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.
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.