Car model: 2012 Audi A6L C7
Engine: CLX engine
Transmission: 0AW automatic transmission
Mileage: 50,000 km
Trouble syndrome: Oil warning light is on
Preliminary diagnoses: I use VAS 5054A to troubleshoot the cars ECU and got a fault code P164D, which indicates to Oil Pressure Switch for reduced Oil Pressure: Malfunction. I erased the fault code with the VW diagnostic tool and then test the cars oil pressure, which is 60kPa at idle, obviously far less than the normal 120kPa pressure. Then I search for the reason of less oil pressure based on the oil pump working principle, and find out a loosen pressure-limiting valve as shown below.
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Preliminary analysis: I ask the driver if he had taken the car to maintenance recently, and he told me that the oil filter in the car was replaced recently. Hence, I am almost sure that the light comes up because the oil line was blocked by the badly installed pressure-limiting valve.
Solution: I remove the pressure-limiting valve and reinstall it immediately, and the oil warning light then goes out soon.