See Figures 1 and 2
The Manifold Absolute Pressure sensor, or MAP sensor is mounted on the throttle body. It measures the changes in intake manifold pressure, which result from the engine load and speed changes, and converts this to a voltage output.
A closed throttle on engine coastdown will produce a low sensor output, while a wide-open throttle will produce a high output. This high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100 percent of the outside air pressure is measured.
The MAP sensor reading is the opposite of what you would measure on a vacuum gauge. When manifold pressure is high, vacuum is low.
The PCM sends a 5 volt reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the the manifold pressure. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires less fuel.
The PCM uses the MAP sensor to control fuel delivery and ignition timing.
See Figures 3 and 4
- Backprobe with a high impedance voltmeter at MAP sensor terminal Nos. 1 and 3.
- With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.
- If the voltage is not as specified, either the wiring to the MAP sensor or the PCM may be faulty. Correct any wiring or PCM faults before continuing test.
- Backprobe with the high impotence voltmeter at MAP sensor terminal Nos. 1 and 2.
- Start the vehicle and verify that the sensor voltage is 0.5-1.8 volts with the engine at a normal idling speed.
- Verify that the sensor voltage reaches 3.9-4.8. volts at Wide Open Throttle (WOT).
- If the sensor voltage is not as specified, check the sensor and the sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be faulty.
Removal & Installation
- If the MAP sensor is mounted on the front of the throttle body, the throttle body must first be removed from the engine.
- If the sensor is mounted on the side of the throttle body, the intake air tube must first be removed.
- Remove the two sensor mounting screws and carefully pull the sensor away from the throttle body. Be careful not to lose the rubber L-shaped fitting that attaches the sensor to the throttle body.
- Install rubber L-shaped fitting to the sensor.
- Place the sensor into position being careful to guide the fitting onto the throttle body nipple.
- Install the sensor mounting screws. Tighten the screws to 25 inch. lbs. (3 Nm).
- Install the intake air tube or the throttle body as necessary.