Manifold Pressure/Vacuum Sensor: Testing and Inspection

Checking Pressure Sensor And Circuit:

Output Voltage:

OUTPUT VOLTAGE CHECK
- Remove ECM.
- With connector connected to ECM, connect digital type voltmeter as shown and check that ECM supply voltage 4.75 - 5.25V is applied to connector terminal B1.
- Check output voltage at connector terminal B2. Note that it varies with atmospheric pressure and altitude.
- Also, start engine, if it can, and check if output voltage varies.
- If check result is not satisfactory in previous steps, check pressure sensor and its circuit according to Code No. 31 Diagnostic Flow Chart.


NOTE: If output voltage does not vary when engine is started, it is possible that vacuum hose and/or filter are clogged. Clean them.
Another possibility is that filter in pressure sensor is clogged from freezing. If it is suspected, leave it at room temperature (20° C, 68° F) for a while and recheck.

- Upon completion of checking, install ECM.

Checking Pressure Sensor:

Pressure Sensor Output Voltage vs. Pressure Specification:

PRESSURE SENSOR INDIVIDUAL CHECK
- Disconnect pressure sensor vacuum hose from filter.
- Disconnect pressure sensor connector.
- Remove pressure sensor.
- Arrange 3 new 1.5V batteries in series and connect its positive terminal to "VIN" terminal of connector and negative terminal to "Ground" terminal. Then check voltage between "Vout" and "Ground".

- Also, check if voltage reduces when vacuum is applied up to 40 cmHg by using vacuum pump.

CAUTION: As connection to wrong terminal will cause damage to pressure sensor, make absolutely sure to connect properly as shown.

- If check result is not satisfactory, replace pressure sensor.
- Install pressure sensor and connect vacuum hose securely.
- Connect pressure sensor connector securely.