Testing the MAP sensor:
Step 1. Locate the MAP sensor along the firewall or to the right-passenger side of the engine compartment.
Step 2. Check the vacuum hose attached to the sensor and make sure is in good condition and free of obstructions. Also make sure there are no loose wires and the sensor's electrical connector is in good shape.
Step 3. Determine what type of MAP sensor is installed in your vehicle--voltage or frequency type. If you have a voltage type, you will use a voltmeter for this test; if it is a frequency type, you will use a tachometer. Consult your vehicle service manual if you're not sure what type you have.
Step 4. Unplug the electrical connector from the MAP sensor and turn the ignition key on, but do not start the engine. With a voltmeter, measure the reference voltage by touching the reference wire with the meter's positive lead and the negative lead to ground-black wire, which is at the connector's end coming from the computer. If the reference voltage--about 5 volts--is out of specification, you have found the source of the problem. Reconnect the MAP sensor and turn off the ignition key. Take your vehicle to a professional auto electrical shop for further testing.
Step 5. Attach the voltmeter or tachometer negative probe to the ground (black) wire and the positive probe to the signal wire. The sensor's connector should be plugged in. The third wire--the reference wire--produces a steady 5-volt signal only. Consult the wiring diagram in your vehicle's service manual if necessary. You might want to insert pins into the wires to attach the probes to for this test.
Step 6. Disconnect the vacuum hose from the MAP sensor and attach a hand vacuum pump.
Step 7. Turn the ignition key on, but do not start the engine.
Step 8. Read the voltage or rpm. With 0 inches of Mercury (in-Hg) vacuum, you should get between 4.5 and 5 volts, or between 300 and 320 rpm.
Step 9Apply 5 in-Hg of vacuum. You should be reading now about 3.75 volts, or between 275 and 295 rpm.
Step 10. Apply 20 in-Hg of vacuum now. This time you should be reading about 1.1 volts, or between 200 and 215 rpm. Compare your readings with those specified in your vehicle service manual. If the values are out of specification, replace the MAP sensor.
Friday, October 30th, 2009 AT 7:13 PM