I have a 2009 Prius with 179k miles. I was driving home from work and my Malfunction Indicator Lamp warning light came on. Once I made it home, I checked all the fluids and found the oil level to be very low. I added about a quart and a half. The next morning, I started the car and the warning light was still on. After a five minute drive, I dropped my son off at school and turned my Prius back on again, the warning light went off. I still wanted to run diagnostics to see if any error codes came up. One came up and it was P1121- Coolant Flow Control Valve Position Sensor Circuit Stuck. However, my warning light has continued to stay off. Can I still drive my Prius until the warning light potentially comes back on or should I avoid driving my car until I have a mechanic evaluate it? I appreciate any feedback, thanks in advance.
There are 2 potential lights that will come on in the situation you described. With low engine oil, the warning light that comes on would be the "big red triangle". Letting you know something is wrong. The P1121 Coolant valve is an emission related component that will light up the "check engine" light. They should not be the same warning light that come on. Also the Prius requires a more high end specific code reader to access all the codes. You may not have the proper scanner to read all the codes.
Being 1.5 quarts low on oil won't turn on any lights or set any codes. The malfunction indicator light (MIL) is also called the check engine light ((CEL) because, you know, it has a picture of an engine with the word "check" under it–LOL) will come on for a P1121 and can be intermittent so will switch the light on and off until it stops being intermittent. As bisco said, it needs fixing, but is not urgent and will not cause any damage or problems if you continue to drive your car until you get it fixed.
