Diagnosis System

DIAGNOSIS SYSTEM

1. DESCRIPTION
When troubleshooting OBD II (On-Board Diagnostics) vehicles, a hand-held tester must be connected to the DLC3 (Data Link Connector 3) of the vehicle. Various data in the vehicle's ECM (Engine Control Module) can be then read.




OBD II regulations require that the vehicle's on-board computer illuminates the MIL (Malfunction Indicator Lamp) on the instrument panel when the computer detects a malfunction in:
a. The emission control systems and components
b. The power train control components (which affect vehicle emissions)
c. The computer itself

In addition, the applicable DTCs (Diagnostic Trouble Codes) prescribed by SAE J2012 are recorded on 3 consecutive trips, the MIL turns off automatically but the DTCs remain recorded in the ECM memory.







To check DTCs, connect a hand-held tester to the DLC3. The tester display DTCs, freeze frame data, and a variety of engine data. The DTCs and freeze frame data can be erased with the tester.

In order to enhance OBD function on vehicles and develop the Off-Board diagnosis system, CAN communication is introduced in this system (CAN: Controller Area Network). It minimizes a gap between technician skills and vehicle technology. CAN is a network, which uses a pair of data transmission lines, spanning multiple computers and sensors. It allows a high speed communication between the systems and to simplify the wire harness connection.

Since the CAN communication is equipped in this system, CAN VIM (VIM: Vehicle Interface Module) connecting with hand held tester is necessary to display any information from the ECM on the tester. (Also communication between the hand- held tester and the ECM uses CAN communication signal) When confirm the DTCs and any data of the ECM, connect the CAN VIM between the DLC3 and the hand-held tester.


2. NORMAL MODE AND CHECK MODE
The diagnosis system operates in the normal mode during normal vehicle use. In normal mode, 2 trip detection logic is used to ensure accurate detection of malfunctions. Check mode is also available as an option for technicians. In check mode, 1 trip detection logic is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent problems (hand-held tester only).

3. 2 TRIP DETECTION LOGIC
When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). If the same malfunction is detected during the next subsequent drive cycle, the MIL is illuminated (2nd trip).