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2005 LL Bean Outback Wagon, 2005 Outback Wagon Limited
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Discussion Starter · #1 ·
Hi All
I have searched and searched for something on this topic to no avail. I am getting the following codes P0031, P0037, P0043, P0051, and P0057. All pertain to the O2 heater circuit and low voltage. I have replaced all the sensors because of the age and figured I might as well do them all. These codes were present well before I replaced them. I cut the connector off of the old o2 sensors and plugged them in to check the 12 volts when the key is on and as best I can tell I am getting about 2.0-2.5 volts at all connectors where the O2 sensors plug in. Can anyone please tell me where I should be looking to correct this issue. I see no fuses relating to this issue in a 2005 outback with a 2.5 SOC. Please help, ready to roll it off into the woods.
 

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Look for damaged wires upstream. AFAIK the sensor heater circuit uses full system voltage (12-14V).

You need to verify that the ECU is making full voltage on that output, and then verify the wires that are supposed to carry it down to the exhaust.

I haven't got the 2005 wiring diagram, @plain OM probably has it handy though.
 

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@mduquette05

Can anyone please tell me where I should be looking to correct this issue. I see no fuses relating to this issue in a 2005 outback with a 2.5 SOC. Please help, ready to roll it off into the woods.
Don't roll it off, at least not yet!

With codes for five sensors, I'm presuming this is a CA-spec, with dual cats.

The "Low" fault on all five sensors suggests a single common cause.

The five sensors' heaters are powered by battery voltage, through SBF-5 and the A/F Sensor Relay. SBF-5 is a 30 Amp slow-blow fuse in the engine compartment fuse box.

The relay is located at the far right of the dashboard, in a column of several relays. (They can be seen by removing the right side trim cover of the dashboard, and looking forward.) However, the relays are rarely faulty. Moreover, in this particular case, the relay has two pairs of switching contacts; one for the two A/F Sensor heaters, and the other for the three O2 Sensor heaters. It's unlikely that both pairs of contacts would fail together.

Probably best to start with SBF-5. Remove and check it for continuity. (There's a locating diagram on the underside of the fuse box cover.)
While out, check that one of the two sockets that the fuse plugs into has battery voltage (even with the ignition off), measured relative to battery negative/ground.

Related (but important) connection question. Does the engine start and run? If it does run, then another relay (the Main relay) that is related to the sensor relay is okay, and any impact it might have on the sensor relay is eliminated. If it does not, then check SBF-7, in the same engine area fuse box. SBF-7 supplies the Main and the Sensor relay energizing coils. And, as above, check that one of the two SBF-7 sockets has battery voltage.

At the sensor connectors, there should be one wire (only) that has battery voltage when the ignition is at On. The front A/F Sensors have rectangular six-wire connectors (of which only four are used). I believe that at the front A/F Sensors (pre-cat converter) connectors, the wire carrying the battery voltage for the heater is white with a blue stripe (or dots). The wire should be at the lower left corner when looking face-on at the engine harness connector.

If one of the fuses is blown, there might be a problem (short) that caused the fuse to blow, and that might have to be investigated.

Also, sometimes the fuse blades and sockets develop corrosion and don't make good contact. Removing the fuse and plugging it back in sometimes clears the corrosion and re-establishes contact.

I've attached related (selected) wiring diagrams.

Let us know what you find, and if needed we can take the troubleshooting ideas further.
 

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Discussion Starter · #4 ·
SBF-5 was the culprit

Thanks plain OM. SBF-5 was the culprit removed it and could see a visible gap but put the meter to it to be sure and sure enough blown fuse. Robbed one from another outback I have and bang didn't even have to clear the codes. Drove it for a bit and was hoping this would also fix the low idle issue but it did not. The low idle issue started about the time the check engine light came on. Is this just a case of it needs to be driven to get the computer and O2 sensors back up to snuff? Any thoughts on the low idle with no codes? Thanks again for the help.
 

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Is this just a case of it needs to be driven to get the computer and O2 sensors back up to snuff?
Very possible. After the battery is disconnected, or codes cleared, or power lost to the backup memory in the ECM, it's not unusual for the engine to run poorly until the engine control unit relearns minor adjustments to the base controls. (There's a post somewhere here with more detailed instructions for "relearning".) Give it some time and then let us know.

I wonder why the 30 Amp fuse blew (showing a visible gap). SBF-5 connects to the switching contacts of the sensor relay, and from there to the A/F sensor heaters. It's not unusual for the fine wires in the sensor housing that connect to the heater (probably a ceramic rod) to come loose. Although there's insulation in the area, I guess it might be possible for the free end of the wire to touch part of the sensor housing, which is grounded. But it's all spec right now, and if the sensors are new, it's less likely that the problem will reappear.
 
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