DTC 34

Chart - Code 34 Mass Air Flow Sensor (Signal Frequency Low):

Wiring Diagram for Mass Air Flow Sensor.:

CODE 34 - MASS AIR FLOW (MAF) SENSOR (GM/SEC LOW)


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 !he 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



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, see DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED (rough, unstable, incorrect idle, or stalling.). If the idle improved with the sensor disconnected, replace it. Code 34 could also result from a dirty or misadjusted throttle body.


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

3. With engine running and MAF sensor disconnected probe harness terminal "E" (CKT 993) with a test light to ground. Light should be bright which indicates proper voltage (12 volts) available to MAF sensor.

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 a potential short to ground. Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED. Code 34 could also result from a dirty or misadjusted throttle body.