Mid Road-Trip my check engine light came on, but car made it the final 5 hours and I didn't notice any changes in performance. However, would now like to fix whatever it is that's wrong.

Upon diagnostic system check, found:
Position #2 = 2-2-1 Heated Oxygen Sensor(Rich mixture/part throttle)
Position #6 = 2-1-4 RPM sensor signal absent intermittently

The 2-1-4 has registered before, is it possible that the crank position has been in need of replacement, and a resulting improper fuel burn has resulted in the Oxygen sensor getting messed up?

Were this the case, would the system switch to pre-programmed open settings, thereby explaining the fact that I haven't noticed too much difference, or would see larger problems?

1989 240DL Wagon 150,000Kms, computers already replaced

THANKS!
Steve