Disconnected upstream O2 sensor but no change

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Krischick33

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May 10, 2020
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2001 2.5l, 5sp, 108k miles

Question. I just disconnected my bank 1 02 sensor.
I wanted to see if it would change a rough idle on cold start and a thought that I'm running rich.
There was no change at all. Same rough idle.
It did trigger a couple fault codes...P0132 and pending P0135.

What does this prove? Anything?
 
The O2 sensors are not used until the coolant is up to operating temp.

So, no change would be expected on a cold start.

Check your coolant and air temp sensors as they are used at startup.
 
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Ok. I changed the coolant temp sensor recently. Didn't know about the air intake sensor. I'll get one and see if that makes a difference. Tx.
I'll update tonight.
 
I didn't get a chance to pick up the air intake sensor last night. Before I throw another $30 at this issue. Data from Torque Pro shows intake temp of 61° and coolant temp of 183°. This is during a 30 minute highway drive...30° outside temp. Does this seem correct? Could my thermostat be stuck open.
 
I have no experience with the 2.5, but assuming it runs the same 195 deg thermostat as the 4.0, the temp sensor on a 4.0 will read around 210 deg fully warmed up.

You can check the air temp sensor when the engine is cold. Simply check it to see if it matches the outside temp. Coolant temp sensor as well.
 
Would there be a chance my 2000 model didn't come with 4 O2 sensors?
Or maybe the PO removed some?
I got a code "bank 1 sensor 1"
For the life of me, I can't find it. I've seen all the diagrams so I know that I have been looking at the right locations.
 
Not trying to be a smart a**, but if your looking at the parts assembly for your engine/exhaust system and it shows 4, then you probably have 4.

I will say that up until I believe ‘02, the 4.0l had only 2, and the exhaust manifold was all one piece and a single discharge port. After that, they split the manifold into two, each exhausting 3 cylinders. There are 4 O2 sensors on those engines.
 
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No, I was just looking at the diagram on this forum.
After doing a little more digging, I may only have the two.
What caused all this is my check engine light came on and I stopped by the local auto parts store and he said the code read Bank 1 Sensor 1. (Sorry I didn't get the code #). So on my way home I filled up with premium fuel and poured in a can of seafoam.
Light went off after a few miles.
Kind of in a quandary.
 
Sea foam is pretty darn good stuff in my opinion.

Don’t always assume the issue is the O2 sensor - it would be of great benefit for you to get a OBDII Bluetooth dongle for your Jeep, and the associated app for your phone. Then you can get a better idea of what’s going on with your engine.

This guy does a decent job of explaining the importance of knowing what the engine is doing before throwing parts at it to fix it - particularly as relates to the O2 sensors -

 
Roadhand01 said:
No, I was just looking at the diagram on this forum.
After doing a little more digging, I may only have the two.
What caused all this is my check engine light came on and I stopped by the local auto parts store and he said the code read Bank 1 Sensor 1. (Sorry I didn't get the code #). So on my way home I filled up with premium fuel and poured in a can of seafoam.
Light went off after a few miles.
Kind of in a quandary.
Click to expand...
Higher octane gas will never (!) fix or help problems like that. First, all octane levels in the US have more than enough cleaning additives to keep the fuel system clean. The EPA even mandated that back in the 80's since fuel injected engines became the norm. Second, higher octane fuels are actually harder to ignite, the additional octane's purpose solely to make the fuel less likely to self-ignite due to compression in high compression/high performance engines. If it's not a high compression engine, and our Jeep engines are not, additional octane does nothing except help to drain our bank accounts slightly faster.

And as above, O2 sensors aren't used by the computer when the engine is still cold. The engine has to have started to warm up before the computer starts to use the O2 sensor(s) to set the fuel mixture. When the engine is cold the computer uses a pre-programmed table of values to set the fuel mixture with.

If your engine only runs roughly when cold I'd suspect an incorrect temperature problem, like a defective intake air temperature sender. If your temperature gauge on the instrument cluster isn't reading properly, its temperature sender adjacent to the thermostat housing might be bad.
 
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Jerry Bransford said:
Higher octane gas will never (!) fix or help problems like that. First, all octane levels in the US have more than enough cleaning additives to keep the fuel system clean. The EPA even mandated that back in the 80's since fuel injected engines became the norm. Second, higher octane fuels are actually harder to ignite, the additional octane's purpose solely to make the fuel less likely to self-ignite due to compression in high compression/high performance engines. If it's not a high compression engine, and our Jeep engines are not, additional octane does nothing except help to drain our bank accounts slightly faster.

And as above, O2 sensors aren't used by the computer when the engine is still cold. The engine has to have started to warm up before the computer starts to use the O2 sensor(s) to set the fuel mixture. When the engine is cold the computer uses a pre-programmed table of values to set the fuel mixture with.

