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Old 03-21-2005, 02:23 PM   #1
doghouse
Scooby Newbie
 
Member#: 83500
Join Date: Mar 2005
Default p0031 --> O2 heater problem

Hello. I have a '97 Outback into which I have transplanted a '02 WRX motor. I've got about 40k miles on the setup and only now have gotten around to hooking up the OBDII and reading the codes. I have several, some which I am aware of, and some which puzzle me. There was no fuel tank pressure, temp, or level sensor or fuel pump controller circuit in the Outback, so all those codes are present (any ideas how to "fake" those?). But the one that really puzzles me is the P0031 --> Front O2 Heater Circuit. I've checked all the wires going back to the ECU, checked for proper voltage and grounding of the circuit, and even tried three different O2 sensors. All to no avail. Any ideas? Thanks.
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Old 03-21-2005, 10:21 PM   #2
xcntrk75
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Member#: 60224
Join Date: Apr 2004
Chapter/Region: MAIC
Location: NOVA
Vehicle:
2008 FXT Sports 2.5
Dark Grey Metallic

Default

Well are you sure your harness and ECU are from the same year? Reason I say this is that (from my research) the ECU pinout for the “Front Oxygen (A/F) Sensor” is different for the 02/03 from the 04/05 ECU’s. For example the sensor signal + (pin-19) and – (pin-29) is reversed on a 04/05 ECU. Possibly this is the source of your problem?

Rather than digging back into the wiring, if you have an extra O2 sensor kicking around, try swapping these signal wires and see if this corrects your issue.

As for the fuel issue. I'm surprised you even got it running without these sensors...
Seriously though, how are you controling the fuel pump, I assume you're using a WRX pump?
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Old 03-22-2005, 07:42 AM   #3
doghouse
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Default

Quote:
Originally Posted by xcntrk75
Well are you sure your harness and ECU are from the same year? Reason I say this is that (from my research) the ECU pinout for the “Front Oxygen (A/F) Sensor” is different for the 02/03 from the 04/05 ECU’s. For example the sensor signal + (pin-19) and – (pin-29) is reversed on a 04/05 ECU. Possibly this is the source of your problem?
Hmmm... I don't *think* so, as everything was labled, but I suppose anything is possible. There are also so many wires and different colors for me not to notice something like that. With Subaru's affinity for changing connectors every 6 months, I'd also be surprised everything plugged in.

Quote:
Originally Posted by xcntrk75
Rather than digging back into the wiring, if you have an extra O2 sensor kicking around, try swapping these signal wires and see if this corrects your issue.
Anything is possible and perhaps I should check this. Although I did backpin the connector at the ECU and it was within spec.

Quote:
Originally Posted by xcntrk75
As for the fuel issue. I'm surprised you even got it running without these sensors...
Seriously though, how are you controling the fuel pump, I assume you're using a WRX pump?
Oh, it runs like a top. It's got 40k already on the swap and not a single (real) problem. The pump is simply hardwired. Not safe in event of a wicked accident, but...

This is something I've been putting off for awhile (obviously) and finally am trying to wrap my head around. I'm not entirely sure what to do about the fuel tank pressure, level, and temp sensors. Perhaps find someone with an '02 and check to see what the ECU is looking for. I'm going to dig around in the rest of the harness (if I can find the box I saved it in) for the fuel pump controller. It's *possible* I still have that and can hook it up.

Thanks for the suggestions, I'll give that a try.
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