I've checked most of the posts related to ASD and didn't found any clear path to solve the problem that I have.

ASD warning lamp came on while driving and stayed on since that time. I've tried to read the error code from the control unit, but the reader is useless because the LED is always on like the warning lamp (the # 5 pin of the test connector correspond to pin # 2 of the ASD control unit which also feed the warning lamp).

Could an external component failure be the cause or should I suspect an internal short circuit of the control unit ?

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DR
1992 300D 2.5T 351 000 km