I have a 2017 Equinox with a 2.4 liter engine. I've been having issues with the check engine light coming on for several days, going off for a few days and back to on again. The error codes are P0138 and P2271. I replaced the downstream O2 sensor with a Bosch sensor that was supposedly a suitable replacement (seems like I should have went OEM). This did not fix the issue. I'm tempted to buy an OEM sensor to replace the Bosch one, but I wanted to do my due diligence before buying another sensor. I unplugged the downstream sensor and tested the heater circuit voltage and got 9.8 volts. Is it supposed to be 12 V? Other bits of info: 1) I measured resistance from the heater circuit ground to battery ground to be 3.3 kohms. 2) The old sensor I removed measures 50 ohms from the black sensor wire to the heater circuit (I also get about 6 ohms across the heater circuit). I don't think the new Bosch sensor measures any resistance from the black sensor wire to the heater circuit. 3) After 15 minutes of the engine running and the O2 sensor unplugged, the Bosch sensor reads back about 0.6 volts.