DTC 34

- Chart - Code 34 Differential Pressure Sensor (VAC) Voltage Too High Or Low:

- Wiring Diagram for Code 34 Differential Pressure Sensor.:

CODE 34, DIFFERENTIAL PRESSURE (VAC) SENSOR

CIRCUIT DESCRIPTION
Code 34 says that the ECM has seen the following:
a. Pressure outside a specified voltage range (seen by ECM as voltage at Term. "20".
b. Engine RPM less than a given value.
c. Engine at operating temperature.
d. All the above for a time greater than specified.
The VAC sensor is a differential pressure sensor that measures the difference in pressure between atmosphere and manifold. The voltage output is opposite the MAP sensor. The VAC sensor supplies high voltage at high vacuum. High voltage increases spark advance while low voltage reduces advance.

CHART DESCRIPTION
1. Checks output of sensor to determine if sensor is within specification. Normal sensor will read .50 to .64 volts with the key "ON" and engine "OFF".
2. Signal voltage should read over 2 volts, with engine idling, with a minimum of 15" vacuum.
3. If voltage reads above 2 volts and adequate vacuum was available at sensor, the VAC sensor is faulty.
4. If voltage remains low when harness terminals "B" and "C" are jumpered together, fault is in harness or ECM. High voltage would indicate a faulty vacuum sensor.