Cylinder 1 misfire and catalytic converter issue

[Lu Xun]

Hello everyone, I own a 2009 Toyota Yaris sedan which currently has 37,667 miles. Last night, the check engine light came on so I took it to a local mechanic who diagnosed the errors as P0301 and P0420 (autozone scanner gave me these errors too). He claimed that the cylinder 1 misfire was caused by a damaged coil and that my catalytic converter needed to be replaced. He also claimed that my transmission fluid needed to be flushed because the color was a dark tint and not red. However, the Toyota dealership told me that the transmission fluid should be good for 100,000 miles. Is that true?

As far as the cylinder misfire is concerned, I was momentarily unable to back out last night out of a driveway (nothing happened when I stepped on the gas pedal) so that is the only possible physical symptom that I have noticed. I believe the check engine light came on right after that.

Have any of you had experience with these issues and figured out a solution? Is there any way I can possible resolve these problems myself b/c I really don't want to spend more money at the dealership if I can fix this myself? I'm ashamed to say that I haven't done much maintenance on the car besides replacing the motor oil. Speaking of which, I haven't replaced it in quite some time (at least 6-7 months?) so I'm not sure if that may be a factor? Any guidance on what I should I do would be appreciated. Thanks.

[CTScott]

You may have gotten some bad gas that caused both errors. If the car feels like it is running fine, I would reset the codes, run the tank to empty, fill up with some good quality gas and watch to see if the codes come back.

As for the tranny fluid, Toyota does spec it for "lifetime", but if it has been driven hard it will need it to be replaced sooner (and it doesn't hurt to replace it sooner).

[Lu Xun]

As for the tranny fluid, Toyota does spec it for "lifetime", but if it has been driven hard it will need it to be replaced sooner (and it doesn't hurt to replace it sooner).

Is there a guide online that shows how to replace it? I can't locate the fluid container or find any diagrams that show where the transmission fluid is. Thanks for the help btw.

[CTScott]

Originally Posted by Lu Xun

Is there a guide online that shows how to replace it? I can't locate the fluid container or find any diagrams that show where the transmission fluid is. Thanks for the help btw.

If you do some searching on here there are a couple of threads with instructions on how to do so.