Hello everyone! My name is Scott and I'm new here. I have a 2012 S60 T5 with mileage of 120k. Recently the AC fan was not working, so I got to the dealer to have it checked. They said that the most possible reason was that I need to replace the blower motor resistor. After comfirming that it's an plug-in device, I decided to do it myself.
Before start, I disconnected the battery according to a video demo of changing blower motor. Unfortunately, I made a mistake and detached the positive terminal only and unplug the old resistor(without plugging in the new one since it's a hard work). After reconnectting the battery and try to reststart the engine, it took a while to run the test(because I can see the petrol gauge on the left dashboard screen was empty at first). Then the "check engine" light blinked serveral times and the engine oil pressure waring light kept on. The engine won't start.
I tried to detach the negative terminal and plugged the old resistor back. But the same problem occured again.
I checked the engine oil level and it was above the first lower"xx' on the meter. Since there was no warning on oil level yesterday. I speculate that it might be the rebooting of system that lead to the problem( or detach and reconnect the positive terminal damage the oil level sensor ?).

Does anyone have any ideas about this problem?
Thanks a lot!

P.s:
The car was parked on a mild slope. Possibly due to this?

 

did the engine start or only crank over? If your engine doesn't get to idle the oil light will stay on as the pump isn't going fast enough to build pressure. Otherwise, I'd check fuses etc for starters. You can try disconnecting the battery again, wait 30 minutes then reconnect to see if the car starts normally.

 

The engine didn't crank—— I could hear almost nothing when pushing the start button.
Does that mean it's the starter's problem or battery drain?
Thank you for your reply~