DTC 34

Chart - Code 34 Mass Air Flow Sensor Circuit:

Wiring Diagram for Mass Air Flow Sensor Circuit:

CODE 34


MASS AIR FLOW (MAF) SENSOR CIRCUIT (GM/SEC LOW)


Circuit Description:


The mass air flow (MAF) sensor measures the flow of air which passes through it in a given time. The ECM uses this information to monitor the operating condition of the engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicates 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 of the following conditions exists:

Engine running.
No MAF sensor signal for 1.5 mS.
Above conditions for over 4 seconds.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. This step checks 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 CKT 492 or poor connection.

3. Verifies that both ignition voltage and a good ground circuit are available.

Diagnostic Aids:

An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation, or a wire broken inside the insulation.


Check For:


Poor connection at ECM pin "YD10". 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 wires, 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.