Help with o2 sensor heater circuit please!!

[HawkeyeLawrence]

Hi all,

I'm currently having a massive headache with my upstream o2 sensor heater circuit.

I had the P0031 code pop up a few months ago, with no other codes. I foolishly bought a replacement o2 sensor, fitted it and code is still there, even after clearing.

I tested the voltage at the connecter from the car and found it to only be 9v. I managed to test this all the way back to the grommet in the firewall and was getting 9v there aswell.

I tried tracing the wires on the inside of the car but was absolutely hopeless- too much in the way!

I'm hoping somebody has experience with this or has access to the subaru tech manuals- if so please help as i'm losing my !Removed! mind!

Cheers in advance [emoji106]

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[savage bulldogs]

Are you sure its definitely a fault with the sensor and not just the sensor reading?

if it's over or under fuelling could it just be flagging up a o2 sensor code maybe?

If it's not broke .....upgrade it 😊

[HawkeyeLawrence]

I don't think so... The code is for the heater circuit not the actual reading, and it's the only code present [emoji20]

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[savage bulldogs]

Only guess I had I'm afraid, cos I'm not bad with a spanner but sparky work isn't my bag bud .

If it's not broke .....upgrade it 😊

[Phillip1993]

It's most likely the ground that's at fult have you tryed test from the O2 sensor pos to a good ground like the Battery

[HawkeyeLawrence]

Great minds think alike! Just tried from the connector +ve to chassis and i've got 12v! Now I know it's the ground, just got to try and see where that pesky -ve wire goes after it disappears through the bulkhead...

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[Phillip1993]

From what I understand it goes to a pin on the ecu along with I a fue other sensors it could be where thay contact together before thay get to the ecu and i'm not sure where that would be on your car but if all is lost you could put your own ground in

[HawkeyeLawrence]

In that case i'll dig the ECU out, if nothing obvious there i'll try and follow the loom back as far as possible... If I made my own ground would the ECU throw a code as it's not detecting the correct voltage..? Or maybe it reads the voltage on the positive side... Electrics confuse the hell out of me!

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