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Pre-2001 models tended not to have a standardised diagnostic system, although primitive pinpointing hardware did feature on many cars throughout the 1980s and 1990s. Blink code readers, indicated by a flashing LED display, were popular and the following process explains one such system and how it was used to identify a failed central locking motor before any dismantling took place.
Each port accesses an ECU: port 1 is for the central locking/ immobiliser, port 2 is the fuel system, port 3 is the ABS, port 6 is the cruise control and port 7 is for the SRS and airbag. A4
To read the fault codes indicated by the blinking LED, the user depresses the centre button a specified number of times, with a set sequence of pauses. A3
This 1993 Volvo has a diagnostic port on its nearside front suspension turret, which indicates fault codes and can provide input and read output signals. A1
With the cover removed, note the jumper wire, six ports for each ECU (one unused), an LED lamp and the push button. This unit is in good condition. A2