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 (high frequency) indicates acceleration, and a small quantity (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.

The MAF sensor is powered up by the MAF sensor relay and the sensor should have power supplied to it anytime the ignition is "ON".

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.

1. Code 33 will set if:

^ Ignition "ON" and air flow exceeds 20 gm/sec. OR engine is running at less than 1300 rpm.
^ Throttle Position Sensor (TPS) is 8% or less.
^ Air Flow greater than 20 grams per second (high frequency).
^ All of the above are met for 2 seconds.

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.