DTC 33

Code 33 Chart:

Code 33 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Mass Air Flow (MAF) Sensor measures the flow of air entering the engine. The sensor produces a frequency output between 32 and 150 hertz (3 gm/sec to 150 gm/sec.). A large quantity of air movement (high frequency) through the MAF sensor indicates acceleration, and a small quantity of air movement (low frequency) indicates deceleration or idle. This information is used by the Electronic Control Module (ECM) for fuel control and is converted by a "Scan" tool to read out the air flow in grams per second. A normal reading is about 4-7 grams per second at idle and increases with rpm.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

Code 33 will set if:

^ Ignition "ON" and air flow exceeds 20 gm/sec.

OR

^ Engine is running at less than 800 rpm.
^ Throttle Position Sensor (TPS) is 10% or less.
^ Air Flow greater than 150 grams per second (high frequency).
^ All of the above are met for 5 seconds or more.

DIAGNOSTIC AIDS:

^ The "Scan" tool is not of much use in diagnosing this code because when the code sets gm/sec will be displaying the default value. However, the "Scan" may be useful in comparing the signal of a problem vehicle with that of a known good running one. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

Check For:

^ Poor connection or damaged harness. Inspect ECM harness connectors for backed out terminal "B6" for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent test. If connections and harness check OK, "Scan" MAF sensor, while moving related connectors and wiring harness. If the failure is induced, the MAF sensor display will change. This may help to isolate the location of the malfunction.

^ Mis-routed harness. Inspect MAF sensor harness to insure that it is not too close to high voltage wires, such as spark plug leads.