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Discussion Starter #1
Here's the skinny - about 4 weeks ago - installed TB and random cat and rerouted intake ducting. On stock tune, got a O2 sensor code - P0133 about 4 days after installation. Installed Waynes tune - idled like crap, stalling so I ditched his tune. Been back on stock tune about 2 weeks. running basically like factory, stalling now and again at idle spontaneously.

Out of the blue yesterday, the thing belches codes. Got P0133 again for O2 sensor
Got P1246 for the first time - something about generator/regulator - what is this? And to the titile of this post, does it have anything to do with the flickering dash lights that this car has always had?

Quickly, regarding O2 sensor, it doesn't make sense why I can clear the code and it doesn't come back on for a week or more. The thing costs about $80-100 to replace, so I don't want to replace it if I don't have to. I'd use Wayne's tune to just turn it off, but the guy is a PITA to get a hold of.

Starting to hate my car.......
 

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I just had my 02 sensor replaced at dealer, and it was throwing 3 or 4 more codes that weren't adding up. Since replacing it i haven't had a CEL. I'd say you should probably replace it, or get around it like you said with Wayne. It just seems like when it goes it starts a spiral of codes, at least in my experiance.
 

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The Librarian
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Moved to ”Ford Focus Technical Chat”

O2 sensor and flickering lights most likely aren't related.
Flickering lights could be sign of a weak alternator though. [:(]
 

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Discussion Starter #4
Yeah - didn't think O2 sensor and lights were a thing.

The flickering lights are the dash lights and interior lights when at idle. I thought this topics has come up before but couldn't find anything on it. It only happens at idle and I wondered if the P1246 code had anything to do with the flickering.

Would the O2 sensor be under warranty? I did change to a random cat - will that void the warranty on the O2 sensor, if covered?
 

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The Librarian
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Flickering dash lights at idle are part of the YRF0 (updated ECU reflash TSB).
P1246 - Generator Load Input Failed (All Others) The PCM monitors generator load from the generator/regulator in the form of frequency. The frequency range is determined by the temperature of the voltage regulator where 97% represents full load, below 6% means no load. Generator circuit short to GND
Generator circuit short to PWR
Generator circuit open
Generator drive mechanism
Damaged generator/regulator assembly
Damaged PCM
Verify battery voltage is 14.5V.
Verify generator/regulator has the correct part number.
Sounds like alternator or battery isn't up to the task.
I'd get them checked.

I did change to a random cat - will that void the warranty on the O2 sensor, if covered?
I doubt the Dealer's going to cover that with the RT on there.
If you have the stocker, put it back on before you take it in.[;)]
 

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Discussion Starter #6
Whether or not I use an aftermarket tune, should I have the ECM updated to YRFO? How does the tune fix flickering lights? The code description mentions some groudnig issues - anything I should check with grounding?

Putting the original cat back on is a PITA but do-able if I have to. If it's not fueling correctly, is it possible that the O2 sensor will get fouled again? If it's not fueling correctly, shouldn't both O2 sensors have problems, not just the rear one?

Many questions, few answers - never a good sign....
 

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"it doesn't make sense why I can clear the code and it doesn't come back on for a week or more."

Some codes, to avoid falsing, require a condition to exist for a certain time, miles, and/or start-stop cycles before setting a code and throwing a CEL. I believe the second O2 sensor is there just to monitor whether or not the cat is functioning properly. No guarantees, but I have a sneaking suspicion that if the original cat is put back on, the O2 code will no longer be thrown.
 

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If your car runs like poop at idle and cruise, you need to replace the 02 sensor. Its a serviceable item and its not a major issue that it went out. It happens. Mine went at 40K. The flickering lights and generator code...REPLACE your alternator before it burns up; ie catches on fire like mine did. I actually had mine rebuilt for ~$100. Two problems, and they are unrelated.
 
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