I received the following 2 codes late last year:

 

P0030

Heated oxygen sensor heater control circuit Bank 1 Sensor 1

 

&

 

P0134

Oxygen sensor circuit no activity detected Bank 1 Sensor 1

 

After resetting the codes about 2 or 3 times, I replaced my Upstream O2 Sensor.  No issues until just recently.  Only this time I got the P0134 code alone.  Either way, it's pointing me to the same O2 Sensor I just replaced.  Before I purchase another, more expensive O2 Sensor - are there any other areas 'pre-upstream sensor' I should be looking in to?

 

Sidenote 1

When the code popped up most recently, I removed the Sensor and cleaned with a wire wheel and replaced.  Checked all contacts for resistance and continuity.  Everything looked good and about 2 days later the CEL went out and didn't come back for about a month (where I'm at now).

 

Sidenote 2

I burn a full quart of oil in between Oil changes (every 4,000 mi.).  I mention this because I worry I may have the beginning signs of an internal head gasket leak (oil transfer between galleys and cylinders) which may jack up my combustion and fowl up O2 sensors.  Just a thought though, I can't be sure of this as there seems to be no smoke from the rear at start up.

 

Regards,

details on car?

 

what brand sensor?

^{Having both codes at the same time suggests a wiring harness problem.}

 

^{P0134 could be a fouled sensor.}

^{You should be aware tat O2 sensors foul externally too.}

^{I had a mercedes that would foul any brand of sensor in a month from an oil leak that wicked along the wiring harness}

^{until it reached the O2 sensor.}

 

^{Sensor brand is irrelevant.IME.}

Edited April 3, 201511 yr by naru

Year model engine?

 

Sensor Brand does matter. A cheapo sensor is more likely to fail because of an internal fault/defect.

 

A quart of oil in 4,000 miles isn't a huge deal, but if the PCV valve is old, it's a good idea to replace it with a new Subaru PCV. A worn PCV valve can cause increased oil consumption.

 

 

Sensor Brand does matter. A cheapo sensor is more likely to fail because of an internal fault/defect.

 

 

 

 

 

 

 

Not in my experience.

details on car?

 

what brand sensor?

- 2008 Outback Legacy 2.5i MT (Base model)

- 105k mi.

 

Not sure what other details you were curious about.

 

The sensor that I suspect is failing is a Denso - which I believe is the OEM brand.

 

Year model engine?

 

Sensor Brand does matter. A cheapo sensor is more likely to fail because of an internal fault/defect.

 

A quart of oil in 4,000 miles isn't a huge deal, but if the PCV valve is old, it's a good idea to replace it with a new Subaru PCV. A worn PCV valve can cause increased oil consumption.

I'll have to wait until later to check the exact engine model, got my 8 mo. year old son with me right now and mom's asleep.  Can't really make my way to the garage just yet.

 

I'm willing to buy a good sensor, but which one would you suggest?  I thought I got a good one the first time.  Rock Auto does have a Bosch with an orange cable  for about $140.  I believe its the one that was on there before I changed it the first time.  The Denso has a black cable.

Year

Model

Engine

Denso would be preferred.

 

Could there be rodent-chewed or otherwise damaged wiring from that area of the car?

Check your harness connections. No bent or fouled pins, or torn insulation.

There are resistance values between the ecu and harness. Check under

Subaru DTC codes for more info in this regard.

Did you get the direct fit or the universal type?

 

O.

Denso is the normally recommended brand for these, as well as for most other Japanese and Asian vehicles. I normally try to use Denso, but if I can find the manufacturers name on the original sensor on the car I match the brand with that sensor.

 

Double check the connector and make sure the pins are clean and it's clicked together all the way.

Im going with the connectors on this one, otherwise we have to start going back to the ECU as an issue.

Just dealt with the P0030 on my mom's 03 Outback. It had been popping up intermittently for the last couple years and we had replaced the sensor with a new denso one. Well, it came on permanently last week. As soon as it was cleared it would pop back up. So I found the old sensor (which I had kept labeled in its box in my parts heap because I suspected it was possibly not faulty) and plugged it in. By cutting the insulation on the spare sensors wires we checked the voltage to the sensor's heater, 12v on both leads, so it wasn't getting a ground. The ECU only grounds it with the engine running by the way, turning the key to run without starting it is not enough. So since the problem was between the sensor and the ECU ground, I pulled the carpet and ECU. I happened to have a spare ECU from a 03 legacy GT in the parts heap, so I plugged that in just to test before bothering to check the pins at the ECU connector. Eh voila, the sensor heated up! I put the Outback ECU back in, no sensor heat. So the switched connection to ground inside the ECU was gone. It's running on the spare GT ECU now and no codes.

 

If the sensor isn't being heated up, then it doesn't read accurately. That would set the P0134 inactivity code.

 

So check the resistance value of the heater at the sensor's plug, make sure it's getting 12v, and then check the corresponding pin at the ECU with the sensor plugged in to make sure that the 12v is making it all the way to the ECU before condemning the ECU.

Thank you everyone for your help!  I will begin diagnostics ASAP.