DTC 34

Code 34 Chart:

Code 34 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The Electronic Control Module (ECM) uses this information to determine the operating condition of the engine, to control fuel delivery. The oil pressure switch or the ECM, through control of the fuel pump relay, will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor. The ECM provides a current limiting 5 volts on the signal line (CKT 998). The MAF sensor then changes the signal by dropping the voltage so that with low air flow the ECM sees a low voltage and a high air flow will cause the ECM to see near the 5 volts supply.

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.

Code 34 indicates ECM has seen low air flow less than 2.5 gm/sec. (low voltage) for one second when:

^ Engine is first started

OR

^ RPM above 600
^ Throttle Position Sensor (TPS) above 6%. To obtain 6%, the engine has to be running at about 2300 rpm in neutral.

1. A Code 34 may be caused by an engine that exhibits a low, rough, unstable or incorrect idle problem. If this condition exists, disconnect the MAF sensor. If the unstable idle still exists, refer to DIAGNOSIS BY SYMPTOM/ROUGH, UNSTABLE, INCORRECT IDLE OR STALLING. If the idle improved with the sensor disconnected, replace it.

2. This test will determine if the conditions still exist to set a code or if the problem is intermittent.

3. With the MAF sensor disconnected, the ECM should see a high signal voltage and set a Code 33. If a Code 34 resets then the wiring or the ECM is at fault.

DIAGNOSTIC AIDS:

A low, rough or unstable idle could result in a Code 34. Also be sure air ducts are tight and not cracked. Check CKT 998 for short to ground. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.