Possible causes

– Faulty Low Speed Radiator Fan Relay
– Low Speed Radiator Fan Relay harness is open or shorted
– Low Speed Radiator Fan Relay circuit poor electrical connection
– Faulty Electric Fan
– Faulty Engine Control Module (ECM)

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Radiator fan inoperative
– Possible engine overheating

P0691 BMW Description

The Engine Control Module (ECM) detected a low fan 1 control circuit