On Board Diagnostic (OBD): Function

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1999 Volkswagen Jetta, 1998 Volkswagen Jetta, 1997 Volkswagen Passat, 1997 Volkswagen Jetta, and 1996 Volkswagen Passat. However, it is still accessible from the selected car via links, so may be relevant.

The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) for the Turbo-diesel Direct Injection (TDI) system is equipped with Diagnostic Trouble Code (DTC) memory.

If malfunctions occur in the sensors and components that are being monitored, they will be stored in DTC memory along with an indication of the type of malfunction.

Malfunctions that only occur intermittently are identified as "sporadic" malfunctions. The notation "/SP" is displayed on the scan tool, and "sporadic DTC" is added to the print-out. A sporadic malfunction may be caused by, for example, a loose terminal or a temporary open circuit. If a sporadic malfunction does not occur again within 40 warm-up cycles, it will be cleared from DTC memory.

One warm-up cycle is defined as an engine start at engine coolant temperature below 49° C (120°F), and continuous running until engine coolant temperature reaches 71° C (160° F).

NOTE:

For malfunctions that can adversely affect exhaust emission levels, the MIL or Malfunction Indicator Lamp (inset) comes on (lights up).
For malfunctions that influence driveability, the glow plug indicator light flashes.
When malfunctions have been recognized, the stored Diagnostic Trouble Codes (DTC) can be displayed using the VAG1551 or VAG1552 Scan Tool (ST). See CHECK DTC MEMORY (SCAN TOOL FUNCTION 02) .
A print-out is only possible using the VAG1551 scan tool; VAG1552 does not have an on-board printer.
DTC memory must be erased after malfunctions have been eliminated. See ERASE DTC MEMORY (SCAN TOOL FUNCTION 05) .
After erasing DTC memory, the readiness code must be created. See READINESS CODE, SETTING (M.Y. 1997) .

NOTE: The glow plug indicator light has two functions:

Flashing: malfunctions have been recognized that can affect vehicle driveability. Stored Diagnostic Trouble Codes (DTC) can be displayed using the VAG1551 or VAG1552 scan tool. See CHECK DTC MEMORY (SCAN TOOL FUNCTION 02) .
Permanently on (with ignition switched on): Indicates normal glow plug function when starting a cold Diesel engine.

Fig 1: Locating Malfunction Indicator Lamp (Inset)