DTC 34

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from less than 1.0 volt at closed throttle idle, to 4.0-4.5 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 the diagnostic chart.
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.
^ Engine speed below 1200 rpm and/or TPS greater than 20%.
2. Jumpering harness terminals "B" to "C", 5 volts 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 battery voltage. 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
With the ignition "ON" and the 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 an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same ±0.4 volt.

A Code 34 will result if CKTs 474 or 432 are open or shorted to ground.

If CKT 416 is shorted to ground, there may also be a stored Code 22.

If Code 34 is intermittent, refer to Symptoms. Testing and Inspection