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HOMESERVICE MANUALSPONTIAC1983GRAND PRIX BASE, 5.0 HREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 11 (FEEDBACK CARBURETOR TESTS W/CODES)CODE 34: DIFFERENTIAL PRESSURE (VACUUM) SENSOR
1983 Pontiac Grand Prix Base, 5.0 H

Code 34: Differential Pressure (Vacuum) Sensor

1983 Pontiac Grand Prix Base, 5.0 HSECTION Code 34: Differential Pressure (Vacuum) Sensor
WARNING: This page does not describe the selected car, but rather 28 other vehicles, including the 1984 Pontiac Phoenix, 1984 Pontiac Parisienne, 1984 Pontiac Grand Prix, 1984 Pontiac Firebird, and 1984 Pontiac Bonneville. However, it is still accessible from the selected car via links, so may be relevant.

Code 34 says that the ECM has seen the following:

NOTE: The use of 3 jumper wires will be required and can be made using terminal part numbers 12014836 and 12014837.
  • Pressure outside a specified voltage range (seen by ECM as voltage at term. "20").
  • Engine RPM less than a given value.
  • Engine at operating temperature.
  • All the above for a time greater than specified.

The VAC sensor measures the difference in pressure between atmosphere and manifold. The vacuum sensor supplies high voltage at high vacuum. High voltage increases spark advance.

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).
  1. This test checks output of sensor at idle to determine if sensor is within specification. Normal sensor will read less than 1 volt with key "ON", engine "OFF" and over 3 volts with engine idling 15 in. Hg minimum).
  2. Normal sensor will drop below 1 volt with no vacuum.
  3. This test checks for a ground in wire from term. "B" of vacuum sensor to ECM. Line is open if voltage is over 2 volts.
  4. This test checks to see if the fault is in the sensor, the ECM wiring, or the ECM. If the voltage goes over 2 volts with the sensor disconnected, the sensor or sensor connections are faulty.
Fig 1: Code 34: Differential Pressure (Vacuum) Sensor Flow Chart
G9314
RENDER: 1.0x

NO RELATED

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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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