Always have control!

When checking a vehicle for a circuit fault DTC you should always check for your powers and grounds, as we have talked about in the past. This past week, I went out to a shop that was having issues with a vehicle which was constantly throwing a P0161 Bank 2 Sensor 2 Oxygen sensor heater control circuit. The shop has already verified voltage to the circuit, and replaced the Oxygen sensor 3 separate times trying to repair the vehicle. During my diagnoses I load tested the heater circuit which failed the load test, but would pass if I supplied a separate ground to the circuit. So this lead me to go to the PCM and perform a load test to the sensor pig tail (with me supplying the ground at the PCM connector) this test pasted, which then lead me to check my circuit control device which in this case was the PCM. With everything hooked up properly (but the oxygen sensor disconnected), and probed in at the PCM connector for the ground control wire for this circuit, I was receiving a bias voltage of 8v on the ground wire. I then checked the know good sensor (bank1 sensor 2) and for that system I was reading 0v as I should on this circuit. Which lead me to recommending a pcm for this concern (after checking powers and grounds to the pcm). So what did I actually do to properly diagnose this system? I checked for my proper power and grounds, but with this circuit being a more advanced circuit than normal it lead me to checking if the PCM was controlling the circuit as it should. With all that said, don’t be scared to test a circuit that is controlled by the PCM/ECM, just as long as you are not applying powers or grounds to circuits that shouldn’t have them you will have no issues.