CEL question
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Laughing Gas
Joined: Dec 2003
Posts: 752
Likes: 32
From: North Carolina
CEL question
My '10 STX 4.6 2v w/112,ooo mi has the CEL on . Had it checked at local AZ, as I suspected it was O2 sensor, passenger side. Cleared code to see if it would return, and it did. My next step will be to verify no vacuum leaks before I replace it. Now, my question, when either O2 sensor is causing a fault, and it is genuinely bad, not a vacuum leak or other issue causing it, how does the computer deal with this ? Does it go into a pre-programmed set of fuel and timing tables, or is it continually trying to resolve the problem by making real time adjustments ? I track pretty much every tank of fuel for mileage and have noticed no real appreciable difference. There is no difference in how it runs/drives and whether it be leak or faulty sensor, I will get it resolved in due time, just curious as to the details of how the vehicle deals with it on a day to day basis. Thanks in advance !
Laughing Gas
Joined: Dec 2010
Posts: 1,200
Likes: 45
From: Timbuk3, MI
The DTC may indicate that a sensor has detected in the system that there iis an out-of-range condition, HOWEVER, usually there are/could-be several possible causes (besides a vacuum leak) that need to be diagnosed and pinpointed prior to throwing parts are the situation.
What was the DTC?
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Goth 150
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What was the DTC?
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Goth 150
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Thread Starter
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Laughing Gas
Joined: Dec 2003
Posts: 752
Likes: 32
From: North Carolina
Forgot the exact code, did not write it down at first, since I will be checking for other issues first before I throw parts . Have not pulled it, but may pull it and test it as well before any parts are purchased. I'm in no hurry, as it drives just fine. I am still curious as to what effect it has either way, on how the engine management does its thing, but this may be dependent on the code.
Postmaster
Joined: Nov 2006
Posts: 4,517
Likes: 3
From: SE Wyoming
Can't answer without knowing the DTC. If the front O2 is throwing a code all it means is that the engine isn't burning clean enough OR the sensor is bad and not reading properly. If the rear throws throws the code it means the cats aren't working properly OR the sensor isn't reading properly.
If it is the rear there shouldn't be any change in the engine management, if it is a front then it may go back to a more "canned" way of mixing air and fuel. Vacuum leaks usually throw a 171 or 174 because they introduce air that is not measured at the intake and therefore make the burn too lean and the only sensor that catches it is the pre cat O2 sensor. A vacuum leak that throws those codes almost always causes idling problems at the very least.
If it is the rear there shouldn't be any change in the engine management, if it is a front then it may go back to a more "canned" way of mixing air and fuel. Vacuum leaks usually throw a 171 or 174 because they introduce air that is not measured at the intake and therefore make the burn too lean and the only sensor that catches it is the pre cat O2 sensor. A vacuum leak that throws those codes almost always causes idling problems at the very least.
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Laughing Gas
Joined: Dec 2003
Posts: 752
Likes: 32
From: North Carolina
I have had a rough idle issue, but only with the AC on for some time now and have chased the vacuum leak idea, but not very aggressively. I also changed plugs earlier this year and the outgoing plugs were completely clean, no residue in the slightest, making me think it was too lean, but both banks were identical. This led me to believe that perhaps reading plugs in modern Fuel Injected engine was not as simple as I first thought. This weekend should give me some opportunity to get in depth under the hood and see what's up.
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