This is some info for you to start checking out.
Fault Code Description
DME detects a value from the engine oil temperature sensor that is too low.
The engine oil temperature sensor gives a very low value that is not plausible any more. (below -39°C).
Fault Code Conditions
Service Plan
Check wiring, wiring harness and plug connector to engine oil temperature sensor.
Check wiring harness plug connector to DME
Check engine oil temperature sensor.
Service Notes
If this fault occurs at the same time as the fault "21F761 engine oil level too low", it is likely that there is no plug connection to the sensor.
After rectifying the fault, reset the mixture preparation adaption values.