DTC 34

Fig. 039a Code 33 MAP Sensor Circuit:

Fig. 040 Code 34 MAP Sensor Circuit:

CODE 34

MAP SENSOR CIRCUIT

SIGNAL VOLTAGE LOW

(HIGH VACUUM)

2.0L (VIN 1)

FUEL INJECTION (TBI)

Circuit Description: The Manifold Absolute Pressure Sensor (MAP) responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1 to 1.5 volts at closed throttle idle, to 4 - 4.5 volts at wide open throttle.
If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.

Test Description: Numbers below refer to circled numbers on Diagnostic Charts.

1. This step determines if Code 34 is the result of a hard failure or an intermittent condition.
A Code 34 will set when:
MAP signal voltage is too low.
The engine speed is above 1200 RPM.
2. Jumpering harness terminals "B" to "C", 5 volt to signal, will determine if the sensor is at fault, or if there is a problem with the ECM or wiring.
3. The "Scan" tool may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and CKT 432 are OK.

Diagnostic Aids:

The ignition "ON", engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as a reference of vehicle altitude and is known as BARO. Comparison of this BARO reading with a known good vehicle is a good way to check a suspected bad sensor. The reading should be the same plus or minus .4 volts.
A Code 34 will result if CKTs 474 or 432 are open or shorted to ground.
If Code 34 is intermittent, refer to DIAGNOSIS BY SYMPTOM.