If your engine only runs roughly when cold I'd suspect an incorrect temperature problem, like a defective intake air temperature sender. If your temperature gauge on the instrument cluster isn't reading properly, its temperature sender adjacent to the thermostat housing might be bad.
Click to expand...
All good information.
No problem with it running rough. It runs very good. Temperature runs normal.
The check engine light just came on and I was trying to figure out about the bank 1 sensor 1 as mine doesn't seem to have.
I believe it is the one piece manifold that MrMark 52 referred to. Sorry for not having more knowledge on this but 1st time jeep owner. The main reason I joined this forum was because of the invaluable information.
I have ordered a OBDII Bluetooth dongle so maybe I will learn something.
 
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Look at the driver's side of your engine from the top, do you see two cylindrical shaped cannisters maybe 5" in diameter just below the exhaust headers? If you do, those are pre-catalytic converters meaning you have four O2 sensors, bank 1 upstream & downstream, and bank 2 upstream and downstream. Your 2000 TJ is a transition year, early models only have one catalytic converter located under the Jeep. Later versions and 2001 and newer have 3 catalytic converters... 2 pre-cats as described with one more underneath the Jeep.
 
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Another way to tell is get under your Jeep and follow the exhaust pipe to the engine, starting a the belly plate under the transmission. As you move toward the engine, the pipe will lead under the passenger side of the engine to near the front of the engine, then turn under the oil pan, then turn toward the rear of the vehicle.
At the point that it turns up - if you have 4 O2’s, the pipe will split to 2 pipes (below the coffee canister like pre-cats MrBlaine spoke of).
It takes a weird viewing angle from the top of the engine to see the pre-cats. But the cats themselves are shrouded with a heat deflector. You’ll be able to see a gap between the precat and the shroud.

They look like this (precats as found on later models as per MrBlaine) and are positioned together as seen in this picture. You can see an O2 sensor in the upper left corner of the picture. Both downstream O2 sensors are rust after these cats, while the upstream is on the exhaust manifold.
Per the parts manual I have, your Jeep will not have these - It will only have a single pipe going up and attaching to the exhaust manifold (the parts book I’ve got doesn’t show where the O2 sensors are located).

1608577748666.jpeg
 
Wait! In you original posting you said you had a 2.5l - my memory is failing me as I age, but that sure looks to me like a 6 cylinder 4.0l.

See also the diagram below which came from the JeepOverstock.com website and shows both the 2.5l and 4.0l exhaust systems. (FWIW - my ‘03 4.0l is similar to the engine assembly shown on the right except that first assembly flange after the precats is not there).

From your picture, l’m guessing you have some mutation. I can see what appears to be an exhaust pipe coming in horizontally from (with respect to the picture) top - that doesn’t make sense.

Maybe a picture from the wheel well side would help. I also just looked at the BOM for your year Jeep - it shows the 4 cylinder intake manifold, but doesn’t show the exhaust manifold. It also shows only a single exhaust header as the picture below for a 4 cylinder.

Again, maybe you have a mutation 😀

1608647793537.jpeg
 
Well I sure have learned something today. The pre-cats have been removed with the O2 sensor bungs capped.
Thanks dla for posting those pictures. I was thinking it almost time for the retirement home.
Sensor 1 Bank 1 code is what started all this.
 
MrMark52 said:
Wait! In you original posting you said you had a 2.5l - my memory is failing me as I age, but that sure looks to me like a 6 cylinder 4.0l.

See also the diagram below which came from the JeepOverstock.com website and shows both the 2.5l and 4.0l exhaust systems. (FWIW - my ‘03 4.0l is similar to the engine assembly shown on the right except that first assembly flange after the precats is not there).

From your picture, l’m guessing you have some mutation. I can see what appears to be an exhaust pipe coming in horizontally from (with respect to the picture) top - that doesn’t make sense.

Maybe a picture from the wheel well side would help. I also just looked at the BOM for your year Jeep - it shows the 4 cylinder intake manifold, but doesn’t show the exhaust manifold. It also shows only a single exhaust header as the picture below for a 4 cylinder.

Again, maybe you have a mutation 😀

View attachment 212312
Click to expand...
Krischick33 made the 1st post. I believe his is the 2.5
 
Roadhand01 said:
Krischick33 made the 1st post. I believe his is the 2.5
Click to expand...
Grrrrrrr - frustrating when people tag onto a thread with a totally different engine than what the OP posted about. This thread started out talking about a 2.5l, and got switched to a 4.0l. I guess in most cases it doesn’t really matter but in this one, it does.
 
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@Roadhand01 - With those 2 sensors removed, you should be seeing more codes than for S1B1.

Is this a new to you Jeep?

Someone went to a lot of trouble to remove the precats because that piping all looks factory to me.

Go to the technical section of the forum and get both the Parts Manual and Factory Service Manual for your year model. See if your year model may have come from the factory this way. If it didn’t (and the 2.5l’s didn’t have precats that I’ve found), then your S1B1 may be on a welded in bung just after the header collector. Usually on the upper half of the pipe so as not to get scrapped off by road obstructions or rocks (when rock climbing).

Bottom line, without the required O2 sensors, the Jeep would always have a CEL.
 
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