I’m trying to diagnose a p0125 code on my 99 corolla. Toyota forums seem to say Toyota didn’t follow standards on this code and it is likely also the O2 sensor, can anyone confirm if this is the case?
I’m getting no other codes, and it will run for about 30 minutes before triggering again. Last time it triggered I saw exhaust smoke on the way home, which went away as soon as I reset the code. after clearing the code the exhaust while clear does seem to be rich smelling. Engine seems to run fine, I’m not noticing any performance issues, not signs of dipping oil/coolant amounts. coolant gauge is operating and hitting the halfway point normally.
I can’t think of anything else but the O2 sensor but I expected rougher performance and don’t really want to spend $125 on a part if I don’t have to.
This person had same issue with sensors and their posts to themselves suggest loose wire https://www.toyotanation.com/threads/o2-sensor-issue-code-p0125.322160/
Do you have and obd scanner? Maybe you could look at the o2 sensor live data to rule it out or not. The running rich seems in line with the open loop fuel management. Maybe it’s something electrical like thermostat or temp sensors. You can test the sensors with a multimeter I think. Here’s what somebody said about testing the thermostat:
Feel the upper radiator hose after the engine has warmed up and determine if it is very hot or not. If it feels relatively cool, the thermostat is most likely the cause.
You can also use the obd to see what temp the radiator fluid is getting to.
Good luck!
I would need a better scanner unfortunately, relooking at the manual mine will only say if a device is reporting. O2 is listing as “not ready” but there is nothing for coolant. I’ll check the connection on the O2 sensor and clean the housing this am and drive for a bit and feel the radiator hose and see what I can find.
What did the code reader said beside the code? From my experience, bad o2 sensor doesn’t always lead to performance issue, and usually it will just bad fuel consumption. Maybe get a used one and see if it fixed the issue
It’s a very basic code reader and only had stats listed as “ready” or “not ready.” the O2 sensor heater monitor (device says HO2S) says ready but the O2 sensor says “not ready.” I’ll see if the coolant seems to be heating up this am and try reseating the cable for the O2 sensor and if the radiator hoses heat up probably focus on the O2 sensor first if the light comes back on. Worst case I get an actually decent obd2 scanner!
