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Discussion Starter #1
About 2 weeks ago I changed out the plugs and coil packs in my '07 Santa Fe 2.7L due to a misfire on cylinder 1 (dead miss - failed coil pack). After putting it all together, everything was great - no more misfire, no CEL, etc. Then, about a week later it threw a CEL again for P0420 which is the first time this has happened on this car in 207K miles.

Reading through the forums I found a number of references to checking the voltage on the upstream and downstream OS sensors, so I plugged in my BlueDriver tool and captured what I think is the correct data. Specifically, with the engine at full temperature I monitored at idle for about 5 minutes and found OS sensor Bank 1 Sensor 2 showing about 0.76 volts (hardly moving) and Bank 1 Sensor 1 oscillating between 0.035 and 0.850 during that timeframe. Am I monitoring the right data?

Since replacing the plugs and coils the engine has been running perfectly - no misfires, hesitation, gas mileage where I expect it to be, etc. I did see a few references to these cars sometimes throwing a P0420 code after replacing the plugs and/or coils but I am not clear what the correlation would be. Since the car ran for several days with a dead miss on cylinder 1, what are the chances that I fouled a sensor which is now acting up? It seems coincidental that the cat would suddenly fail right after performing this work, but I suppose it's possible.

Any insight would be appreciated!
 

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Am I monitoring the right data?
Yeah, and the voltages sound OK...when the engine is fully warmed up at least.

BamBamNJ said:
Since the car ran for several days with a dead miss on cylinder 1, what are the chances that I fouled a sensor which is now acting up?
Your voltage measurement suggests the sensors are working properly. What I would do is monitor the 4 O2 sensor voltages from a cold start. See if the output from B1S2 matches that of B2S2, or does the bank 1 sensor continue to oscillate for a while after the bank 2 voltage has stabilised.

It seems coincidental that the cat would suddenly fail right after performing this work, but I suppose it's possible.
Ignition misfires are probably the most common cause of converter failure, so maybe driving it for several days with a dead coil killed it.
 

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Discussion Starter #3
Your voltage measurement suggests the sensors are working properly. What I would do is monitor the 4 O2 sensor voltages from a cold start. See if the output from B1S2 matches that of B2S2, or does the bank 1 sensor continue to oscillate for a while after the bank 2 voltage has stabilised.
Thanks for the info! I will set up monitoring for those items and log it when I head out later tonight. Hopefully that will provide me with more insight in to what is going on. If the cat is the issue, I almost wonder if it would be less of a problem if it were warmer out and the cat could get really, really hot to clear itself out.
 

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Your voltage measurement suggests the sensors are working properly. What I would do is monitor the 4 O2 sensor voltages from a cold start. See if the output from B1S2 matches that of B2S2, or does the bank 1 sensor continue to oscillate for a while after the bank 2 voltage has stabilised.


Ignition misfires are probably the most common cause of converter failure, so maybe driving it for several days with a dead coil killed it.

I ran this test a short time ago and logged the whole time. What I noticed was that after driving for about 20 minutes and then sitting at idle, both S1 sensors continued to oscillate (as I believe they are meant to) while both S2 sensors would stabilize (again, as I believe they should). Are both of my assumptions correct?

Additionally, what I did notice was that B1S2 stabilized roughly at 0.85 volts or so, while B2S2 hovered closer to 0.760 volts. Would this disparity be significant at all? Or would it be considered within the normal range? I watched a few videos on this topic and several people mentioned they expected to see voltage closer to 0.55 or so, but perhaps that was for their specific car.
 
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