Troubleshooting P0125 (1 Viewer)

[napir]

Driving myself crazy with this one, as it's causing me to get a whopping 8 MPG. Consistent P0125 code with intermittent P0130 and P0133. FSM points to a bad O2 sensor, wiring to the O2 sensor, or bad ECU.

Replaced sensor with Denso, no change. When I run my scanner, I'm not picking up any voltage nor fuel trim whatsoever from Bank 1 Sensor 1, so I'm thinking it's the wiring to/from the sensor. FSM doesn't really help me with which wires should read what.

So, a few issues I'm running down and looking for help with:

1. 4 wires to the front sensor, please someone confirm what they should be reading

• Grey - Heater wire from ECU, instructs sensor to warm up? 12V?
• Yellow/Red - Heater wire from EFI relay, provides power to sensor, 12V
• Blue - Sensor wire to ECU, what should this read when running? Where does it run between the sensor and ECU so I can check for fraying? I lose it over the tranny and haven't yet torn into the harness cuz I'd prefer to let sleeping dogs lie...
• Brown/Black - Ground

2. Can anyone confirm the Denso sensor connector pinout? I had to splice in a replacement pigtail to replace a dried-out harness-side connector and I think I got them correct but want to confirm.

• Denso - OEM
• Black - Grey
• Black - Yellow/Red
• Blue - Blue
• White - Brown/Black

Appreciate any help!

 

[Fj80oregon]

Check the resources section for a free electrical FSM it has every system covered in detail. Also you should provide your year make and model for correct responses.

 

[napir]

Check the resources section for a free electrical FSM it has every system covered in detail. Also you should provide your year make and model for correct responses.

Thanks, I've pored over the FSM and EWD trying to figure out the wiring run, and what the readings should be. They also don't address the Denso but I know it's a popular replacement. Vehicle details are in my signature.