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Discussion Starter · #1 ·
Hello all,
I’ve got an issue with my o2 sensor (s) or my pcm.
I have already replaced the b1 sensor and it did not fix the issue and that?s why I started testing everything. The vehicle is running very very rich on b1 (-25 to-30 LTFT

here are the codes
P0031 - HO2S Heater Control Circuit Low (Bank 1, Sensor 1) (SES, Current)
P0138 - 02 Circuit High Voltage (Bank 1, Sensor 2) (Pending)
P0158 - 02 Circuit High Voltage (Bank 2, Sensor 2) (Pending)

I have recently unplugged the pcm and o2 sensor harnesses and checked resistance of all wires related to the oxygen sensor system and everything checked out flawlessly with 0.0 ohms on every single wire. The grounds all check out to engine ground with 0 ohms when the key is off and 2.5 ohm when the key is on. I have tested the o2 sensors with a multimeter and they all check out as well. (8 ohms across the heater element)
After that I did key on voltage for the heater circuits and sensor wires.
B1S1 tested as follows
Red: 2.5V
Orange: 4.25V
Brown: 2.7mV
Black: 2.5ohm to engine ground with key on

Green: 2.5V
Grey: 4.25V
Violet: 2.5mV
Black: 2.5 ohm to engine ground with key on

Red: 2.5V
Yellow: 4.25V
Tan: 2.9 mV
Black: 2.5 Ohm to engine ground w key on

Green: 2.5V
Pink: 4.25V
Grey: 2.5mV
Black: 2.5 ohm to engine ground w key on

I’m thinking it needs a pcm at this point.
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