Self-Diagnostic System: Description

NOTE: Self-diagnostics for fuel system and ignition system are covered separately in this article.

The fuel injection system and ignition system feature a built-in self-diagnostic function for fault tracing. A common diagnostic unit, located in the engine compartment behind the left strut assembly, interfaces directly with either ECU. The diagnostic unit has a push button, a Red Light-Emitting Diode (LED) and a selector (coding) cable. See Fig 1 .

Fig 1: Bosch & Rex-I Diagnostic Unit

Courtesy of VOLVO CARS OF NORTH AMERICA.

Once the selector cable has been inserted in the correct slot, depressing the button once, twice or 3 times selects from one of 3 control (fault tracing) functions. Faults stored in ECU memory are read via a system of LED flashes. All fault codes have 3 digits, each capable of ranging from 1-to-4 digits. Since all codes have 3 numbers, each code requires 3 series of flashes. For easier reading, a 2.5-second interval separates each digit of the code.

Socket No. 2 in the diagnostic unit is used for fuel system testing. Socket No. 6 is used for ignition system testing.