General Diagnosis

Almost all microprocessor-controlled Systems in the car have in-built diagnostic functions, and there are two DLCs in the engine compartment. DLC A has a black casing, DLC B a grey one. Both have black covers.

DLC A is a standard DLC with selector cable, LED and buttons for selecting the different test modes, ABS system diagnosis and fault-tracing uses DLC A.

DTCs posted can be read off manually by counting the number of times the LED flashes or direct in plain text using the ST instead of the DLC.

Please note In some markets, the DLC has no LED or buttons: the ST must be used.

All microcomputer-based systems in the car have diagnostic capabilities to Volvo standards. This includes the ABS system.

The diagnostic system is in two parts:
- self-diagnosis and changing the transmission speed.
- Self-diagnosis means that individual electronic systems run self-test routines while they are switched on and store DTCs for retrieval at a later stage.

Self-diagnosis function:
- Detects and identifies faults in the electronics system.
- Stores the appropriate DTCs for the fault. Up to 3 DTCs can be stored simultaneously.
- Displays coded messages (DTCs) indicating the nature of the fault.

Changing transmission speed:
- Changes the transmission speed for diagnostic information from the DLC.

Diagnosis in older models

Chassis Number Table:

In older models (1992-93), with chassis numbers as shown in the table, a control module with built-in diagnostic function can be used as a 'special tool' for reading off DTCs via the DLC. The control module part numbers are 913 0197-8 or 912 8853-0.

- Replace the existing control module with the unit with the built-in diagnostic function.
- Drive the car at over 4 miles/h (6 km/h). The control module will record any faults and post DTCs. These can then be read out via the DLC in DTM 1.

With pre-92 models (1989-91), the new control module cannot be used for fault-tracing or diagnosis, as the DLC is not wired up.