Hey folks, I drive a 2012 Mazda 3 hatchback (2.0L automatic) and recently ran into an issue I could use some help with. While driving on the highway, the car jerked hard, and the AT light came on. The check engine light has been on for a while now. I scanned it and only got one permanent code: 🔧 P0138 – O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)(This is the downstream oxygen sensor, after the catalytic converter.) What’s strange is that the scanner didn’t detect any transmission-related codes, even though the AT light came on and I’m now feeling rougher shifts. Also, just to note — I had the transmission fluid changed about 8 months ago during routine maintenance. Questions: Could a faulty downstream O2 sensor cause the AT light or impact shifting? Is this maybe a wiring/grounding issue affecting both the O2 sensor and TCM? Anyone had a similar issue with no trans codes but shifting problems? Is it safe to continue driving like this temporarily? Thanks in advance

 

Welcome aboard.

This may be a statement by Captain Obvious, with a "jerk while driving" (chuckled at that when you think about it) feeling in the vehicle and now rough shifting, sounds like something physical / mechanical indeed has changed and proceeding with caution is in order. Your details indicate ATF changed 8 months ago. By who? Dealer? Self? Independent mechanic? What fluid was used? A fluid which is too generic may be incompatible and actually cause damage. I've seen the small plastic Mazda ATF dipstick break and fall down the dip tube into the tran. The strainer/filter may catch it, maybe it didn't.

No solution here, I'm sure those will come from members with more experience. Just an encouragement to proceed with caution. Does sound like damage has occurred.