DTC 34

- Chart - Code 34 MAP Sensor (Voltage Signal Incorrect):

- Wiring Diagram for Code 34 MAP Sensor.:

CODE 34 MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
SIGNAL VOLTAGE LOW - HIGH VACUUM

CIRCUIT DESCRIPTION
Code 34 indicates that the ECM has monitored the following:
a. Pressure outside a specified value range (monitored by ECM as voltage at terminal "20").
b. Engine rpm less than a given value.
c. Engine at operating temperature.
d. 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.

CHART DESCRIPTION
Numbers below refer to circled numbers on the diagnosis chart.
1. This step measures the voltage output from the MAP sensor at the ECM.
2. Starting the engine should reduce the voltage output of the sensor about 1.2 to 2.3 volts from what was recorded in Step 1. The sensor has its highest output when manifold pressure (lack of vacuum) is 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. If adequate vacuum is available to the MAP sensor, disconnecting the MAP sensor harness will isolate the fault to CKT 452, sensor, or ECM.
4. This step checks to determine if the reason for the MAP signal voltage being too low is the circuit or the sensor itself.
5. This step determines if the circuit from 5V ref. in the ECM and back through terminal "22" is complete. Normal reading would be about 5V.