DTC 31

Data Trouble Code No. 31 - Volume Air Flow Meter Signal

Detecting Condition

The following conditions are met:
- No Volume Air Flow Meter signal to Engine Control Module for 2 seconds when engine speed is above 300 rpm.
- Engine stall.
or
- No Volume Air Flow Meter signal to Engine Control Module for 5 seconds or more when engine speed is above 300 rpm.

Trouble Area

- Open or short in Volume Air Flow Meter Signal circuit.
- Volume Air Flow Meter.
- Engine Control Module.

Malfunction Indicator Lamp

Normal Mode On
Test Mode NA

Karman Vortex:

Code 31 Description:

Circuit Description
When a pillar (Vortex generating body) is placed in the path of a uniform flow, vortices called Karman-Vortex are generated downstream of the object. Using this principle, a vortex generator is placed inside the volume air flow meter. By measuring the frequency of the vortices generated, the engine control module can determine the volume of air flowing through the volume air flow meter. The vortices are detected by their exerted pressure on thin metal foil (mirror) surfaces and a light emitting element and light receptor (LED and photo transistor) positioned opposite the mirror which senses the vibrations in the mirror optically. The engine control module uses these signals mainly for calculation of the basic injection volume and the basic ignition advance angle.

Code 31 Diagnostic Chart:

Diagnostic Chart

Code 31 Circuit Diagram:

Circuit Diagram

Code 31 Inspection Procedure:

Code 31 Inspection Procedure Page 2:

Inspection Procedure