DTC 34

Code 34 - Mass Air Flow (MAF) Sensor:

Wiring Diagram for Mass Air Flow (MAF) Sensor:

CODE 34 - MASS AIR FLOW SENSOR (MAF) SIGNAL FREQUENCY LOW

Circuit Description:


The MAF sensor measures the flow of air entering the engine. The sensor produces a frequency output between 32 and 150 hertz. A large quantity (high frequency) indicates acceleration, and a small quantity (low frequency) indicates deceleration or idle. This information is used by the 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 5-8 grams per second at idle.

Code 34 will set if:

^ Engine running

^ MAF sensor disconnected, faulty relay, or MAF signal circuit shorted to ground

^ OR

^ Air flow less than 2 grams per second (low frequency).

The "Scan" tool is not of much use in diagnosing this code, but may be useful in comparing the signal of a problem vehicle with that of a known good running one.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. A loose or damaged air duct can set Code 34.

2. Checks to see if ECM recognizes a problem. A light off at this point indicates an intermittent problem.

3. Checks to see if 5 volts reference signal from ECM is at MAF sensor harness connector.


Less than 1 volt indicates a faulty CKT 528, wiring connector, or ECM.

4. Checks continuity of electrical circuit at MAF sensor.

5. Checks for open in 12 volt supply.