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@Joshua Bayada If both your O2 sensors are cycling then you are definitely in closed loop. Your tuner may have set the rear O2 sensor off in the FAA periphery settings which is known to cause P0125. The high flow thermostats open sooner (at a lower temp) in the warm up cycle, and would only cause this problem in winter by over cooling. The standard thermostat will not cause a P0125. The difference between coolant types A & B won't affect the warm up time or the operating temperature that much. When P0125 is thrown, the ECU assumes a fail safe coolant temp of 80 deg C and keeps operating correctly so it won't do any harm.
Once you get your Tactrix pull your ROM, post it up, and let us know if you need more help to check the FAA settings.
How will I know the sensors are cycling? Can I tell by the obd2 tool I have? I'll ask my tuner if he did something with the sensors. Is it normal after several months of being tuned for the car to start throwing errors? Thought it be instant being electronic lol and not take a few drives for the light to show and the P0125 code when scanned. Old high flow thermostat was alright in winter but doesn't really get cold here in winter. The Typa A coolant I have is the Penrite 10 tenths race coolant. Recommended is type B Blue, Red and green coolants for my car. I will email my Tuner just to get an idea of what he changed. I had sent the Ecu as he's in a different state to me but will also save up for a tactrix tool. Which one should I be getting in terms of Tactrix? Probably be a little while before I can buy one as they're over $300AUD
You may be able to view the O2 voltage for front and rear sensors using your OBD2 tool - depends on the tool.
If they are cycling the voltage swings between 0 and 1 V every few seconds as the ECU adjusts the amount of fuel required to hit a stochiometric AFR of 14.7.
P0125 may just now be getting thrown because the change to Penrite and stock thermostat has increased the time to reach the min temp for closed loop.
Get the Tactrix Openport 2.0 with the Mitsubishi adapter or the Evoscan 1.3U cable
You may be able to view the O2 voltage for front and rear sensors using your OBD2 tool - depends on the tool.
If they are cycling the voltage swings between 0 and 1 V every few seconds as the ECU adjusts the amount of fuel required to hit a stochiometric AFR of 14.7.
P0125 may just now be getting thrown because the change to Penrite and stock thermostat has increased the time to reach the min temp for closed loop.
Get the Tactrix Openport 2.0 with the Mitsubishi adapter or the Evoscan 1.3U cable
I'll monitor the sensor voltages when i start the car later using the ToolPro Obd2 tool I bought from work and make sure it's not changing vastly every few seconds. I am leaning towards the race coolant I put in causing it but never had an issue with a high flow thermostat before so am probably going to put the high flow thermostat in through the week when i get it, check to see how it goes for a few days with the race coolant, if it throws the error again I'll flush it out and put normal stuff back in and get one of those tactrix tools with the Mitsubishi adapter which i can get for about $350AUD and get the ROM
My tuner has emailed me back saying the rear o2 sensor has been turned off and has also faced the same problem on another car as well. I need a tactrix so i can disable the imobiliser on my spare ecu so i can atleast still get to work lol or send my spare ecu to another place I know get immobiliser disabled and when it gets back than send my current ecu back to my tuner and keep my car on the road as I need to get to work In writing about o2 sensor
i skimmed through your post and it sounds like you have a intermittent wiring problem. i work on cars for a living and have quite a bit of daig experience. for one testing for voltage at a wire does almost nothing for you. you cant properly test a circuit when there is power attached. disconnect the battery. perform a continuity test from the input of the coolant temp sensor at the ecu with the harness UNPLUGGED. back probe into the connector so as you wont damage the front part of the ecu plug that the male pin inserts into. check for ohms above 4-5 while you do a wiggle and pull on both ends of the circuit. helps if you have a min/max setting for the DMM because sometimes it will only appear for a instant and you will miss it, in this case set it for max and it will display the highest reading it finds at all times. if you find a reading while moving a certain area of the wiring then check for damage from heat or breaks in the wire. etc. then retest, then road test. hit the the freeway hit a bumpy road. i will say this. try and keep it stupid simple. if you havent seen a code for coolant temp or 02 sensor circuit as an issue so there is no reason to assume either would be a reason. you have 0.1 volts for 02 circuit which means you have a connection. in open loop the car runs off the fuel map its tuned with and there