Without Speed Density Update

Chart - Code 33 Mass Air Flow Sensor (Signal Frequency High):

Wiring Diagram for Mass Air Flow Sensor Circuit:

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 (mounted on the left shock tower) and the sensor should have power supplied to it anytime the ignition is "ON."

TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart.
1. Code 33 will set if:
- Ignition "ON" and air flow exceeds 20gm/sec. or
- Engine is running 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, It may be useful in comparing the signal of a problem vehicle with that of a known good running one. A MAF sensor may provide an incorrect signal to the ECM if it is contaminated with foreign material or if water droplets collect on the sensor. Check the air filter to assure that it is sealing properly and that it is of the water resistance type. If replacement is required, use the filter specified in owner's manual or with a filter that meets the same specifications. See "DIAGNOSIS BY SYMPTOMS." Testing and Inspection