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First track day was great. 5 20 minute sessions. Learned alot from my car and what it's capable of. Was told by my instructor that I'm a natural and I act like I have years of experience. So thats great. I was drifting around corners that most don't. drifting isn't always the fastest way. I was pushing the absolute limits of my car and pushed it too far mid drift and slid sideways into the grass. No damage at all and everything was good. Finished the rest of the track and go to my parking spot. Let the car sit around 20 minutes. Start the car and after about 5 minutes of idling, check engine light comes on. Go to autozone and they say its a P0138 O2 Circuit High Voltage (Bank 1, sensor 2). So it's an O2 sensor gone bad now?

Any idea why its all good and then all of a sudden its bad? Doesn't make sense to me. In assuming I need to go to an autoparts store tomorrow and get the O2 sensor and replace it? Is it the 1 connected to the downpipe, or the other one?

I have the Phase 2 tune with CEL delete. After I change the O2 sensor, will the light go off on its own? I've tried every way to reset it and it won't and autozone said they wont clear it for me.

NASA track and dragstrip in Millington TN United States.
 

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The O2 sensor in question is the one post-cat / downpipe (not the important O2 sensor). Try clearing the code with a scanner and see if it comes back.

I've gotten voltage related CELs due to my car sitting for two weeks, with plenty of parasitic draw in between (since I was working on it) -- weak batteries will cause this. Cleared it and it never came back.

Strange that the CEL would pop after a bit of idling. Normally these voltage CELs happen when the engine turns over and does its checks. I wonder if your O2 sensor shorted somehow at that moment and sent that signal to the ECU.
 

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The more exotic the car, the worse the parasitic draw is. Battery conditioners are a mandate if not driving like every other day.
 

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I'm afraid you drive an Alfa, so weird faults are a fact of life.... Generally the 4Cs are fairly reliable, but you do periodically have "random" faults and every user seems to have different ones (but there are some common ones - Dash delaminate & DCT issues). As a result, I always carry a scanner so I can reset or deal with "most" issues. I have only ever had one issue which has prevented me from doing a track weekend. I drove the car down (80 miles) to the track, and when I started it up for my session the gas peddle sensor failed...

So there are some basic reset methods. Sometimes you get kicked out of race mode (or dynamic), and some errors will allow you to go back into those modes without turning off the engine (ESC Fault is one of those errors - and I have those about once a track weekend). Some errors, can be cleared via a engine shutdown and restart. Sometimes reset requires a battery pull or or 3 restarts. The last fault clear method is a CAN tool. If it is a "real" fault, then you might be able to clear, but it comes back quickly.
 
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Discussion Starter #5
I'm afraid you drive an Alfa, so weird faults are a fact of life.... Generally the 4Cs are fairly reliable, but you do periodically have "random" faults and every user seems to have different ones (but there are some common ones - Dash delaminate & DCT issues). As a result, I always carry a scanner so I can reset or deal with "most" issues. I have only ever had one issue which has prevented me from doing a track weekend. I drove the car down (80 miles) to the track, and when I started it up for my session the gas peddle sensor failed...

So there are some basic reset methods. Sometimes you get kicked out of race mode (or dynamic), and some errors will allow you to go back into those modes without turning off the engine (ESC Fault is one of those errors - and I have those about once a track weekend). Some errors, can be cleared via a engine shutdown and restart. Sometimes reset requires a battery pull or or 3 restarts. The last fault clear method is a CAN tool. If it is a "real" fault, then you might be able to clear, but it comes back quickly.
Just bought a scanner from Walmart. Has the option to clear codes. I tried and it didn't. Its showing the p0138 code and p0687. At O'Reilly's about to buy the O2 sensor if they have it.
 

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+1 on this.
Has cleared ESC codes on the 4C but did not on a Honda that someone on track was having an issue with. Figure that???

But it is small and works with a phone app. I keep it in the “glove box” of my track car so it is always handy.

I don’t get too many codes, but every once in a while. Odd that a tune with CEL delete shows an O2 sensor-related code.

Let us know if you can find an aftermarket sensor. At least this one is easy to get at. Sensor 1 is a pain in the arse. But OEM comes with a specific length whip and connector. So unless that is standard on some other FCA vehicles (likely is), you may be off to the dealership. These are not cheap there. Oh, and they can be a difficult to get out of their sockets.

