Master Warning Light truble.

I would think there would be some stored error codes.

Any chance they gave you can get a diagnostic printout that identifies any codes that occurred?

 

Check engine oil level. It must be very low.

 

It could be a bad oil sensor, if the oil is full.

 

Probably whoever did the diagnostic doesn't have a code reader that is Prius aware. If red triangle is lit, codes are definitely stored.

Sounds like you either have low oil pressure caused by a pump malfunction, bad sending unit, or possibly a ECU acting up.

Find someone who has a code reader that is for a Prius and I would bet you will find a stored code. Is there a Toyota dealer you can go to?

 

Find someone who has a code reader that is for a Prius and I would bet you will find a stored code. OR take it to a Toyota dealer.

 

It could be any number of things. Again, get someone who has a code reader that will work on a Prius.

That is why I said take it to Toyota.

Once you have the codes read, you will have an idea of what is actually wrong. It is obvious the person who is working on the car doesn't have a scanner that reads Prius codes, otherwise there would be a code showing. A red triangle (master alarm) ALWAYS produces at least one or more codes.

 

1. Do not continue to drive the Prius with the engine oil warning light on, as that will cause damage to the engine.

2. I doubt that any DTC would be logged due to low oil pressure. If any DTC were logged, the check engine light would be on. The presence of the master warning red triangle by itself does not necessarily require any DTC to be logged. For example, you can get the triangle to appear by opening the driver's door while the gear selector is in D. No DTC would be logged in that instance.

3. An overfilled transaxle ATF has nothing to do with the engine oil, but that should be addressed by removing the transaxle ATF fill plug and letting any excess come out, while the Prius is raised up in a level position. Then replace the fill plug. If the transaxle ATF is severely overfilled, that will cause damage to the axle seals at minimum.

4. Regarding the engine oil warning light, ask your shop to install an oil pressure gauge so that the engine oil pressure can be measured. This is done by removing the engine oil pressure switch located near the engine oil filter.

When the engine is warmed up, the oil pressure at idle should be at least 4.2 psi; while at 2,500 RPM, it should be at least 22 psi. Use the inspection mode to get the engine to run continuously.

5. How many miles ago was the engine oil was changed? What viscosity was used? What does the oil look like on the dipstick?

If you have any doubt about the quality of the engine oil, the oil and oil filter should be replaced now. Use a quality 5W-30 oil and a Toyota-branded filter. Check the oil pressure again with the new oil and oil filter installed.

6. I ask the OP to take a sharp photo of the "oil lamp", and post it.

 

Its very odd that it only happens while accelerating. Its probably able to meet the min oil pressure at idle but not above that. The best thing to do is like Patrick said and hook up a pressure gage to the engine to monitor oil pressure at various rpm's.

Just so you know, it is very hard to overfill the transaxle since the fill hole is at the level of fill. Presumably, any extra fluid poured in would drain out the fill hole. Additionally, you wouldn't get the low oil level light.

 

it is possible. Is it still doing it?

 

Yeah, the only real way to move forward is to hook an oil pressure gage up as Patrick stated and monitor pressure over various rpms. If you have good pressure, it is the sensor, if you don't have good pressure, its likely the pump.