Code 34- Map Sensor Circuit (3.8L)
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.
Too high a voltage could cause poor performance because of decreased spark advance and wrong fuel control. Too low a voltage could cause detonation because of too much spark advance and poor performance because of poor fuel control.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This step measures voltage output from MAP sensor at ECM.
- Starting the engine should reduce voltage output of sensor 1.2-2.3 volts from what was recorded in Step 1). The sensor has its highest output when manifold pressure (lack of vacuum) is at its highest. The voltage should change as soon as vacuum is changed. A sluggish sensor could cause detonation and/or poor performance. Rapid voltage changes can only be measured with a DVM since Scanner has a time delay.
- If adequate vacuum is available to MAP sensor, disconnecting MAP sensor harness will isolate fault to circuit 452, sensor or ECM.
- This step checks to determine if reason for MAP signal voltage being too low is the circuit or sensor.
- This step determines if circuit from 5-volt reference in ECM and back through terminal "22" is complete. Normal reading would be about 5 volts.