Did you figure out the other code? If totally un-related, then I would suggest battery or connections before swapping the sensor.

Good luck.
 

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Random google search returns:

A P0687 code is stored when the PCM (powertrain control module) detects an incorrect, abnormal, or erratic voltage reading from the relay control circuit that supplies it with its power.

I would check battery terminal connections first, and have battery tested if it persists.
Does not seem likely that you have two real voltage-related issues at the same time.
 

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Discussion Starter #9
So I took the computer off and reset it like normal. Code was gone. Drive around a few minutes and nothing. Turn the car off after getting gas and it comes back on. Use the scanner and it only comes back to the p0138 code and its able to erase the code this time. Driving it and turning it back on and off a few times with no issue. Maybe it is the battery.
 

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So I took the computer off and reset it like normal. Code was gone. Drive around a few minutes and nothing. Turn the car off after getting gas and it comes back on. Use the scanner and it only comes back to the p0138 code and its able to erase the code this time. Driving it and turning it back on and off a few times with no issue. Maybe it is the battery.
Yes it happened to me when I drove my 4C hard at the race track and went over some rough bumper edging. The CEL went on and when I checked the battery terminal the positive ring terminal had loosened from its
post and was loose. Once I tightened it everything worked fine and CEL was gone.
 

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Its my daily so I dont think that's my issue right now. About to have my battery tested.
However, a partially corroded battery terminal can cause all kind of issues. Our cars are very sensitive on battery voltage. Several car have had this issue, so be sure your terminals clean and the cables well secured!
 
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Discussion Starter #13
O'Reilly's shows me 1 O2 sensor for $270, but can't tell me which one it is.

Napa doesn't sell either, and can't even get a new battery for me.

Autozone can't sell me either as well.

The Alfa Dealership here is awful so I'd rather not have to deal with them. The next dealerships are 2 and 3 hours away.
 

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Discussion Starter #14
The O2 sensor in question is the one post-cat / downpipe (not the important O2 sensor). Try clearing the code with a scanner and see if it comes back.

I've gotten voltage related CELs due to my car sitting for two weeks, with plenty of parasitic draw in between (since I was working on it) -- weak batteries will cause this. Cleared it and it never came back.

Strange that the CEL would pop after a bit of idling. Normally these voltage CELs happen when the engine turns over and does its checks. I wonder if your O2 sensor shorted somehow at that moment and sent that signal to the ECU.
Battery terminals are super clean. Do you perhaps know the part number for the o2 sensor? If its the one that's connected to the CAT(now downpipe) so not looking forward to having to take the cooling shroud back off. Ill probably leave it off this time because its such a hassle and it took me cutting it 1/3 and have help putting it back on.If its the other one, it should be a breeze.
 

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Looks like I found it on rockauto. Will be ordering 1 of these soon.
I believe this is not the proper connector. I ran into some issues on track a couple weeks back. The downpipe got loose and the leaky exhaust literally melted the 02 sensor wiring, causing a short and an error code similar to you. I bought Bosch 17212 o2 sensor that should be the proper connector but I havent installed it yet so I can't tell you 100% but im fairly confident
 

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The O2 sensor after the catalytic converter part number is 68239705AA

I got mine from EuroCompulsion many years ago.
 
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Did they test your battery?
It doesn't make sense that you are suddenly getting all of these codes. Either a harness plug or ground has come loose somewhere, or there's a voltage issue.
 

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Did they test your battery?
It doesn't make sense that you are suddenly getting all of these codes. Either a harness plug or ground has come loose somewhere, or there's a voltage issue.
Nope, they didn't test it because they didn't want to take it off the car and they said they couldn't find the cold cranking amps so without that they wouldn't know if its good or not.

I have found a pattern though. At least with the other codes. If I try to scan the codes with the E brake on, thats when it gives me all the extra codes. If I scan it with the E brake off, the only code it gives me is the o2 sensor code.

I can still drive the car in any mode with the scanner saying I have the o2 sensor code, its only when it randomly decides to throw the CEL is when it goes into limp mode. And even in limp mode, it still feels like it has plenty of power.

I finally found a place that work on my car, but they said their labor rate is $150 an hr and they have to order the parts so im looking at $700 to change both o2 sensors. So no thanks, ill change it myself and deal with the hassle and hope that fixes it.
 
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