On-Board Diagnostic System

View: System Relational Diagram:

OPERATION
When troubles occur in the main input devices or output devices of the engine control system, they are recorded in the memory of the engine control module (ECM).
Failures of each input and output device are indicated and retrieved from the ECM as diagnostic trouble code (DTC) numbers.

NOTE: For input devices, the ECM continuously checks for malfunctions. For output devices, it checks for malfunctions only in a three-second period after the ignition switch is turned to ON.

PRINCIPLE OF CODE CYCLE

View: Code Cycle Break:

1. Code Cycle Break
The time between diagnostic trouble code cycles is 4.0 seconds (the time the lamp is off).

View: Second Digit ("Ones" Position):

2. Second Digit Of Diagnostic Trouble Code (Ones Position)
The digit in the ones position of the diagnostic trouble code represents the number of times the buzzer sounds 0.4 second during one cycle.

View: First Digit ("Tens" Position):

3. First Digit Of Diagnostic Trouble Code (Tens Position)
The digit in the tens position of the diagnostic trouble code represents the number of times the buzzer is on 1.2 seconds during one cycle.

NOTES:
It should also be noted that the light goes off for 1.6 seconds between the long and short pulses of the buzzer.

If more than one failure is present, the code numbers will be indicated in numerical order.