If you take note of the highlights and make comparisons you would see that B1S1 (bank one, sensor one, upstream) shows rich, while B1S2 the downstream sensor on the same bank shows that its lean. There are a couple reasons that could cause that to occur, one would be an exhaust leak between the sensors and checking for that none was found.
Let's look at the other bank now. B2S1 is showing that it's lean, while B2S2 is showing that it's rich. Now unless there is a sensor or circuit issue that really doesn't make any sense.
So how could we rule out a sensor issue from the front seat of the car? A hard acceleration drives the system rich, and both upstream and downstream sensors reported the condition correctly. A closed throttle decel then results in a fuel cut-off or extremely lean and all of the sensors reported that correctly as well. So at that point one or more could still be innacurate, but they are definitely working for the most part. (Rich has the upstream sensor voltage dropping to 2.4v while the downstream sensor reports .8v or more, lean the upstream sensor goes to 4.99 and the downstream drops to .1v)
We find bank to bank fuel trim issues from time to time, but fully expect to see both sensors on either side reporting the same condition and the fuel trim data showing that the PCM is trying to correct for it. The data seen in the fuel trims was really confusing, while it appeared to be making corrections, it was going the wrong direction according to the upstream sensors. Bank #1 was rich and fuel trim was adding fuel instead of taking it away, bank #2 was lean and the fuel trims was taking fuel away.
This truck was demonstrating a condition that proves the downstream O2 sensors have more authority than the upstream air/fuel or O2 sensors have. Combine that with bank #2 downstream sensor reporting more fuel than the upstream sensor was reporting and the only thing that makes sense is someone has cross connected the down stream sensors sometime in the past. They even secured the harnesses in place on the brackets on the transmission just like they are supposed to be making it difficult to notice visually.
We stopped in a parking lot and disconnected the downstream sensors, released the harness from the brackets and re-routed them across the top of the transmission to the opposite sides and re-connected them and then road tested again. Now the downstream sensors were on the correct sides and the system functioned correctly. The troubling part there is the shop that originally put the engine in didn't have anything to do with that part of the wiring harness that was above the transmission, they didn't cause the problem. But both they and the second shop made the same mistake, they "assumed" the that problem was related to the engine replacement instead of just troubleshooting it. By starting with that assumption in place they were blinded to all the possible causes and got trapped. Between them they each had fought this for a week, and with a disciplined approach it was diagnosed and corrected in about a half an hour.
Now for the kicker, the codes would set as pending within a few minutes of driving, and if you shut the engine down and then restarted the truck would light the MIL (check engine light) in a few minutes after that. That pending code and subsequent MIL would prevent many of the other tests the computer has to run from being performed. That means the truck could easily still have other issues that can cause the MIL to come on, but there is no way to know until the computer gets to run the tests and that of course explains why a tech can do a good repair only to have the light come back on a few days or a week later and it really is a different problem even though to a customer the light coming back on looks like "its doing the same thing".
Let's look at the other bank now. B2S1 is showing that it's lean, while B2S2 is showing that it's rich. Now unless there is a sensor or circuit issue that really doesn't make any sense.
So how could we rule out a sensor issue from the front seat of the car? A hard acceleration drives the system rich, and both upstream and downstream sensors reported the condition correctly. A closed throttle decel then results in a fuel cut-off or extremely lean and all of the sensors reported that correctly as well. So at that point one or more could still be innacurate, but they are definitely working for the most part. (Rich has the upstream sensor voltage dropping to 2.4v while the downstream sensor reports .8v or more, lean the upstream sensor goes to 4.99 and the downstream drops to .1v)
We find bank to bank fuel trim issues from time to time, but fully expect to see both sensors on either side reporting the same condition and the fuel trim data showing that the PCM is trying to correct for it. The data seen in the fuel trims was really confusing, while it appeared to be making corrections, it was going the wrong direction according to the upstream sensors. Bank #1 was rich and fuel trim was adding fuel instead of taking it away, bank #2 was lean and the fuel trims was taking fuel away.
This truck was demonstrating a condition that proves the downstream O2 sensors have more authority than the upstream air/fuel or O2 sensors have. Combine that with bank #2 downstream sensor reporting more fuel than the upstream sensor was reporting and the only thing that makes sense is someone has cross connected the down stream sensors sometime in the past. They even secured the harnesses in place on the brackets on the transmission just like they are supposed to be making it difficult to notice visually.
We stopped in a parking lot and disconnected the downstream sensors, released the harness from the brackets and re-routed them across the top of the transmission to the opposite sides and re-connected them and then road tested again. Now the downstream sensors were on the correct sides and the system functioned correctly. The troubling part there is the shop that originally put the engine in didn't have anything to do with that part of the wiring harness that was above the transmission, they didn't cause the problem. But both they and the second shop made the same mistake, they "assumed" the that problem was related to the engine replacement instead of just troubleshooting it. By starting with that assumption in place they were blinded to all the possible causes and got trapped. Between them they each had fought this for a week, and with a disciplined approach it was diagnosed and corrected in about a half an hour.
Now for the kicker, the codes would set as pending within a few minutes of driving, and if you shut the engine down and then restarted the truck would light the MIL (check engine light) in a few minutes after that. That pending code and subsequent MIL would prevent many of the other tests the computer has to run from being performed. That means the truck could easily still have other issues that can cause the MIL to come on, but there is no way to know until the computer gets to run the tests and that of course explains why a tech can do a good repair only to have the light come back on a few days or a week later and it really is a different problem even though to a customer the light coming back on looks like "its doing the same thing".
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