is no feedback or "talking" with the sensor. thats why you see no normal voltage readings at the 02 sensor. youll notice that when the car enters closed loop you will start seeiung voltage readings and your trim levels will start adjusting. i can only give you mediocre advice because im not able to physically be there but i can also say this. whenever i unplug my ecu, specifically the harness that has the 02 sensors in it. the fans will instantly turn on. not sure why this happens. never cared enough to figure it out but the main power wire that supplies 12v for every sensor in the MFI circuit comes through the fan relay. mine is red and yellow. turn your key on and listen for the mfi relay to click, if it doesnt click then you im almost certain that at the ecu either in the plug with the 2 02 sensor wires or the plug with the main power, ground, and sensor ground wires there is a bad connection between a pin from the ecu and the connector. ive seen this many times. the female part gets pushed up and no longer makes a tight connection. try reconnecting the connector or pushing it in further. they can appear to be plugged in but do not click. they slowly work out but will not come unplugged, check the females pins of the plug. check the face for damage. ive already replaced my whole main engine harness for this specific reason once. i very well could be wrong but its worth investigating for sure. remember testing voltage does nothing for you. that is essentially for testing a light circuit. you need to disconnect the circuit for a true resistance reading. also if you have a power probe check for good ground right at the ecu harness unplugged. these cars are super picky with this type of thing it caused me alot of grief once similair to your issue
i skimmed through your post and it sounds like you have a intermittent wiring problem. i work on cars for a living and have quite a bit of daig experience. for one testing for voltage at a wire does almost nothing for you. you cant properly test a circuit when there is power attached. disconnect the battery. perform a continuity test from the input of the coolant temp sensor at the ecu with the harness UNPLUGGED. back probe into the connector so as you wont damage the front part of the ecu plug that the male pin inserts into. check for ohms above 4-5 while you do a wiggle and pull on both ends of the circuit. helps if you have a min/max setting for the DMM because sometimes it will only appear for a instant and you will miss it, in this case set it for max and it will display the highest reading it finds at all times. if you find a reading while moving a certain area of the wiring then check for damage from heat or breaks in the wire. etc. then retest, then road test. hit the the freeway hit a bumpy road. i will say this. try and keep it stupid simple. if you havent seen a code for coolant temp or 02 sensor circuit as an issue so there is no reason to assume either would be a reason. you have 0.1 volts for 02 circuit which means you have a connection. in open loop the car runs off the fuel map its tuned with and there is no feedback or "talking" with the sensor. thats why you see no normal voltage readings at the 02 sensor. youll notice that when the car enters closed loop you will start seeiung voltage readings and your trim levels will start adjusting. i can only give you mediocre advice because im not able to physically be there but i can also say this. whenever i unplug my ecu, specifically the harness that has the 02 sensors in it. the fans will instantly turn on. not sure why this happens. never cared enough to figure it out but the main power wire that supplies 12v for every sensor in the MFI circuit comes through the fan relay. mine is red and yellow. turn your key on and listen for the mfi relay to click, if it doesnt click then you im almost certain that at the ecu either in the plug with the 2 02 sensor wires or the plug with the main power, ground, and sensor ground wires there is a bad connection between a pin from the ecu and the connector. ive seen this many times. the female part gets pushed up and no longer makes a tight connection. try reconnecting the connector or pushing it in further. they can appear to be plugged in but do not click. they slowly work out but will not come unplugged, check the females pins of the plug. check the face for damage. ive already replaced my whole main engine harness for this specific reason once. i very well could be wrong but its worth investigating for sure. remember testing voltage does nothing for you. that is essentially for testing a light circuit. you need to disconnect the circuit for a true resistance reading. also if you have a power probe check for good ground right at the ecu harness unplugged. these cars are super picky with this type of thing it caused me alot of grief once similair to your issue
my tuner disabled my rear o2 sensor which was causing it. He since disabled it a different way and is now all good. Had nothing to do with my cooling system or wiring 😅
