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Old 05-19-2018, 03:33 PM   #1
austynn2001
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Default P0134 in an 02 WRX

Good afternoon, NASIOC. I'm in the process of trying to finish up a bugeye wagon for my wife. I got the car in pieces and rebuilt it over the last year or so. I finally got it up and running on a Clark Turner tune (due to the 2.2 block/2.0 heads and some other small things). I've got it to where it runs and drives pretty well and it actually passed state inspection last week. My last hurdle is this damn check engine light. The Accessport is showing a P0134 no activity on front o2 sensor. I replaced it with a brand new Denso and it came back on pretty quickly. I noticed that the wires had fallen down onto the exhaust, so I figured maybe I fried the wires. I ordered another, installed it with the wires away from the exhaust, and the code came right back. I looked at the wiring at the oxygen sensor plug and at the ECU and all looks well. I replaced the main relay (to rule it out, I like new parts and I like having spare parts) and that didn't do it either. I tested the heater circuit on the new o2 sensor. It shows about 2.8 ohms, which I believe is correct for a healthy sensor. When I tested between the ECU connector B137 (IIRC) and the o2 sensor plug (B18?) at their respective pins, I got roughly .6-.7 ohms on both. The Subaru manual indicates I should have less than 1. This tells me my wiring is fine. Are there any steps or anything I'm missing? Electricity is not my area and I'm trying to avoid dumping some gas on this thing lol
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Last edited by austynn2001; 05-19-2018 at 05:05 PM.
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Old 05-20-2018, 05:19 PM   #2
austynn2001
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Ok, I ran the car for a while and the blue signal wire will put out over a volt when it gets warmed up. If I run the car up to temperature, reset the ECU on the Accessport and start it up again, the p0134 seems to stay off. If I unplug the sensor with the car running, it throws the code for low voltage (p0131?). This is making me think that the heater circuit isn't being activated and it's telling the car there is no activity from the sensor. Is there a way to test the power coming from ECU to the heater wires in the o2 sensor?
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Old 05-21-2018, 09:11 PM   #3
austynn2001
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Anyone got any ideas on this?
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Old 05-21-2018, 09:41 PM   #4
TomHang
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Cool mate
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Old 05-22-2018, 10:35 AM   #5
PVNRT
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Not sure if I am much help but I know the heater circuit gets priority when you first start the car so it can keep emissions down during cold start....from what you say about bringing it up to temp then turning off code it sounds like you are in the right direction if code stays off when warm. But it may just be the exhaust itself brings it up to temp and the heater is bad.

Just brainstorming here but is it possible to start the car with sensor removed and actually touch it to see if warm before engine warms it? I don't know how hot they get so be careful. I believe the sensor will warm itself with the key on but engine off using straight battery voltage ,so maybe test that way.

I am still learning about tuning but is there any possible conflict between open loop and closed loop in your tune at startup keeping the sensor signal active but not turning on the heater?

Lastly make sure you are buying genuine Denso sensors...buying from Amazon or Ebay is about 50/50 chance of fake. They are so good at fakes now even the packaging seems legit.
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Old 05-22-2018, 12:10 PM   #6
austynn2001
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Quote:
Originally Posted by PVNRT View Post
Not sure if I am much help but I know the heater circuit gets priority when you first start the car so it can keep emissions down during cold start....from what you say about bringing it up to temp then turning off code it sounds like you are in the right direction if code stays off when warm. But it may just be the exhaust itself brings it up to temp and the heater is bad.

Just brainstorming here but is it possible to start the car with sensor removed and actually touch it to see if warm before engine warms it? I don't know how hot they get so be careful. I believe the sensor will warm itself with the key on but engine off using straight battery voltage ,so maybe test that way.

I am still learning about tuning but is there any possible conflict between open loop and closed loop in your tune at startup keeping the sensor signal active but not turning on the heater?

