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2007 Toyota Prius Gone Wrong

I bought a 2007 Toyota Prius brand new from a Toyota dealership (which I will refer to as Toyota Dealership A). I have had the car serviced religiously every 5,000 miles at Toyota dealership A.

I now have 102,000 miles on it. When the Prius had 93,000 miles, the car began losing oil profusely. I was putting in about a quart every 500 miles. The acceleration began to decline. The acceleration problem was most evident going uphill. I live in the Colorado Rockies at 8,200 feet, and I work at 5,400 feet. I drive up and down the mountain at least 6 days a week.

I took it into Toyota Dealership A at 93,000 miles because of these problems. They could not find an oil leak, did not have an answer for the oil loss, and they told me the acceleration was fine. I inquired about the problems the next two times I took the vehicle in for regularly scheduled maintenances (at 95,000 miles and 100,000 miles). The only explanation they gave me was that cars with higher milage go through oil faster.

The oil check light came on around 101,000 miles. I checked the oil and it was very low, so I filled it completely. The oil check light did not turn off, and I drove the car home up the mountain. At one particularly steep section of the mountain, the car dropped to 25 mph. This is as low as it has ever dropped. (I used to be able to drive the car at 50 mph in this section of the mountain).

Tired of hearing that there was nothing wrong with my vehicle, I quickly took it to an independent mechanic. Within a half an hour after bringing it in, they told me their concern about the engine not shutting off while in park (it should only be the electric hybrid engine running). They did a leak-down test and told me they found a 40% carbon leak in the 4th cylinder, and they replaced my spark plugs. They even gave me the old spark plugs for evidence. They told me that I was looking at $3,000-$8,000 repair, thinking I may need a new engine or a new hybrid motor. They told me to contact Toyota Corporate because this was not ethically right, as I bought the car brand new and have only taken it to Toyota dealerships for maintenance.

I called Toyota Corporate and I have a case number. Of course, Toyota needs to inspect the vehicle with their own eyes before taking the word of an independent mechanic. I decided to have the vehicle inspected by a different Toyota dealership than Toyota Dealership A, where I bought it and have had it serviced (I will refer to the different Toyota dealership as Toyota Dealership B). Toyota Dealership B told me there was nothing wrong with the hybrid component. They noticed that the oil was black, and that I needed a new 12 volt battey. However, they could not get the engine check light code because the independent mechanic erased it. The next step was to replace the 12 volt battery and do a compression test.

Toyota Corporate will not tell me what they may or may not cover (or partially cover) in costs once they determine what is wrong with the vehicle. My vehicle is now out of warranty, but at 93,000 miles, when I originally took it in for these problems, the hybrid system was still under warranty (up until 100,000 miles). However, Toyota Dealership B told me nothing is wrong with the Hybrid component.

I was able to get a free compression test out of Toyota Dealership A. The test turned out just fine. However, the engine check light came back on later that day.

I took the vehicle back to Toyota Dealership B and had the 12 volt battery replaced. They told me the engine check light code was for the 12 volt battery. They also changed the oil to do an oil consumption test (I am to return it after driving 500 miles). That night, I drove the car home up the mountain. Though I knew the 12 volt battery was for starting the vehicle and not running it, I was still curious to see what the 12 volt battery would do to the acceleration. The vehicle again dropped to 25 mph during the steep section of the mountain, and the engine check light came back on. I called Toyota Dealership B. We agreed to bring the car back in after 500 miles.

I have not been driving my car up and down the mountain because I don’t want to ruin my engine. I leave it down the mountain and drive it around town for work. I am now at 500 miles, but the oil looks okay, probably because I have not been driving the car up the mountain.

I could have Toyota look at my car for the oil consumption test, but I doubt they will be able to determine anything because the oil looks fine because I have not been driving up the mountain. Perhaps I could begin the oil consumption test again, and this time I will drive it up and down the mountain for 500 miles. However, I am apprehensive of doing this for fear of ruining my engine. I have called and left a voicemail for Toyota to ask about this, but I will not hear back until next week.

I don’t know what to do. In order for Toyota to determine what is wrong, I have to continue to shell out money to have them look at it. Once they determine what is wrong, I don’t know if Toyota Corporate will cover any costs… I doubt it.

If I sell the vehicle privately, it is required by law that I take care of the engine check light so it can pass emissions. Now I am back to paying Toyota (or someone) to determine what is wrong. If I trade in the vehicle at a dealership, I have to trade it for a car of equal or lesser value because I have no more money. Therefore, after an extensive search of various dealership (not just Toyota), I am looking at getting a vehicle at the same milage or more, and additionally, it will be about 5 years older than my Prius. This feels like a gamble. What will eventually go wrong with that vehicle?

I bought a Prius repair manual, and I am thinking about replacing the valves myself.

