I think that some fault codes can appear as a by-product of some other faults. For instance you may truly have a bad crank sensor, which causes poor ignition, which causes incomplete combustion, which causes a rich reading at the O2 sensor, which causes the fuel trim fault code .......(you see where I'm going).

For instance I was once troubleshooting an occasional no-start problem on the mother-in-law's 89 740. The only fault code I was getting was the fuel trim too rich or too lean code. The real problem - bad Radio Suppression Relay, (which causes the injectors to not open properly).

Take Mark's advice and replace the crank sensor and then see where you stand.