P0431 code

  #1  
Old 06-02-2015, 08:39 PM
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Default P0431 code

Hi. My father in-law has an '02 Vue 3.0. It has a P0431 code, which we've tried rectifying by replacing both O2 sensors on bank 2 and cleaning all connections, which were then treated with dielectric grease.

The code remains despite our best efforts. Any ideas where we go next?

Thanks
 
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Old 06-02-2015, 10:02 PM
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How many miles? Catalytic Converter may be going south.

Good video that may help for self testing your converter(s).....
 

Last edited by tooter1; 06-02-2015 at 10:14 PM.
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Old 06-03-2015, 12:57 AM
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scary lookin dude

will check out vid on the morrow
 
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Old 06-03-2015, 06:05 AM
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Hi. There are about 150,000 miles on it, which is probably more than enough for the Cat!
 
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Old 06-04-2015, 01:11 AM
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His methods regarding interpretation of the expected behavior of the O2 sensors is correct. Note in there somewhere he adds a big disclaimer that after all that, you can't rule out the O2 sensor is not bad.

He seems to overlook that a partially plugged cat will retain heat near the outlet as the flow of the exhaust is impeded and it will raise temp due to reduction in flow

Do you have the ability to view real time data? Rear 02 behavior with a new rear 02 should yay or nay the cat

Never seen this code before. Seems to me that it is too much of a coincidence that both O2s failed at the same time but now you've removed 2 variables so it's either the cat not warming up fast enough (I guess measured by when the rear O2 begins to send readings.)

Never put dielectric grease on O2 sensor connectors. The sensor needs to use the atmosphere as a ref point and is vented. If dielectric grease finds its way to the vent and plugs the vent, the readings will be hosed.
 
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Old 06-04-2015, 06:39 AM
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Thanks for the reply. Just to clarify, we put the grease on the electrical connectors (black multi-pin plugs) that supply power to the sensor, not the sensor itself. If it is that the cat isn't warming up sufficiently how would this be rectified as that's what we're beginning to think it could be.
 
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Old 06-04-2015, 08:08 AM
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The only other thing I can come up with is that something else further upstream is tweaking the air/fuel mix such that the exhaust gases are not as hot as they should be.

What's the maintenance interval for the plugs on the vehicle? Have they been changed?

Or it is indeed a sad day for your cat.

Personally I would explore all other options (as you are doing) besides the cat. If you've eliminated everything else, that leaves the cat.

Access to a scan tool with real time data readouts might be helpful to see if the fuel trim is skewed and maybe it's running lean so the exhaust is not as hot as it would normally be. It's not bad enough to throw a lean code but it might be the difference when you have an older mostly spent cat.

These are GUESSES. Just don't want to see you blow money on a cat and have it not solve the problem. Then again you may have to spend money on a cat to solve the problem.
 
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Old 06-04-2015, 08:32 AM
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We changed all 6 plugs and rear coil pack assembly, possibly the most difficult plug change on any car ever made, gave it an oil change and a general service. Thing is, it runs beautifully. You wouldn't know there was anything wrong. The only thing I'm sure is faulty is the fuel cap, which doesn't appear to seal properly even though we've replaced it with an OEM part.
 
  #9  
Old 06-04-2015, 02:56 PM
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Clean that flange on the gas filler neck real good. Sometimes that's all it takes. And take a good look at the gasket. Maybe it's torn.
 
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Old 06-04-2015, 03:18 PM
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Originally Posted by Rubehayseed View Post
Clean that flange on the gas filler neck real good. Sometimes that's all it takes. And take a good look at the gasket. Maybe it's torn.
Thanks. Is that gasket on the filler cap or the fuel filler on the tank?
 

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