DTC 34

Code 34 Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION:

The Manifold Absolute Pressure (MAP) Sensor responds to changes in manifold pressure (vacuum). The Electronic Control Module (ECM) receives this information as a signal voltage that will vary from about 1 to 1.5 volt at idle (high vacuum) to 4-4.5 volts at wide open throttle (low vacuum).


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 34 will set if:

^ Engine speed is less than 600 rpm.
^ Code 21 not detected.
^ Manifold pressure less than 13 kPa
^ Conditions met for 1 second
OR
^ Engine speed is greater than 600 rpm.
^ Manifold pressure less than 13 kPa
^ Throttle angle greater than 20%
^ Conditions met for 1 second

2. This tests to see if the sensor is at fault for the low voltage, or if there is a ECM or wiring problem.

3. This simulates a high signal voltage to check for an open in CKT 432. If the test lite is bright, CKT 432 is shorted to ground. If scan reads 4+ volts, CKT 474 can be checked @ terminal "C", it should be 5 volts.


DIAGNOSTIC AIDS:

An intermittent open in circuits 432 or 474 will result in a Code 34.

^ An intermittent on circuit 432 or circuit 474 can cause a Code 34. With the ignition "ON" and the engine "OFF," the manifold pressure is equal to the atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of altitude.


^ Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same +/- 0.4 volts. Also CHART C-1D can be used to check the MAP sensor. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.



^ Make sure electrical connection remains securely fastened. Check all connections. Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than 0.1 volt indicate a bad connector or connection. If OK, replace sensor. Refer to CHART C-1D, MAP sensor voltage output check for further diagnosis