Annoying check engine light & minor problem won't pass emissions test

So I’ve been dealing with a continuous check engine light on my car for over 2 years with several hypothesis from different shops. The one symptom my car has is that from a stop or slow speed it sometimes hesitates to actually move when giving it gas. Then it will suddenly kick in and all is fine. This all started after having an O2 sensor replaced when my check engine light came on once - at that time there were absolutely no symptoms, no hesitation. Then the hesitation began, but the shop said it had nothing to do with the new O2 sensor and they couldn’t find anything wrong with the car. Shop #2 said I needed a new catalytic converter. I decided to get another opinion and went to shop #3. Shop #3 said it definitely was NOT the catalytic converter, but probably an O2 sensor…but I that I have 7 O2 sensors and since nothing was showing up on their diagnostic tests there was no way to know which one. To replace all 7 would be around $750. The manager said he’d feel perfectly comfortable driving my car to California and back and that if I didn’t mind the symptoms it wouldn’t hurt to go without the repair…although I might lose a little gas mileage if the O2 wasn’t registering properly. So I’ve driven another two years on the car with no problems except for the occassional annoying hesitation. But NOW it’s time for an emissions test and I confirmed by calling the 800# that the car simply will not pass the emissions test if the check engine light is on for any reason. And when I’ve had the mechanic manually turn of the check engine light, it comes back on usually the same day, sometimes almost immediately, so I don’t think I can just get it turned off to take the test. Any suggestions? Is it indeed an O2 sensor? Should I bite the bullet and pay for the repair? Since the shop isn’t certain, my fear is I’ll pay $750 just to keep having the same problem. Could it be something else?? Why does the stupid emissions test have to be based on such a silly thing that probably doesn’t effect my emissions whatsoever. I mean, I’m all for reducing green house gases, but c’mon, this is silly. Any help would be greatly appreciated! My test is due on January 12th.



You have to tell us what the code was- for example p0112 etc.

Your vehicle doesn’t have seven O2 sensors. There’s only two. One before the catalytic converter and one after the catalytic converter. And the only one that can have an effect on engine performance is the O2 sensor before the catalytic converter. So if they’re saying there’s a problem with an O2 sensor, the one before the catalytic converter has to be it.

But if you could provide the actual diagnostic code(s) that’s stored in the computer it would narrow it down. Parts stores like Auto Zone will pull codes for free.


Any chance you misunderstood what they said and took the word “several” to mean “seven”.
If your car had 7 O2 sensors, which it does not, you would not likely be getting off the hook for a total replacement cost of 750 dollars.

Other than agreeing that you should get a parts house to scan the car and post any codes, one issue with something like this is the fact this has gone on for several years. What may have originally been a minor 5 minute fix (vacuum leak for example) may have snowballed and created a number of problems.

And emissions can be affected whether any driveability problem is noticed or not.

It is possible that the first mechanic used an aftermarket O2 sensor that is not an exact match for the application, or the replacement sensor might actually be defective. I would start with that.

If the code pulled is a P0420, which seems to be common on Corolla’s, then I wish you the best of luck. The first thing that mechanics jump on for this code is the catalytic converter, and most of the time it doesn’t fix it. More often, the second O2 sensor, the one behind the cat will solve it, but not always.

My daughters Corolla has this problem, and so far nothing has worked. A co worker had this with her 09 Corolla. It took many visits to the dealer to get it fixed, but the dealer will not say what they did to fix it and did not supply a repair receipt for that last visit.

A good tech can display the signal traces from both O2 sensors simultaneously on an oscilloscope and see exactly what’s going on, even if it turns out that the wrong O2 sensor was used…the signal will trace out of spec. Let your fingers do the walking through the yellow pages and seek out a shop that can perform this level of diagnosis.

As to the second question, why does the emissions teat have to be based on such a silly thing, nobody can answer that one. We’ve discussed this at length ourselves, and the only answer is that it’s all politics. And revenue.

Sounds to me like they are giving you the run around. You need to find a shop with a good reputation. A corolla does not have seven 02 sensors. You should get the code from autozone first before going into a shop. Also research the code you receive along with “Technical Service Bulletin” your code will come in the form of the letter P followed by four numbers (P1234) So when googling this try many different ways such as “Toyota Corolla P1234” or “Toyota Corolla P1234 technical service bulletin.” This just might be a common problem with this car. Due to the popularity of this model, I own one myself, there has to be others with the same problem on a forum somewhere.

It really would help us if you had included what year the Corolla is, how many miles are on it, and which engine it has. Manual or Automatic might sometimes make a difference.

That check engine light code would be very helpful also.

Regardless of what year Corolla it is, it most likely only has 2 O2 sensors.
They typically cost between $50 and $150 each, and you should only need to pay 1 hours worth of labor to install them. So, tops, you should be paying about $450 for both.

Hesitations, however, can be caused by so many different things, I can’t list them all.
Here’s my short list, however:

MAF Sensor.
Dirty Throttle body sticking.
Faulty EGR, or controlling solenoid.
Faulty spark plugs or ignition wires (when was the last time you had these replaced?)
Faulty distributor cap or rotor, or ignition coil stick.