Control-unit-internal faults can occur on all control units for which the workshops usually have no fault remedy measures. In such cases, the control unit software or internal hardware (consisting of microprocessor, memory, I/O components, internal sensors, and similar) have to be tested.
A test of this nature is run in the self-test.
Other components are also checked. The resulting fault code entries, however, may also be attributed to other faults or problems. For this reason further information is evaluated in the test module for the control unit self-test in order to determine whether the problem really is a control unit fault.