Low Engine Oil Pressure Advice

A basic OBD2 scanner isn't going to tell you anything, you need a scanner that's able to read the sensors directly. That way your looking at whatever the computer is seeing. You may have a bad oil sensor, but you'll need to test it and place a manual oil gauge on it to verify accuracy. It may also be bad oil. What kind of oil are you using? Are you using a quality, full synthetic 0w20 oil?
I've had oil break-down on me, but that was 40 years ago. Was using 30 wt oil, when I did my oil change - it drained out like water @ just 5K miles on it. Switched to Castrol and never had that issue again. When I inherited my dad's truck, had low oil pressure when hot and idling. Did an oil change with Castrol oil - no more issue. Later found out it was Jiffy Lube oil, so whatever cheap stuff they're using isn't good for any engine - IMHO......

 

For Gen 3, at 180K miles, usually you'd be at the stage of the high-MPG piston rings failing and burning oil. How has the oil level been? Are you up to the one quart loss per 1000 miles yet?

 

A Gen 3 Prius only has an oil pressure switch. The oil switch is either open or closed, so a scanner will not tell you anything more than what the low oil pressure light on the dash can do. The only way to see the actual oil pressure is to add a pressure gauge or pressure transducer.

 

You don't sound 100%. Could you see a definitive top-of-oil, or it was smeared so much you're not sure. Check on level ground, and after pulling/wiping the dipstick, wait 5 minutes before reinserting for the check. The dipstick is prone to pull oil up the tube, make it difficult to discernt the true oil level. Your year will for sure have the low-tension piston rings, more prone to oil consumption, fwiw.

Ever cleaned the EGR system?

 

The low oil pressure switch is easy to change and relatively low cost. Access by removing the passenger's front wheel and an access panel in the wheel well plastic.

 

Have a real oil pressure test done, then use those results to decide whether the oil pressure warning sensor is throwing false alarms or if your engine is actually worn out.

 

You'd need to be more than 2 quarts low on oil for that to be the source of the problem.

 

Bam!!!

 

Low oil pressure light means no oil pressure which means no oil. When you say "...I wasn't super sure, but I thought it might have been low so I topped it off with a quart of oil" that sounds like a dribble of oil on the dipstick caused by the curved holder. It has to be solid but normally only on one side of the dipstick.

OR the light is actually something else which has been the case in the past.

What the egr has to do with it is beyond me.

 

most people think oil pressure warning light (imminent engine failure) is actually just the low oil warning light. We have an ongoing campaign to raise awareness about knowing how to check your dipstick but we are failing so often... :'-(

It seems more an issue in Gen2 Prius age cars right now, but gen3 is on the horizon.

 

If he "topped it off", with a quart of oil and it's now full - the car was down a quart. Otherwise it should be way over filled NOW; if oil was touching the stick to begin with! He needs someone else to verify his work or what he's seeing. A gen3 with 180K, would be burning a significant amount of oil - at least a noticeable amount.

 

Best reply describing the permanent issue.

 

User oil mismeasurement issue eh?