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02 WRX throwing P0031 cel and resistor mod not working

6K views 4 replies 3 participants last post by  DaveC03wrx 
#1 ·
I have an 02 WRX that is throwing a P0031 cel. It will do this even after putting 2.2k Ohm resistor across heater lead socket. When I short the heater leads it will throw a P0032. It will still throw a P0031 when 4 2.2K are in parallel for 550 Ohms. Anyone have this problem. I did notice my current o2 sensor has open heaters (infinite resistance).

Anyone have this problem before?

Thanks, Pete
 
#2 ·
Only thing I can suggest is to tune the car. I assume you need the resistor because you have a downpipe/no cat. What you're doing with a tune is telling the ECU not to throw a code when it sees further variance from the o2 sensor. It allows the sensor to still be used to accurately maintain A/F ratios though. A used AccessPort is what I'd recommend if you're on a budget.
 
#4 ·
If it's stock, and it's throwing that code, there's a reason, and it's likely a bad o2 sensor. That would cause the CEL even with the resistor. The resistor "mod" only changes the voltage when the temperature is colder than it should be, due to no having a cat heating up the exhaust. The resistor makes the ECU think the o2 sensor is hotter than it is, thus correcting (ish) the different reading. If you're running stock, I'd assume the o2 sensor is bad, or you have another issue where the car is running rich or lean and that's what's throwing off the sensor.
 
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