DTC 34

Code 34 Chart:

Map Sensor Circuit 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 ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS 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.
^ 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:

^ With the ignition "ON and the engine stopped, the manifold pressure will be 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 the accuracy of a suspect sensor. Readings should be the same +/- 0.4 volt.

^ 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.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.