DTC 34

Mass Air Flow Sensor Circuit:

Circuit Description:
The Mass Air Flow (MAF) sensor measures the flow of air which passes through it in a given time. The PCM 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 the following conditions exist:

^ Engine running.
^ No MAF signal for over 4 seconds.

Code 34 Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step checks to see if PCM 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 PCM Pin "BD14 - 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, observe Tech 1 while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

^ Plugged Air Intake Filter - A WOT acceleration from a stop should cause the MAF reading on the Tech 1 to range from about 4.7 at idle to 100 or greater at the time of the 1-2 shift. If not, check for restriction.