This doesn’t seem fair, as I bought the vehicle brand new, have never been in an accident, and have only had it serviced at Toyota dealerships (except for this last inspection by the independent mechanic). Perhaps the Prius is not meant to drive up mountains at this altitude. Suggestions?


I believe your cars powertrain warranty (engine/transmission) is 5 years/60,000 miles. Hybrid related componants; HV battery, hybrid control module, inverter and converter are covered for 8 years/100,000 miles. Your warranty booklet should have the details on this.

If your able to demonstrate the oil consumption problem I think they are going to offer you a new engine at your expense. Your warranty has expired.

It is difficult to guess what is going on with your engine, knowing the fault code would be a good start. If you are adding 10 quarts of oil between oil changes there must be a ring problem and alot of carbon in the combustion chambers. This will cause detonation under load and the ECU will retard the timing resulting in some power loss. Failed rings will cause alot of blow-by while climbing a grade, someone should have a look at the breather hose to check for exessive blow-by.

You might elaborate on this compression test a bit by providing numbers and whether it was a proper test or not; meaning both dry and wet tests, leakdown test, etc.
It’s kind of surprising sometimes how many shops state that bad numbers are actually good ones.

It could be that the oil change regimen is behind this. Changing the oil every 5k miles may simply not be often enough no matter what the factory and owners manual may state. Driving habits and environmental conditions play a huge part in whether that interval needs to be shortened or not.

You state the oil was black and that’s a sign that it needs to be changed more often. Aged oil will create sludging and oil coking (burnt oil basically) problems and this often manifests itself in the piston rings by causing those rings to seize in the ring lands. That in turn causes oil consumption problems.
Hope that helps anyway.

Your Pruis might be underpowered for your driving patterns. Going up a long steep mountain means the gas motor and electric motor have to work properly in combo. If the hybrid battery is in a low charge state that also takes power from the gas motor to charge the batteries and run the car up the mountain. A lot of work for a relatively small gas engine. Highway drivng isn’t really the forte of a hybrid, and highway driving uphill is even worse, then add the power loss from a gas engine in high altitudes.

I think your gas engine is tired after all the years and miles of tough use. I’d suggest you sell the Prius and buy a conventional car. The Masda 3 SkyActive might be excellent since it has a turbp charger to help develop more power in thinner air. A TDI Jetta diesel might also work good for you.

I think the Pruis is just the wrong car for your type of driving. It is just plain worn out.

A couple of things come to mind to me. First, the drive battery has lost much of its capacity. It may test good by their standards for years to come, but it may have lost half or more of its capacity by now. That means that halfway up the mountain, the battery is completely discharged and now that little motor is your only power. The motor is not only trying to move the car, but charge the battery as well.

Second is the oil leak. I’m not sure, but I think in 2007, they were still using the 1.5 liter engine. If so, I would suspect the front main seal and/or the oil pump. Another source of a leak of that magnitude would be the oil pressure switch, and since your oil light is coming on, that makes it even more suspect. I am surprised that the dealer didn’t catch this though.

If this is the 1.5 liter engine, the oil pressure sending unit might be hidden behind the AC compressor though. If it is the sending unit, its a cheap fix.

This “40% carbon leak” on the #4 cylinder bothers me. I’m pretty sure that is not what the mechanic actually said because it makes no since, but if a leak down test indicates the #4 is leaking down 40% faster than the others and that spark plug has a carbon build up on it, then I’d be concerned about the rings on that cylinder.

That in turn causes me to be suspicious of Dealer A. I’m not going to accuse the dealer of any wrong doing as there is no proof, but there have been dealers, and other mechanics, that somehow “forget” to do the oil change you pay for on occasion, so your oil gets sludged up when it shouldn’t. You have to check your oil dipstick every time you get your oil changed to make sure it was actually done.

Since you have not been doing that, then do not make any accusations or you could face slander charges. I am not accusing the dealer of this, but I have caught a dealer doing this to my mother once. They never did it to her again. She got special treatment from them after that.

BTW, because the engine is not shutting down while in park tells me that the drive battery is discharged below its lower limit and needs the engine to run for a little. You didn’t say, but I’ll guess that your gas mileage isn’t what it used to be either. That’s another indicator of a reduced capacity battery. BTW, Toyota considers 5 years to be the normal battery life.

Thanks for all of your comments… very helpful in my decision to trade in my Prius.
My Toyota Dealer Mechanic advised me to unplug the battery and then plugging it back in before trading it in to a dealership. He said that unplugging and re-plugging the battery would make the engine check light turn off temporarily. I did this (with the guidance of the Chilton Repair Manual, and now the when I turn the Prius on, not only does the engine check light not go off, but ALL of the warning lights come on, and I cannot put the car in drive! I was planning on trading it in tomorrow morning, and now I can’t even drive my car! What should I do!?