Code 34: Map Sensor Circuit

Code 34 says that the ECM has seen the following:

• 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.

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.

1. This step measures the voltage of the MAP sensor as a means of comparison to its known voltage range. A good sensor will fall about mid-way in the voltage range given in the chart. Measurement must be made with the sensor harness connected and jumpers installed.
2. Applying 10 in. Hg to the sensor should reduce the voltage output of the 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 the vacuum is changed. A sluggish sensor could cause detonation and/or poor performance. Rapid voltage changes can only be measured with a DVM.
3. This step checks the voltage at the ECM. Under 2 volts indicates an open in the wire to term. "20". A reading over 2 volts indicates the wiring is okay and fault is in the ECM connections or the ECM.
4. This step checks to determine if the source of low output from the MAP sensor is a ground in the circuit to ECM term. "20" or the ECM. This would be indicated by opening the circuit to term. "20" and noting a voltage increase to normal range when measured at the sensor.
5. This step determines if the circuit from the 5 volt reference in the ECM and back through term. "22" is complete. Normal reading would be about 5 volts.