Self-diagnosis General The EDC system continuously checks itself. It does this by running a signal-range check. During this check, all signals are scanned for presence and plausibility within a certain time frame (determined by the software). The control unit itself is also constantly checked the whole time the program is running. The first check is always carried out when the ignition is turned on. Any faults occurring during operation are stored for the purpose of subsequent diagnosis. A maximum of 5 faults can be stored simultaneously in the fault memory. The faults are stored in the order in which they occurred. If more than 5 faults occur, the least significant fault is deleted.
Fault storage includes D allocation of fault priority, D identification of the type of fault, D recording of fault frequency. Sporadic faults are recorded by a frequency counter the first time they occur. This means that a certain fre- quency number is set which is decremented by one during every start procedure. If the fault no longer oc- curs, it is deleted when the counter reaches zero. To report the fault, the diagnostic lamp either comes on permanently or remains off, depending on the sig- nificance of the fault. If several faults are stored, the steady light has priority over OFF . Only faults currently present are indicated.
Faults which are stored but which are not currently present are not indicated. There are two fault memories: D Fault memory for diagnosis via ISO interface. This memory can be read out and cleared with MAN-Cats D Fault memory for diagnosis via flash code. The flash code memory can be read out and cleared with the aid of the diagnosis button. Faults are always entered in both fault memories simultaneously and can be read out even after the ignition has been switched off and back on again. Indicator lamp check: The EDC indicator lamp lights as a lamp test for approximately 2 seconds after the ignition is switched on. 20