To my understanding, on an Audi A4, error code P1392 indicates camshaft sensor circuit. This could be a faulty sensor the camshafts are not correctly timed. 90s Audis are not very common in my country but from what I can gather
:The mark for the crankshaft gear is on the cover you have to remove in order to get at the timing belt. The sprocket you may be having trouble with is the intermediate shaft (in front of the water pump) and I don't believe that one matters at all since it doesn't drive any of the cams. The intake cams are driven by a chain off of the exhaust cam shaft so only the exhaust cam is driven directly by the timing belt.
Additionally, you may benefit from the Audi A4 Service Manual
and/or Audi A4 Cabriolet Workshop Manual
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
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