With 4L80 Automatic Transmission

Code 34 Manifold Absolute Pressure Sensor Circuit:

Wiring For Diagram For Code 34 Manifold Absolute Pressure Sensor Circuit:

CODE 34 - MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT

CIRCUIT DESCRIPTION:

The manifold absolute pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The PCM receives this information as a signal voltage that will vary from about 1 to 1.5 volts at idle to 4 to 4.5 volts at wide open throttle.

If the MAP sensor fails the PCM will substitute a fixed 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. Code 34 will set when:

^ When engine is less than 1200 rpm.
^ Manifold pressure reading less than 14 kPa, conditions met for 1 second or
^ Engine is greater than 1200 rpm.
^ Throttle angle over 21%.
^ Manifold pressure less than 14 kPa, conditions met for 1 second.

2. Jumpering harness terminals "B" to "C" will determine if the sensor is at fault, or or if there is a problem with the PCM or wiring.

3. The "SCAN TOOL" may not display 5 volts. The important thing is that PCM recognized the voltage as more than 4 volts, indicating that the PCM 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 PCM as an indication of vehicle altitude. Comparison of this reading with known good vehicle with the same sensor is a good way to check the accuracy of a suspected bad sensor. Readings should be the same +/- .4 volt.

Check all connections.
Disconnect sensor from bracket and twist sensor connections. Output changes greater than .1 volt indicates a bad connector or connections. If OK, replace sensor.