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Toyota Prius Intermittent Master Warning Light Issue: SOLVED

I recently came into an issue with Prius where the master warning light would come on intermittently. Here is what caused the issue and how it was solved quickly.

I am one of those Prius repair guys that have to find a solution to every problem. Most of the issues that I have encountered with the fuel saver have been relatively easy to repair.

I recently came across a Gen 2 Prius that threw me for a loop. It would not store trouble codes, but it would intermittently set the master warning light and say "problem." I had to get to the bottom of it, and here is what I did to solve the problem.

Intermittent Master Warning Light: Solved
The master warning light can come on for a bunch of reasons. Usually, though, it comes on and stays on. So for the light to come on and off randomly.

I observed the issue for several days, with a scan tool hooked up. There were no codes, but one thing tipped me off that led me to fix the problem in just a few minutes.

When the master warning light would come on, the display screen would say issue. Some of the time, though, the oil pressure warning light would be present. I figured this was normal since the engine shut off whenever the master warning light was triggered, no engine running, no oil pressure, right?


Suspecting there was a root cause, I began digging around. After being in this industry for 15 years, I have learned a thing or two about checking the basics. I started with the most obvious stuff under the hood.

I found the engine oil was low and added a quart as any good tech would. I checked the coolant level on both sides, normal. Transmission fluid, normal, and everything else I checked was fine. I was stumped at this point and hungry, so I went for a drive to get lunch.

Can you guess what happened next? I went to lunch with no problems. No master warning light, no "problem," and no intermittent oil pressure light.

The culprit was nothing more than a low oil level. I reminded my client that checking the oil level every time they fill up on their high mileage Prius will save them from an even more expensive repair bill.

So if you are experiencing this issue, do yourself a favor and check that engine oil level before spending time and money on something super simple.

That is all for today. I look forward to seeing you in the following article. Camry hybrid owners are having brake pump failures.

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Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporters.

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Thank you for reminding me! BTW, is it just me? They(shops) tend to overfill engine oil? I need to extract some from my Prius. lol
What about the dash lights on my 2007 Prius? I ended up putting a jacknife battery disconnect at the battery so I could reset the display lights.