Powertrain Controls - ECM/PCM

Code 34:

MAF 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 either of the following sets of conditions exists:

^ Engine running.
^ No MAF sensor signal for over 4.0 seconds.

TEST DESCRIPTION: Numbers below refer to circled numbers 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 4.0 or over 6.0 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 ED21 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 acceleration from a stop should cause the MAF reading on the Tech 1 to range from about 4.7 gm/sec at idle to 100.0 gm/sec or greater at the time of the 1-2 shift. If not, check for an intake restriction.