CIRCUIT DESCRIPTION:The Mass air Flow (MAF) sensor measure the flow of air which passes through it in a given time. The ECM uses this information to monitor the operation condition of the engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicate deceleration or idle. The MAF sensor produces a frequency signal which cannot be easily measured. The sensor can be diagnosed using the procedures on this chart.
code 34 will set when the following condition exists:
* engine running
* NO MAF sensor signal for 1.5 ms (millisecond)
* above condition for over 4 seconds
TEST DESCRIPTION:Number(s) refer to circled number(s) on the diagnostic chart.
1. This step check to see if ECM recognizes a problem.
2. A voltage reading at sensor harness connector Terminal "A" of less than 4 or over 6 volts indicates a fault in the maf yellow wire circuit or poor connection.
3. Verifies that bolt ignition voltage and a good ground circuit are available.
DIAGNOSTIC AIDS:An intermittent may be caused by a poor connection, mis-routed harness through wire insulation, or a wire broken inside the insulation.
* Poor connection at ECM PIN (yellow wire). Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
* Mis-routed harness inspect MAF sensor harness to insure that it is not too close to high voltage wire, such as spark plug leads.
* Damaged Harness Inspect harness for damage. if harness appears OK, "scan" while moving related connectors and wiring harness. a change in display would indicate the intermittent fault location.
* Plugged Air Intake Filter A wide open throttle (WOT) acceleration from a stop should cause the maf reading on the "scan" to range from about 4-7 gm/sec at idle to 100 or greater at the time of the 1-2 shift. if not, check for restriction.
MASS AIR FLOW SENSOR: The mass air flow (MAF) sensor measures the amount of air which passes through it. The ECM uses this information to determine the operation condition of the engine, to control fuel delivery. A large quantity of air indicates acceleration, while a small quantity indicates deceleration or idle. A Scan Tool reads the MAF value and display it in GRAMS PER SECOND. It should read between 4-7 on a fully warmed up idling engine. Values should change rather quickly an acceleration, but values should remain fairly stable at any given rpm. A failure in the MAF sensor or circuit should set a code 34.
SOURCE: GM SERVICE MANUAL.
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