Why are my O2 sensors disconnected, No CEL - JeepForum.com
 
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post #1 of 13 Old 09-18-2017, 07:18 AM Thread Starter
navipro
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Why are my O2 sensors disconnected, No CEL

Hi Guys, so yesterday I was getting ready for the clutch job on my 2000 TJ 4.0. Why under the jeep I have noticed that the wires that go to O2 sensors (I assume they are O2 sensors) just after the headers are cut. Also I could not find where the sensors get plugged into.
There is another sensor downstream (after the pipes are connected and before catalytic converter). And that wire seems to be intact. Also there is a sensor in cat and it seems to be ok.
This jeep is new to me and PO had it for 7 years. I have asking him about it and he said he did not know about it.
What is also strange is that Jeep passed the emissions testing last week and there is no CEL. I am not sure if it was disconnected. I will have to buy an OBD2 reader to get the codes.
I have found few disconnected plugs under the hood. Can you guys help me identify them? I will post pictures in the next post

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post #2 of 13 Old 09-18-2017, 07:32 AM Thread Starter
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So,
Pic 1 - Cut wires on the sensors
Pic 2 - Sensor downstream before cat
Pic 3 - 2 plugs under the hood. Do you know what they are?
Pic 4 - Another mystery plug
Pic 5 - This looks like some sort of fill hose. It is capped. Looks like it is going to transmission......
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post #3 of 13 Old 09-18-2017, 07:33 AM Thread Starter
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post #4 of 13 Old 09-18-2017, 08:43 AM
NotURMailman
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The open plugs probably should be going to the O2 sensors.
The wire leads that are cut off are pretty long.
The "hose" you're talking about is probably the transmission vent line.
Sorry, but I can't see the pics on my work computer so I had to look on my phone, which makes them small and hard to see...


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post #5 of 13 Old 09-18-2017, 01:29 PM Thread Starter
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Originally Posted by NotURMailman View Post
The open plugs probably should be going to the O2 sensors.
The wire leads that are cut off are pretty long.
The "hose" you're talking about is probably the transmission vent line.
Sorry, but I can't see the pics on my work computer so I had to look on my phone, which makes them small and hard to see...
That's what I thought at first too, but the plugs have 2 wires and sensors have 3.......
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post #6 of 13 Old 09-18-2017, 07:11 PM
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Quote:
Originally Posted by navipro
That's what I thought at first too, but the plugs have 2 wires and sensors have 3.......
The 2 connectors under the hood look like the leak detection pump and cruise servo.
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post #7 of 13 Old 09-18-2017, 07:40 PM
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Is your TJ a 49 state?
Does the exhaust system have mini cats?...
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post #8 of 13 Old 09-19-2017, 01:35 PM
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I'm thinking what knucklehead is thinking. Looks like a two piece exhaust manifold was put on a early 49 state jeep without the extra O2 sensors.
The plugs you show are not O2 sensor plugs. Could be A/C if you don't have it. The tube is your transmission vent so no worries there, although it should have that metal tab mounted to a bell-housing bolt. Sometimes people relocate them higher to try and keep water out longer, but it should be mounted somewhere not just dangling.

I would bet your jeep only came with a single upstream and single down stream O2 sensor and the two that are cut off are just plugging the holes for the extra two. So long as your two are hooked up, and I'm pretty sure one of them is circled with the transmission vent, you're good to go.


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post #9 of 13 Old 09-19-2017, 01:39 PM
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Actually you have coil on plug ignition too instead of cap and wires. I thought 2001 was the first year for that. Could be an engine swap which might explain the detached trans tube, the 50 state O2 sensors and the newer ignition. I could be off on the switchover year though. Either way I bet someone had the jeep apart before.


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post #10 of 13 Old 09-19-2017, 04:57 PM
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The only year TJ's that have 49 state and 50 state exhaust emissions is the 2000 4.0L.
The 49 state (non California) has one O2 sensor just before the single catalytic converter next to the transfer case/transmission and one installed in the rear, side of the converter. A total of two O2 sensors.
The 50 state qualifies to meet all 50 state requirements for emission's.
All 2000 4.0L engines have the coil on plug rail and the 2 piece exhaust manifold. The 49 state comes from DC with plugs in place of O2 sensors on the exhaust manifolds...
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post #11 of 13 Old 09-20-2017, 11:11 AM Thread Starter
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Thanks guys, I think you are onto something. I have noticed the yellow numbers painted on the block and on the front of the engine, similarly to what they do at junk yards. It is strange that p.o. did not mention it, as he had if for the last 7 years. Maybe it was done before him.
Btw, I am in Canada, but I do not think that we have requirements similar to Calif.

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post #12 of 13 Old 09-20-2017, 08:49 PM
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Now how about filling in your profile so that its easier to help you?...
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post #13 of 13 Old 09-21-2017, 07:11 AM Thread Starter
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Originally Posted by Knuckelhead View Post
Now how about filling in your profile so that its easier to help you?...
Yes, you are right. Should have done this in the first place.
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