Description of On-Board Diagnostics

PURPOSE
The self-diagnostic system is designed to help technicians fix cars faster. This is done by having the Engine Control Module (ECM) monitor certain input/outputs and store a trouble code if the ECM detects a problem.

OPERATION
The self-diagnostic system has two modes. Mode 1 is the normal operating mode for the vehicle and will turn on the "MALFUNCTION INDICATOR LAMP" (MIL) on if a monitored system has a fault. Mode 2 is used for self diagnostics. Both modes do different things depending whether the engine is running or not.

Mode 1:
Key On, Engine Off:
- This is the "MALFUNCTION INDICATOR LAMP" self-check. If the lamp does not illuminate in this mode check the electrical circuit.

Engine Running:
- This is the normal operating mode. The "MALFUNCTION INDICATOR LAMP" will illuminate only if trouble is found in the following circuits (Diagnostic Trouble Code (DTC) set):

DTC No. Malfunction
12 Mass air flow sensor
13 Engine coolant temperature sensor
14 Vehicle speed sensor
31 Engine Control Module
32 Exhaust Gas Recirculation function
33 Heated oxygen sensor
35 Exhaust Gas Recirculation Temperature sensor
43 Throttle position sensor
45 Injector leak
51 Injector-general


Mode 2:
In this mode a diagnostic trouble code is indicated by the number of flashes from the "MALFUNCTION INDICATOR LAMP" as shown below:

Long (0.6 second) blinking indicates the number of ten digits and short (0.3 second) blinking indicates the number of single digits.

Malfunction Indicator Lamp Code Display Example (Mode 2 Self-Diagnostic Results):

For example, "MALFUNCTION INDICATOR LAMP" flashes once for 0.6 seconds and then it flashes twice for 0.3 seconds. This indicates the number "12" and refers to a malfunction in the mass air flow sensor. In this way, all the problems are classified by their diagnostic trouble code numbers. All diagnostic results will remain in ECM memory.

Key On Engine Off:
- This is the stored codes self-diagnostic mode. Trouble codes extracted in this mode.

Engine Running:
- When the engine is running it is used to monitor the air/fuel mixture and Heated Oxygen Sensor (HO2S) sensor operation.