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About 45 seconds after I start the car, it just stops running. It putters and fights, but just stalls. After I restart, it never stalls again until it sits for a while. I am reading code P0420 as well. I called a local AM radio car show and they said the cat converter and the stalling should be independent events and to replace the electronic throttle bottle, which I did, and it still stalls. Maybe I need to calibrate?? I'm a DIY newbie and I am struggling here. Any thoughts please?
 

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That is going to be a bad sensor or up to a bad pcm. When you first start the car it doesn't read the upstream 02 sensor or maf until about a minute or more depending on temperatures but goes off of pre determined values. You are tricking the computer into driving the car basically by skewing those temperature readings when you restart it so it will run off of those factory set values until it reaches a range where it can calculate fuel ratio/ temperature for maximum fuel economy. You do need to do an idle relearn procedure for a new throttle body but, that's probably not the issue. If you want to trick it into running all the time you could probably just disconnect the upstream 02 it will throw a check engine light and run rich but its kind of dangerous to be running the car the way you are because chances are when the computer catches up it will probably stall u could lose power steering.

Bear with me this post is getting long

So your throwing a P0420... Catalytic converter below efficiency.
The upstream 02 sensor is reading more oxygen than the downstream which is reading.... less oxygen than expected that is probably because your upstream 02 sensor is bad.... the downstream only measures efficiency and does not control the engine in any way. You also may have a bad cat depending on whatever year gm product this is but that wont cause the engine to stall unless the catalyst material is totally blocking the exhaust. I would also guess a maf that is bad but the slot type are very durable and or a map sensor or next a air temperature sensor.
 

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About 45 seconds after I start the car, it just stops running. It putters and fights, but just stalls. After I restart, it never stalls again until it sits for a while. I am reading code P0420 as well. I called a local AM radio car show and they said the cat converter and the stalling should be independent events and to replace the electronic throttle bottle, which I did, and it still stalls. Maybe I need to calibrate?? I'm a DIY newbie and I am struggling here. Any thoughts please?
That is going to be a bad sensor or up to a bad pcm. When you first start the car it doesn't read the upstream 02 sensor or maf until about a minute or more depending on temperatures but goes off of pre determined values. You are tricking the computer into driving the car basically by skewing those temperature readings when you restart it so it will run off of those factory set values until it reaches a range where it can calculate fuel ratio/ temperature for maximum fuel economy. You do need to do an idle relearn procedure for a new throttle body but, that's probably not the issue. If you want to trick it into running all the time you could probably just disconnect the upstream 02 it will throw a check engine light and run rich but its kind of dangerous to be running the car the way you are because chances are when the computer catches up it will probably stall u could lose power steering.

Bear with me this post is getting long

So your throwing a P0420... Catalytic converter below efficiency.
The upstream 02 sensor is reading more oxygen than the downstream which is reading.... less oxygen than expected that is probably because your upstream 02 sensor is bad.... the downstream only measures efficiency and does not control the engine in any way. You also may have a bad cat depending on whatever year gm product this is but that wont cause the engine to stall unless the catalyst material is totally blocking the exhaust. I would also guess a maf that is bad but the slot type are very durable and or a map sensor or next a air temperature sensor.
Thanks for the reply! 2 questions please:
1) Do you know the calibrate procedure for the new throttle body by any chance?
2) If the issue is an 02 sensor or BCM etc, wouldn't that show up on the diagnostic scan when I run it? Like a separate code than the P0420?

Appreciate your time!
 

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1) Do you know the calibrate procedure for the new throttle body by any chance?


Appreciate your time!
From the 2014 GM Repair Manual for both 4cyl and V-6:

Start and idle engine for 3 minutes, high idle will start to decrease to normal.
Ignition off for 60 seconds.
Start and idle engine for 3 minutes,
Drive and watch for normal idle, repeat procedure if necessary, clear all codes.

If you suspect an out of range O2 sensor replace both, they are a normal maintenance. items.
 

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The 0420 code is basically the o2 sensor code for a downstream sensor but yea there is codes for bad 02 sensor like circuit high circuit low voltage and it gets extreme like circuit slow response, no activity, high resistance ect.. but when the heater goes out inside the 02 sensor it probably wont throw a code or when its just burned or out of range. This problem could be un related and could even be a maf or any other sensor related to fuel injection. The pcm can be bad or wiring and its possible to have no codes.
 

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Possible engine temp sensor out of range but not far enough to trigger a code. If sensor tells PCM engine is warmer than it really is it will lean stall. No issues with a warm engine makes me suspect that.
Scan tool that can read what sensor see's vs temp. gun check of engine will confirm that.
As other said O2 sensors are wear / maintenance items especially if your mileage is over 80k miles.
Doing your own repairs the investment in a good scan tool is money in the bank. One saved trip to a shop pays for a good scan tool that can read what sensors are reporting to the PCM. Code reader is just a bare basic tool, scan tool is a must.
 
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