1987 Models
Code 34 indicates the ECM has seen the following:
- Pressure outside a specified voltage range (seen by ECM as voltage at terminal "20").
- Engine RPM less than a given value.
- Engine at operating temperature.
- All the above for a time greater than specified.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart.
- This tests output of sensor at idle to determine if sensor is within specification. Normal sensor will read .59-.64 volts with key in the "ON" position and engine not running.
- Signal voltage should read over 2 volts with engine idling with a minimum of 15 in. Hg vacuum.
- If voltage reads below 2 volts and adequate vacuum was available, the VAC sensor is faulty.
- If voltage remains over 0.5 volts with the sensor harness disconnected the fault is in the harness or ECM. Low voltage indicates a faulty vacuum sensor.
- If voltage remains low when harness terminals B and C are jumpered together the faulty is in the harness or ECM. High voltage indicates a faulty vacuum sensor.