Lastly make sure you are buying genuine Denso sensors...buying from Amazon or Ebay is about 50/50 chance of fake. They are so good at fakes now even the packaging seems legit.
That was a help. I'll try plugging in the other brand new sensor I have and see if it heats up first to get an idea of whether or not the car is trying to heat it up. As far as anything tune related, I have no idea. The genuine sensors thing is a very good point that I also thought of last night. Both new "Denso" sensors I bought were from eBay and said new with no box. I figured the boxes just got damaged or lost or something because the sensors look good and say Denso on them like they should, but you never know. I ordered a real one last night just in case that's really the problem. I retorqued everything before the o2 sensor in the exhaust last night to rule any leaks out. I don't hear or feel any. Thanks for the advice. I'll be sure to report back with any updates. There's not a ton of documentation on this code online.
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Old 05-22-2018, 12:51 PM   #7
PVNRT
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After receiving a fake set of spark plugs from Amazon I only buy sensors and important stuff from Summitt or Jegs etc now. You may have authentic sensors already but they may be "generic" or even for a different car with different set voltages.

Ebay is ok for some parts but for sensors I don't go there anymore.

The spark plugs were identical to the real NGKs but the packaging was slightly off and they didn't have the white powder on the insulators like they are supposed to. You really gotta be careful nowadays where you source things large companies like Summitt would never jeopardize their relationship with manufactures and sell fakes.
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Old 05-22-2018, 02:48 PM   #8
austynn2001
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I emailed the tuner and he said that there is no p0134 code in the 02 ECU. That's the only code showing up on the Accessport. Now I'm even more confused.
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Old 05-22-2018, 02:58 PM   #9
subaru_gc8
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Quote:
Originally Posted by PVNRT View Post
After receiving a fake set of spark plugs from Amazon I only buy sensors and important stuff from Summitt or Jegs etc now. You may have authentic sensors already but they may be "generic" or even for a different car with different set voltages.

Ebay is ok for some parts but for sensors I don't go there anymore.

The spark plugs were identical to the real NGKs but the packaging was slightly off and they didn't have the white powder on the insulators like they are supposed to. You really gotta be careful nowadays where you source things large companies like Summitt would never jeopardize their relationship with manufactures and sell fakes.
IMHO you should never buy electronics from anyone other than Subaru. after market parts are a 50/50 crap shoot if the part will work or not. and you figure, if you are using the part for calibration, there are standards that need to be met as to what each voltage point means. So if you are using ar part that has a different calibration, it will throw your tune off with it. but yeah.... i use oem for o2 sensors, Mafs, Maps especially.
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Old 05-22-2018, 07:10 PM   #10
austynn2001
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Well. I plugged in an old-new "Denso" sensor. Turned the key on. Not even luke warm. I then pulled the sensor and got the meter out. I get 12v at the y/r wire at the o2 sensor plug with the key on. That tells me that the ECU is sending heater power. The bad news came when I found my copy of the 02 WRX service manual and looked for the troubleshooting for p0134. The tuner was right. There's no p0134. There is, however a p1134. That one says to replace the ECU. I have a feeling the Accessport is trying and failing to show me p1134. FML. I'm still going to give this new sensor a try before I order an ECU, but it's not looking good for my wallet.
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Old 05-22-2018, 08:26 PM   #11
PVNRT
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Another option.....if you have a wideband and it reads normally is just to turn off that code but I am not sure if Cobb gives out accesstuner anymore to the public to do that. I am an opensource guy so I am not sure.

Problem is the ecu will need that front 02 sensor during warm up and cruising. I would try an opensource flash before you junk the ecu....just a thought


Make sure your AP is up to date and syncs with the correct model year if you are going to stick with it.
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Old 05-25-2018, 06:58 PM   #12
austynn2001
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Genuine Denso for the win! No more check engine light. Car goes in for paint in the morning and I don't need to buy an ECU! And it's a long weekend. Thanks for the help guys.
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