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08 Toyota Sienna: fog..the Check engine, VSC and Trac Off lights came

Customer Question
I have an '08 Toyota...
I have an '08 Toyota Sienna with 90,000 miles on it. During a recent long trip (much of it in rain and fog/mist), the Check engine, VSC and Trac Off lights came on. Performace didn't seem affected. Following a stop for lunch, the lights did not come on with restart and we drove several miles before they came on again. The dealer's mechanic said that one of two sensors -- as determined by putting the vehicle on a tester -- was usually the culprit behind this and that they would replace the most likely first -- and then the 2nd -- if the situation wasn't cleared. He also said that my gas mileage would be affected. Here are my questions: 1)This appears to be an intermittent situation; shouldn't a visual check for loose wires, etc., be done first? 2) How would a bad sensor affect gas mileaage? I drove over 600 miles with the lights on most of the time and got 27.3 MPG! Although I have an extended warranty agreement, preplacing these two sensors would cost me over $600! What's going on?
Submitted: 6 years ago.Category: Toyota
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Answered in 5 minutes by:
8/14/2011
Toyota Mechanic: ToyoPro, ASE Master Certified replied 6 years ago
ToyoPro
ToyoPro, ASE Master Certified
Category: Toyota
Satisfied Customers: 1,303
Experience: Master Technician, 17yrs Automotive Industry
Verified

ToyoPro : Hello and Welcome to JustAnswer. I am reviewing your question and will be back with you in just a second.
ToyoPro : Do you know what codes were stored?
Customer:

no, guess I should have asked

Customer:

actually that is another gripe -- I should have been offered a sheet that showed the codes and a few details on the sensors affected.

Customer:

dont see the answer my email says i should have here

Customer:

are you there?

ToyoPro :

It is common for several sensors to fail on that model. We see a good number of ignition coils and oxygen sensors fail. Most times when a sensor starts to fail it will give a reading out of spec. When that happens the lights will come on. When that happens you may not notice a drop in fuel milage until complete failure. I would hope to think that they did perform a visual check of the affected parts while performing diagnosis.

Customer:

I am disappointed that "it could be one of two sensors" -- this means that if I/they guess wrong on the first replacement, I have wasted a lot of money on essentially a diagnostic experiment. I don't think this is fair

ToyoPro :

Is your check engine light still on?

Customer:

it was this a.m.

Customer:

and has been on since got back from trip -- only for for period of hour or so on the long trip. Came back on after a rest area stop

Customer:

only off for a short period, that should be

ToyoPro :

Most auto part stores will check it for free(like Autozone). If you could get them to check it for codes and post them here I will be glad to take a look at what it could be.

Customer:

ok, I will do that. My sense is that an ignition coil is a go-no go device (like an electric switch) -- it either works or you are dead, so no such thing as gradual decline affecting gase mileage. What device/function does oxygen sensor check. I still maintain that a failed sensor by itself has no bearing on gas mileage -- but concede that maybe the system or device it monitors might.

ToyoPro : A oxygen sensor reads the amount of unburnt fuel in the exhaust and works with the air fuel ratio sensor to adjust the amount of fuel to inject into the engine.
Customer:

i see; -- so it is not merely a sensor -- it controls a device that adjusts the air/fuel ratio. Now tell me, what does the ignition coil or the gar/fuel adjustment have to do with the Trac system and/or the Vehicle Stability Control system?

Customer:

thats "air/fuel" adjustment

ToyoPro : Any time the check engine light comes on the trac and or vsc lights will come on as well.
Customer:

well, guess there is no sense in looking for an answer to this illogic....lol. thanks for your help. I will pay you for your time, but don't want to open a justanswer account. How do I do this?

ToyoPro : Just click accept for this answer and then go to My Account at the top of your screen if you want to cancel your account.
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Toyota Mechanic: ToyoPro, ASE Master Certified replied 6 years ago
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ToyoPro
ToyoPro, ASE Master Certified
Category: Toyota
Satisfied Customers: 1,303
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Experience: Master Technician, 17yrs Automotive Industry

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