If you don’t get these readings or you get a spike in the readings, you probably have a bad MAP sensor.
To check reference voltage, attach your positive meter lead to one outer wire. It will either read 4.9-5.1 volts (that would be reference voltage), or .050 volts (which would be the ground side of the connector. Both of those readings are with the key on, engine off.
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© 2007 Rick Muscoplat
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Hi : I have a 2002 Toyota RAV4/60K miles and the “check engine light” is on. I took it to two “free” checking places and they both tell me the same problem but suggest two different (expensive) options.
thought I can take your advice before deciding. Thanks, Thommy