Description of On-Board Diagnostics

ON BOARD DIAGNOSIS-II SYSTEM (OBD-II)




THE RELATIONSHIP BETWEEN DTC, MIL AND DRIVING PATTERN
Two Trip Detection
- When the same malfunction is detected and maintained during two sequential driving cycles, malfunction indicator lamp (MIL) will automatically light.
- MIL will go off automatically after 3 sequential driving cycles without the same malfunctions re-occuring.

One Trip Detection
- After the ECM first detects a malfunction, a diagnostic trouble code (DTC) is recorded when the engine is restarted and the same malfunction is re-detected. However, for misfire and CKP sensor, diagnostic trouble codes are recorded on the first detection of the malfunction.

DTC Storage
- After recording the diagnostic trouble code, if the ECM does not re-detect the malfunction for 40 driving cycles, the diagnostic trouble code will be erased from the ECM memory.

NOTE:
1) A "warm-up cycle" means sufficient vehicle operation such that the coolant temperature has risen by at least 40 degrees Fahrenheit from engine starting and reaches a minimum temperature of 160 degrees Fahrenheit.
2) A "driving cycle" consists of engine start-up, vehicle operation beyond the beginning of closed loop operation.

MALFUNCTION INDICATOR LAMP (MIL)




An On Board Diagnostic lamp (MIL) comes ON to notify the driver that there is a problem in the vehicle. However the MIL will go OFF automatically after 3 sequential driving cycles without the same malfunction.

MIL Bulb Check
Immediately after the ignition switch is turned on (ON position), the malfunction indicator lamp is lit continuously to indicate that the malfunction indicator lamp operates normally.

MIL Related Systems and Components
- Catalyst
- Fuel system
- Mass Air Flow Sensor
- Intake Air Temperature Sensor
- Engine Coolant Temperature Sensor
- Throttle Position Sensor
- Upstream Oxygen Sensor
- Downstream Oxygen Sensor Heater
- Downstream Oxygen Sensor
- Upstream Oxygen Sensor Heater
- Injector
- Misfire
- Crankshaft Position Sensor
- Camshaft Position Sensor
- Evaporative Emission Control System
- Vehicle Speed Sensor
- Idle Control Valve
- Power Supply
- ECM
- MT/AT Encoding
- Acceleration Sensor
- MIL "ON" Request Signal
- Power Stage
- Canister Close Valve
- Fuel Tank Pressure Sensor

SELF-DIAGNOSIS
The ECM monitors the input/output signals (some signals at all times and the others under specified conditions). When the ECM detects an irregularity, it stores the diagnostic trouble code, and outputs the signal to the self-diagnosis output terminal. The diagnosis results can be retrieved and read with a Generic Scan Tool (GST). Diagnostic trouble code (DTC) will remain in the ECM as long as battery power is maintained within 40 driving cycles. The diagnostic trouble code will however, be erased if the battery negative terminal or the engine control module (ECM) connector is disconnected, the codes are erased by a Generic Scan Tool, or the malfunction(s) do not repeat within 40 driving cycles.