Powertrain Controls - ECM/PCM

Code 34 Chart:

MAF Sensor Wiring Diagram:

***UPDATED BY TSB # 92-6E-26 DATED NOVEMBER 1992



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 4 seconds.

NOTE: If the MAF sensor frequency is to low a Code 34 will set, a substitute value for air flow is calculated based on engine rpm, TPS, and IAC valve position.



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.