Q:

What are some tips for troubleshooting the GM manifold absolute pressure sensor?

A:

Quick Answer

Troubleshooting the General Motors manifold absolute pressure or MAP sensor can be done accurately with the use of a mutlimeter and a vacuum pump. Symptoms of a MAP sensor problem that require troubleshooting include specific codes displayed on the instrument panel's check engine light, hard starts, black smoke from the tailpipes, rough idling, lack of engine power and deteriorating gas mileage.

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Full Answer

Diagnostic trouble codes on display at the check engine light in case of MAP sensor problems include P0106, P0107 and P0108 for GM vehicles 1995 and above with on-board diagnostics or OBD II and 33 or 34 for pre-1995 GMs with OBD I.

To use the multimeter to troubleshoot the MAP sensor, disconnect the sensor from the intake manifold, and connect the vacuum pump to the sensor's nipple. If you had to disconnect the electrical connector from the sensor to remove it, reconnect them.

Put your multimeter in volts DC setting. The MAP sensor has three wires connected to it — one gray, one green and one black. Probe the green middle wire. Make sure the MAP sensor is connected to its three-wire connector while doing this.

Connect the black multimeter test lead directly to the car battery's negative terminal. Insert the car key into the ignition and turn it to just before the engine starts. The multimeter should read 4.7 volts DC.

Use the vacuum pump to apply vacuum to the sensor. The multimeter should display the following voltage values according to vacuum strength: 0 in. Hg, 4.7 volts; 5 in. Hg, 3.9 volts; 10 in. Hg, 3.0 volts; and 20 in. Hg, 1.1 volts.

If the multimeter registered these values, this means the MAP sensor is functional and not the cause of the problem. However, if the multimeter voltage did not change, this confirms that the sensor is damaged and should be replaced.

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