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Discussion Starter · #1 ·
The Check Engine light lit up on my son's '96 Ram (5.2L engine) and when I had the code read at AutoZone it pointed to the pre-cat "upstream" o2 sensor. I'm sorry, i don't remember the code. I bought two new sensors (Denso, only because the price was right) and replaced them.

The tip I want to pass along relates to removal of the old sensors. I rented the oxygen sensor tool from Advance Auto, and it worked well enough for the rear (downstream) sensor, but the front (upstream) sensor wouldn't budge, even after shots of PB Blaster and some time spent waiting for it to work. I ended up destroying the sensor that I was trying to remove, which ended up being a very good thing because it allowed me to slip a 7/8 box-end wrench over the sensor and thanks to the wrench's long handle (and with some help of the PB Blaster I'm sure), the sensor came right out. The next time I go to remove an o2 sensor, if I'm 100% certain I'm going to replace the sensor, if I can't get the sensor to budge I'm going to cut its wires and use a long handled box-end wrench.

By the way, the Check Engine light went out after a couple of drive cycles, once the sensors were replaced. I love it when that happens.

For our '96, the Denso part numbers for the sensors are 234-4077 and 234-4079. The sensors are easy to find. One is just upstream of the catalytic converter, and the other is in the tailpipe downstream from the cat. Both have in-line electrical connectors that are easy to find, just follow the wire away from the sensor until you find them. Lift the connector's tab gently, and the connector should slide apart with a little effort. They're connected to the truck frame via plastic tabs that you just push into the hole. I can take some pictures and post them here if anyone would like to see them.
 

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I need to change them too. But when I call to ask the prices, they tell me that I need to know the length of the sensor's cable. Just want to be sure which ones I have to buy to avoid surprises.
Mine is a 98 5.2L with probably factory ones.
And other thing is, it only has two, right? Because I called autozone and they asked me if I have to change the 4 :4-dontknow:
Thanks!
 

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Another tip warm the pipes a bit not to hot. Drive the truck a bit then hit it with penitrating oil let it sit. Then take out sensor when its warm to the touch.
 

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I agree with you, Ramfan, excet I don't let 'er cool off, always worked for me, and I don't use any lube, tho it couldn't hurt, a 1/2 impact set to rattle gently, and turn up the air until it unscrews has been pretty successful. I made my socket with an impact socket, I think its a 22mm, but I'm probably wrong
 

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Discussion Starter · #6 · (Edited)
I need to change them too. But when I call to ask the prices, they tell me that I need to know the length of the sensor's cable. Just want to be sure which ones I have to buy to avoid surprises.
Mine is a 98 5.2L with probably factory ones.
And other thing is, it only has two, right? Because I called autozone and they asked me if I have to change the 4 :4-dontknow:
Thanks!
The question of wire "pigtail" length caused me some confusion, too. I finally decided to get under the truck and have a look. There are two sensors on our truck. The upstream sensor just needs the 12" pigtail and the downstream sensor needs the 18" pigtail. Before buying anything, though, I'd have a look under the truck to make sure.

Here are some cross-references I came up with. Again, double-check for your application before buying anything.

Denso:
Upstream: 234-4077
Downstream: 234-4079

Delphi:
Upstream: ES20044
Downstream: ES20046

Bosch:
Upstream: 15705
Downstream: 13280

I plan to take some pictures this weekend and post them here.

Don't forget to put a little bit of anti-seize compound on the new sensors' threads before you install them. This should be included with the sensors when you buy them.
 

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Thank you very much, DadzDodge.

I'll try to have a look before buying anything.
Is it easy to see without lifting the truck?
 

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Discussion Starter · #8 ·
Thank you very much, DadzDodge.

I'll try to have a look before buying anything.
Is it easy to see without lifting the truck?
Yes, sort of. I have an L-shaped driveway and I park the center of the truck over the grass while leaving the wheels on the asphalt. This allows me a way to get under the truck without raising it up. (I do still chock the wheels). If you have a way to get under the truck safely, you'll quickly find the sensors right within reach. The electrical connectors are easy to reach, too. It'll probably be Sunday afternoon before I can get to it, but I'll definitely post up some pictures to walk you through the process.
 

