Code 34

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT (SIGNAL VOLTAGE LOW - HIGH VACUUM)
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 about 1 to 1.5 volts at closed throttle (idle) to 4.5 - 4.8 volts at wide open throttle (low vacuum). 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 and the ignition is "ON."
2. Jumpering harness terminals "B" to "C" (5 volts to signal circuit) 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 5 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:

An intermittent open in CKT 432 or CKT 416 will result in a Code 34. With the ignition "ON" and the engine "OFF," 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.
Comparison of this reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be the same + .4 volts. Also CHART C-1D can be used to test the MAP sensor. Refer to "Intermittents" in Section "B".

NOTE: Make sure electrical connector remains securely fastened.

^ Check all connections.
^ Disconnect sensor from bracket and twist sensor By hand (only) to cheek for intermittent connections. Output changes greater than .1 volt indicates a bad connector or connection. If OK, replace sensor.
^ Refer to CHART C-1D, MAP sensor voltage output check for further diagnosis.