First Check Engine light! P2243

:
2009 Mazda5 GT
After 125,000 miles the check engine light finally came on. It had P2243 - O2 Sensor Reference Voltage Circuit Open Bank 1 Sensor 1.

So the PCM wasn't getting a voltage signal from the front (upstream) O2 sensor and was running in open loop. Before spending close to $200 on a new sensor I disconnected and reconnected it to make sure it was tight. I cleared the code and let it idle for a few minutes and everything was ok. No CEL, no codes, running in closed loop. Maybe the sensor connector had loosened a bit from vibration? I guess I'll just keep driving and see if the code comes back.

Hope this helps anyone in case you get a P2243.
 
Well that didn't last long. The CEL came back on and the code came back the next day. I followed the procedure to diagnose a P2243 from alldata and indeed it needs a new O2 sensor. I guess it was worth a try
 
A helpful tip someone mentioned was to try and tighten the sensor about 1/8 turn to crack the seal before removing it. Otherwise lots of penetrating oil and let it sit a while. I sheared off the threads of the old one and needed a thread chaser to clean it up
 
The new sensor is in and after a few days of driving, no check engine light. Looks like problem solved. Fortunately the old sensor came out easily, only took a few minutes to replace
 
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