My car threw CEL code P0031. Before going out and buying a new A/F oxygen sensor, I figured I’d do some basic checks. I don’t have the complete factory service manual (I just have the basic maintenance and dealer setup manual) and was hoping someone here could help me out and perhaps the answers will help others. I disconnected the sensor’s connector on the top front of the engine. With the ignition key on but the engine not running, I saw ~12.0 VDC across the engine side of the harness heater wires. I then checked the resistance across the two black heater wires on the sensor side and saw 2.3 ohms. What is the correct resistance for the heater circuit on the A/F sensor? I searched this and other forums and I can’t find a definitive answer. For what it’s worth, the sensor was cold (engine hadn’t been run for about 8 hours). Wires look intact and all strain reliefs are OK. The car is a completely stock 2006 US model Impreza 2.5i and the sensor is the original factory unit. Thanks in advance.

- Walt

 

This is all that's available from the workshop manual without having a new sensor to hand

US MY06 2.5L non turbo P0031 diagnostics.pdf

 

Don,

Excellent. Thank you. The wiring diagrams should help if I have to dig a little deeper.

- Walt