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 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, in calculating fuel delivery. 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, and with the aid of MAF Sensor tester J-36101, or equivalent. Code 34 will set, when either of the following sets of conditions exists:
Engine running and No MAF Sensor signal for 250 m/sec.
OR
Engine running over 1400 rpm.
Throttle Position Sensor (TPS) over 2.5 volts.
Air Flow less than 10 grams per second (low frequency).
Above conditions for over 10 seconds.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. This step checks for a loose or damaged air duct, which could set Code 34 and also checks to see if the Electronic Control Module (ECM) recognizes a problem. A light "OFF" at this point indicates an intermittent fault.
2. A voltage reading at sensor harness connector terminal "B" 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, miss-routed harness, rubbed through wire insulation, or a wire broken inside the insulation.



Check For:
Poor Connection at ECM pin "B-6"; Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire conection.

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.

Miscalibrated MAF Sensor; The Mass Air Flow Sensor may be tested, for being out of specification, by using a MAF Sensor test tool J-36101, or equivalent.