Powertrain Controls - ECM/PCM

Code Chart 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 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. If MAF sensor signal frequency is too low and DTC 34 is set, a substitute value for airflow is calculated based on engine rpm, TP sensor, and IAC motor position.

DTC 34 will set when of the following conditions exists:

^ Engine running.
^ No MAF sensor signal for 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 "YF10." 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.