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Unread 08-05-2015, 01:25 PM   #1
Bmel17
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Check engine wrong?

I keep getting a bank 1 O2 sensor error. It was replaced and code cleared but keeps coming back every few days. Took it to a shop and it was checked out. They said everything was functioning correctly but if it keeps coming back I might need my ECM re-flashed.

Any suggestions or hints? Need to take her through inspection soon and she won't pass with that error code.

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Unread 08-05-2015, 01:45 PM   #2
JStMarie
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This is a very common issue with aftermarket O2 sensors. Most folks will tell you to buy NTK only when it comes to O2 sensors.

Never heard of re flashing the PCM for this type of problem. I'd be wary of the shops diagnosis and lean towards a less than stellar sensor.

Good Luck.
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Unread 08-05-2015, 04:46 PM   #3
Bmel17
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it's an ntk sensor. that's what had me thrown off
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Unread 08-05-2015, 07:14 PM   #4
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What code are you getting? If it's a new NTK/NGK unit you may need to check the harness for a bad connection, bare/broken wire, or bad ground.
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Unread 08-05-2015, 07:17 PM   #5
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The CEL often misleads people because the official 'cause' is not necessarily the problem. The computer simply blames the closest component. As mentioned above, start looking at harness, connections, grounding etc.
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Unread 08-05-2015, 07:26 PM   #6
jeffreyd1964
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Perhaps your cat is on it's way out?
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Unread 08-05-2015, 08:35 PM   #7
Bmel17
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Quote:
Originally Posted by jay-h View Post
The CEL often misleads people because the official 'cause' is not necessarily the problem. The computer simply blames the closest component. As mentioned above, start looking at harness, connections, grounding etc.
just had it in the shop and it was all checked out and diagnosed as fine.
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Unread 08-06-2015, 08:02 PM   #8
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To be honest I wouldn't trust a shop to say that your wiring harness is fine. I had issues with my jeep running in reverse but would turn off when I went forward. I had it brought it up to my trusted mechanic and he "checked" the wiring harness and it "seemed" fine and he wouldn't look into the problem further. My buddy and I dove into the wiring harness after buying a replacement harness from a part out here on jeep forum and turned out all of the wires running to my injectors had melted and formed into one mega wire. Go through your harness yourself from the pdc and tear open the heat shield tubing and check. If that tubing doesn't have fresh tape on it he didn't actually look at your harness.
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Unread 08-07-2015, 05:00 AM   #9
jay-h
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Quote:
Originally Posted by Bmel17 View Post
just had it in the shop and it was all checked out and diagnosed as fine.
It can be a bit more subtle than that. The diagnostic system, in most cases, does not measure the actual component, it looks for combinations of symptoms that point to the component. Unfortunately manufacturers are not always forthcoming to people other than dealers about how that works.

A few years ago I had a Subaru which kept throwing a EGR failure, even though the EGR was good. It turns out (from talking to others who faced similar issues online) that the system cannot test the EGR, so it looks for a pressure drop at about the time the EGR should kick in. Anything that fails to show that pressure drop (including the sensor that measures it) will throw an EGR failure. In my case, it eventually turned out to be a relay.

The O2 sensor failure could be caused by sensor, wiring, or maybe it's looking for matching signals from a downstream sensor which it's not getting. That's largely guesswork, though, on my part unless more info can be gathered about what the system is looking for. If anyone has FSM for that model, there may be some help there.
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Unread 08-07-2015, 07:15 AM   #10
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Another vote for going over the harness yourself carefully. Just had this experience with my XJ. Shop that I trust told me they couldn't find the problem, maybe it was PCM and that I should go to dealership. I did a little more work myself before giving up and eventually found the problem and it was the harness hidden back behind the block up against the firewall.
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Unread 08-07-2015, 08:58 AM   #11
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sounds like a stupid idea, but are you sure you are replacing the correct O2 sensor. bank 1 upstream or downstream of the mini cat ?
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Unread 08-07-2015, 10:00 AM   #12
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Quote:
Originally Posted by jeffreyd1964 View Post
Perhaps your cat is on it's way out?
X2. That's what my multiple 02 sensor CEL codes turned out to be from, it was one of the two upstream pre-cats causing the CELs. The bad pre-cat eventually came apart inside and dumped its 'innards' down into the main cat and thoroughly clogged it forcing me off to the side of the road. Installing a new header which included the pre-cats and a new main catalytic converter cured the CELs that kept erroneously indicating a bad 02 sensor.
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Unread 08-07-2015, 06:08 PM   #13
cj847
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This is one of the subjects that drives me crazy.

1) I've reviewed several hundred OBD codes - there is not a code that says "bad O2 sensor" even though at least 2 people have claimed that in this thread.
2) It is unfortunate that these are often referred to as diagnostic codes. In my mind, they are really symptom codes.

For example P132 - O2 sensor circuit high voltage. This does NOT say the O2 sensor is bad. It says the computer got a signal that it did not expect. Now you, as the "car doc" needs to investigate and diagnose.

If you go to the doctor with a bad cough, there is a 90% chance you have a cold, and 8% chance you have pneumonia, and a 2 % chance you have cancer. So he might just write you a prescription and send you away. But what he really should do is take an X ray to make sure that you don't have pneumonia or cancer.

The same goes for P 132 - there is a 90% chance that it's just a bad sensor. But it could be any of a host of other issues in your particular case.
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Unread 08-07-2015, 06:29 PM   #14
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Quote:
Originally Posted by cj847 View Post
This is one of the subjects that drives me crazy.

1) I've reviewed several hundred OBD codes - there is not a code that says "bad O2 sensor" even though at least 2 people have claimed that in this thread.
2) It is unfortunate that these are often referred to as diagnostic codes. In my mind, they are really symptom codes.

For example P132 - O2 sensor circuit high voltage. This does NOT say the O2 sensor is bad. It says the computer got a signal that it did not expect. Now you, as the "car doc" needs to investigate and diagnose.

If you go to the doctor with a bad cough, there is a 90% chance you have a cold, and 8% chance you have pneumonia, and a 2 % chance you have cancer. So he might just write you a prescription and send you away. But what he really should do is take an X ray to make sure that you don't have pneumonia or cancer.

The same goes for P 132 - there is a 90% chance that it's just a bad sensor. But it could be any of a host of other issues in your particular case.
This is the exact reason why you need to do diagnostic checks before just buying parts. I have seen many cases where a bad connection or even a vacuum leak was the cause one or more DTC's to be set. Checking the wiring and simply unplugging and reconnecting a point in the harness can correct things because that action "wipes" a contact. Best of all that type of inspection is FREE. The only cost is time.

After that, as Jerry B said, the CATs should be checked. An OBDII scan tool can look at values and see how thing are preforming which will tell even more. Another simple CAT check is to look at them after dark, are they glowing even a dull red? Do they rattle? That would indicate breakdown of the interior. It's a little more work but what do they visually look like inside?

Not all issues are as simple as a new sensor.

One tidbit, although I realize most people know this:

Bank 1 Sensor 1 is cylinders 1-3 - pre-cat
Bank 1 Sensor 2 is cylinders 1-3 post-cat
Bank 2 Sensor 1 is cylinders 4-6 pre-cat
Bank 2 Sensor 2 is cylinders 4-6 post-cat
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Unread 08-07-2015, 08:31 PM   #15
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I don't remember any OBD II code that recommends the R&R of a component?

Its a fault code that gives you an indication that something isn't operating properly, its a starting point for you to start troubleshooting using your skills to understand and identify why the code is being set.

Without the OBD II system you'd be spending a lot more money at a shop for fixing your TJ... IMO
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