Check Engine Light Issue

[monopoly_king]

Sorry if this has already been addressed somewhere, but I'm new to the site and didn't find this in the search. Of course, I may have been using the search incorrectly. Anyway,

I have a 98 Corolla with about 175k miles on it. About 2 months ago, my check engine light came on. While it was on, my gas mileage would plummet. I went to Advance Auto Parts, and they showed that it had a code P0125. However, I found that if I would let my car warm up for about 2 minutes before driving, then the light wouldn't come on. That worked for a while, but last friday, the light came back on and is now staying on. I went and had them read the codes again, and I now have 4. They are as follows:

P0125
P0171
P0130
P0133

I've found a little on 3 of the 4 above, but nothing on how they relate to each other. With this combination, does anyone know what the root problem is? or are there multiples? Any help would be greatly appreciated. My car knowledge is limited, especially to these small "foreign" cars where everything is tightly packed under the hood. I've mainly dealt with older ford trucks.

Thank you!

[Davidzot21]

Hi, it appears that you have two issues.
1) Ensure that the cooling system is working properly and if so, replace the coolant temperature sensor for the ECU.
2) Eliminate exhaust leaks etc. that will affect the oxygen sensors abilities. Replace the oxygen sensor bank 1 sensor 1.
Not to be rude but, I strongly encourage you to purchase genuine Toyota parts as I do this for a living and see many vehicles that the owner or independent shop found the problem but, used aftermarket parts that do not meet Toyota/Lexus specifications therefore causing more issues and not solving the problems.
I hope this helps, Good luck!

[bail_w]

Use Denso o2 sensor

[monopoly_king]

Thanks to you both. I'm new to this and finding people who are this helpful is very nice. The Denso O2 sensor is the same as the original factory one?

Also, where exactly is this Bank1 Sensor1 located? Is it accessible from under the hood?

thanks again for all help

[BigTDogg (MA)]

Originally Posted by monopoly_king

Also, where exactly is this Bank1 Sensor1 located? Is it accessible from under the hood?

It's on the front pipe, part 6 in this illustration:



I think it's easier to reach from underneath, but not 100% sure on that.

[Phlingwinger]

If you remove the six (06) 12mm bolts from the heat shield over your exhaust manifold (item 4 in the picture from the earlier post), the forward O2 sensor is easily accesible from the top of the engine on the driver's side. The wiring harness is about one foot long and does not detach at the O2 sensor, so you will have to follow it to the driver's side and upwards to locate the connector, you may want to spray the bolts with some "PB Blast" or "Sili-Kroil" to help break them loose...do this when the engine is cold and several times before you actually take a wrench to the sensor mount nuts...good luck!

Phlingwinger