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I get down the truck a while ago, located the two sensors (good thing only has two). I saw the one before the cat has longer cable than the one after it. I thought that the upstream had 12" and the downstream the 18", or maybe someone changed them and put what they wanted.
Does it make any sense?
 

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I don't understand why you didn't use a box end wrench from the beginning? You can just unplug the harness and slip the wrench over the wires (in most cases). The only thing I can think of is the harness plug was too big to do so? Even so, I've never gotten stuck on them even with an open end wrench. I also drive the truck or at least let it idle until the exhaust is warm, that way the sensor will release easier.

Also, the downstream sensor did not need replacing, and even if it did, it's not really necessary as all it does is monitor catalytic efficiency. But either way you got your problem solved :).
 

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Discussion Starter · #11 ·
Joe1500 -- I checked several suppliers' web pages before being convinced I only needed a 12" pigtail on the upstream sensor. I finally got under the truck before placing the order, just to be sure. Everything worked out fine, and the 12" pigtail for the upstream sensor and the 18" pigtail for the downstream sensor were both just right for our truck. I think where the confusion comes from is some trucks have two upstream sensors, one on either side of the truck, and one requires a longer pigtail than the other. At least that's the conclusion I arrived at. Also, yes, it's very possible that someone has already changed your sensors once. On our truck, there was an NTK sensor on the front and a Bosch on the back. Given that the downstream one came out easily, I suspect it had been replaced sometime in the past.

Snrusnak - the 7/8 box end is too small to fit over the electrical connector. Also, the oxygen sensor tool I was using was starting to round off the sensor's corners, so I was very happy that the sensor broke allowing me to fit the 7/8 box-end over the sensor's base. I had already warmed the exhaust AND used PB Blaster (and let it soak for a bit) but that sensor wasn't going to give up without a fight!

You're right, I didn't have to swap out the downstream sensor but the sensor wasn't expensive so I thought it would be a good idea to go ahead and swap it out while I was under there.
 

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Discussion Starter · #12 · (Edited)


This picture is looking towards the front of the truck, and you can easily see the downstream sensor on the right side of the picture (very close to the camera). Follow its wiring to an in-line plug which is attached to the truck using a plastic push-in plug on the lower side of the transmission.

The upstream sensor can be seen in this picture as well. Look for the catalytic converter, which is oval and mounted vertically, then in the shadows you can see the upstream sensor. It's pointed towards the 10 o'clock direction, and its electrical plug is up high, mounted to the truck using the same kind of plastic, push-in plug mounted above the transmission.



This picture was taken from about the same location, but I tried to get a little closer so you can see the location of the electrical connectors. The downstream sensor plugs in down low, and the upstream sensor plugs in up high. The part numbers shown in my earlier post are for sensors with a 12" pigtail (upstream) and an 18" pigtail (downstream). As you can see, this worked very well, with sufficient slack but not so much as to allow the wires to hang down and be damaged.



This picture may be helpful in that it shows the exact location of the upstream sensor, which as you can see is mounted right at the input to the catalytic converter. Note how its located just aft of the pipes bringing the exhaust from the left and right manifolds.

I hope these pictures help -- if anyone has any questions, of course post 'em up and I'll help however I can.
 

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Can I ask you where you got them? My engine check light come on and disappear every once in a while and I know it's the O2 sensors so I am thinking about replacing them too.

Thanks
 

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I take that these pictures and instructions (7/8 boxed wrench, etc...) would more or less be identical for the 5.9 as well? Obviously different O2 sensor part numbers though?
 

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Discussion Starter · #17 ·
Yes, I would think so. Some configurations have an additional upstream sensor but beyond that, I would think everything else is the same as long as you have room to swing the wrench. (I replaced the sensors on my wife's van some time ago and there's no way I could have put a wrench on one of the sensors because of its location, so it all depends).
 

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Thanks for the part numbers and the pics. Took my truck to Auto Zone to get it scanned and came up with o2 sensor bad ( bank 1 sensor 1 ) and they wanted $70 plus tax for it. Was able to use these part numbers to find it online from Amazon ( have Amazon Prime membership ) for $30 including overnight shipping :SHOCKED: So that will be part of my Saturday project!
 
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