rear Oxygen sensor question

bigdweeb · 04-04-2004, 11:34 AM

I am getting a CEL... pretty sure it's a PO420, but I haven't had it pulled since I changed some stuff around.

Here's what I have: Borla Headers -> RandomTech Cat -> Stromung midpipe -> Prodrive muffler

The rear o2 sensor had to be replaced and my only option at the time was a universal fit Walker rear oxygen sensor. The sensor didn't come with instructions for how to wire a Subaru 4 wire connector, only the old 3 wire style, even though their product guide said it was supposedly the right sensor.

I have been trying to track down the wiring pinouts for the OEM sensor to make sure I wired it up properly but can't seem to find them. I checked my shop manuals and I didn't see a description of the wires. I have been searching all morning but haven't found anything that seems to match what I have.

The stock sensor I have is a Bosch and has A24-A71 057 98010 on it. There are 4 wires on it: 2 white, 1 grey, 1 black. The 2 white should be the heater wires (polarity independent). I am trying to confirm which of the other 2 is ground and which is signal to the ECU.

Anyone out there have a clue?

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gavinl · 04-04-2004, 07:03 PM

The grey wire is signal and the black is ground.

If you want to completely bypass the rear O2 sensor I have a bypass that I construct that can do that.

bigdweeb · 04-05-2004, 12:48 PM

I would rather get the stupid thing working again if possible... it's mostly on sheer principle at this point. What does your bypass entail? Is it similar to the Pony Express MIL Eliminator?

I think I may have made the opposite assumption that the grey wire was the ground due to its position on the sensor. I looks like it comes out of the side instead of the back like the other 3. I think that was the logic I used anyway. I will have to crawl under the car again to see for sure. If I did miswire it, I hope it's not busted from being miswired all this time.

gavinl · 04-05-2004, 09:33 PM

Yup, what I rigged is similar to Pony Expresses Mil Eliminator.

Being a 1v signal device, I don't think you'll bust the O2 sensor if wired opposite. Check it out and see if the wires were indeed reversed.

04-04-2004, 11:34 AM	#1
bigdweeb Scooby Specialist Member#: 31035 Join Date: Dec 2002 Chapter/Region: NESIC Location: Boston Vehicle: 13 Ford Explorer 13 Mazda3 Skyactiv	rear Oxygen sensor question I am getting a CEL... pretty sure it's a PO420, but I haven't had it pulled since I changed some stuff around. Here's what I have: Borla Headers -> RandomTech Cat -> Stromung midpipe -> Prodrive muffler The rear o2 sensor had to be replaced and my only option at the time was a universal fit Walker rear oxygen sensor. The sensor didn't come with instructions for how to wire a Subaru 4 wire connector, only the old 3 wire style, even though their product guide said it was supposedly the right sensor. I have been trying to track down the wiring pinouts for the OEM sensor to make sure I wired it up properly but can't seem to find them. I checked my shop manuals and I didn't see a description of the wires. I have been searching all morning but haven't found anything that seems to match what I have. The stock sensor I have is a Bosch and has A24-A71 057 98010 on it. There are 4 wires on it: 2 white, 1 grey, 1 black. The 2 white should be the heater wires (polarity independent). I am trying to confirm which of the other 2 is ground and which is signal to the ECU. Anyone out there have a clue? * Registered users of the site do not see these ads.

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04-04-2004, 07:03 PM	#2
gavinl Scooby Newbie Member#: 57891 Join Date: Mar 2004 Location: Dublin, OH Vehicle: 2005 9-2x Aero Black	The grey wire is signal and the black is ground. If you want to completely bypass the rear O2 sensor I have a bypass that I construct that can do that.

04-05-2004, 12:48 PM	#3
bigdweeb Scooby Specialist Member#: 31035 Join Date: Dec 2002 Chapter/Region: NESIC Location: Boston Vehicle: 13 Ford Explorer 13 Mazda3 Skyactiv	I would rather get the stupid thing working again if possible... it's mostly on sheer principle at this point. What does your bypass entail? Is it similar to the Pony Express MIL Eliminator? I think I may have made the opposite assumption that the grey wire was the ground due to its position on the sensor. I looks like it comes out of the side instead of the back like the other 3. I think that was the logic I used anyway. I will have to crawl under the car again to see for sure. If I did miswire it, I hope it's not busted from being miswired all this time.

04-05-2004, 09:33 PM	#4
gavinl Scooby Newbie Member#: 57891 Join Date: Mar 2004 Location: Dublin, OH Vehicle: 2005 9-2x Aero Black	Yup, what I rigged is similar to Pony Expresses Mil Eliminator. Being a 1v signal device, I don't think you'll bust the O2 sensor if wired opposite. Check it out and see if the wires were indeed reversed.