Hi folks, a question or two about O2 sensors.
I am going through a bunch of things in the backlog list on the old '04 Ram, 5.7 Hemi. While I was under the wheel wells dealing with broken manifold bolts, I could not help but notice the O2 sensors and recalling an intermittent O2 sensor code, that was popping in/out about 2 - 3 years ago actually. I cannot recall the exact code. Anyways, here's the thing ... There are no codes now and the truck just runs like a top. Smooth as silk. The only thing different from then and now is I had replaced the PCV valve on top by the firewall after which the code never ever came back.

Now, the truck has ~130,000 miles on it and the O2 sensors are original. Truck is running well, no codes, gas economy is, I think reasonable, around 18mpg, no operability issues. Was doing some reading recently where an article said the sensors can be sluggish or even toasted but the vehicle runs fine without any codes. Noticeable power and economy can be restored by replacing them. So ..... I am left wondering whether to change them out or not at the same time as I do the spark plugs and air filter. They are about 45$ each at NAPA and there are 4 of them, roughly 200$ all in. Not terribly expensive, but enough to be forced to take a pause and think about it first.
My knowledge of O2 sensors is limited. I know what they do an how they are used by the PCM. Yet know nothing about their durability or longevity wrt ongoing/preventive maintenance. Nor how to tell if they are good or bad at all.
PS: May or may not matter to know that I do run the truck with a DiabloSport i1000, with the modest 87 octane mpg booster tune installed.

Insightful thoughts and comments would be helpful and much appreciated. Thank you.

 

If they aren't causing problems, I would be real tempted to just leave them there.

Rear O2 sensors just monitor catalyst efficiency, so, if the PCM isn't whining about them, just leave 'em. Replacing the fronts *might* improve things, or not...... It's rather a crap shoot.

If you do replace them, do NOT use the Bosch sensors. These trucks just don't like 'em. NTK, or Denso please.

 

Does this help or mean anything? It looks like I can use this device (inTune1000) to select and display/record different parameters. I have no idea which ones to pick off to display and record to see what sensors are working or not.

 

Intake air temp is -64*C????? Really? I find that somewhat improbable.....

 

Well, is was -42C a few days ago, lol! Yet no, not -64. I have noticed that box, Intake air temp, has always read really cold -64C perhaps -68C once. Truck runs, and runs good, so I haven't really gone ocd on the data in the tool ... yet. But a fit is creeping up on me, I can feel it.

 

When the truck is in open loop, the PCM is going to see that COLD temp, and add fuel accordingly....... I suspect it's just a bad sensor.

 

OK thanks HeyYou.

Crawled under the truck to write down part numbers and then did a bit of online browsing today.

- Air Temp sensor has "364AA" on it. web-browsing leads me to thinking the full number is 56028364AA
- MAP sensor has 56028562AB on it. Looks like the port original had two screws through the sensor. The sensor that is there now is just a square block, no screws, 1/4 turn.
- O2 upstream 56028994AA
- O2 downstream 56028996AA

Now here is where it gets interesting, online browsing, windows shopping, reveals a HUGE variation in price for each of these. There are also multiple vendor/manufacturers of each one. Egal, Spectra, Bosch, Walker, Denso, Mopar ...... How the heck to make sense of all that and choose ones which will work but are the best price? (I have noted your caution against Bosch and been looking mainly for Denso or genuine Mopar). I will check with local Mopar on Monday, when I am siting down, in the meantime looking around.

(PS: still cannot find any leads at all on that A/C switch I busted, 2CP22-4, the autoparts in town haven't a clue and online is drawing blank pages)

 

You really want to go with mopar parts...... experience shows that the aftermarket sensors don't always play nice with the PCM, and you start getting mystery symptoms..... For simply things, like the IAT, aftermarket will probably be fine, but, the map sensor, I would go with genuine mopar.

Tried searching a few mopar parts sites, trying to find a part number for that switch, but, when searches turn up things like engine blocks, or axles (when searching the heating and ventilation section......) the results are just stupid. But, being Dodge, they may have called it a 'transducer', rather than sensor, or switch......

 

I played with the Diablo a bit today. Figured out how to pull up and display different parameters, it can livestream up to 12 on the screen.
I setup a page to display a few that should help show what is working and what is not. Based on what it was showing me wrt the IAT, MAP, and O2 sensors (rawV):
- O2 Raw have fairly quick reactions to throttle blips, it is looking like they are just fine and I will definitely leave them alone.
- IAT is frozen solid @ -64, it does not move at all. I may have to replace that. Will try some bench testing first. Am I correct in thinking: that the PCM going off O2 responses and is not looking at the IAT at all, normally. ie it is ignoring IAT most of the time.
- MAP is very responsive too, so ruling it as just fine and I will leave it alone too.
Pulled a couple of spark plugs, they are OK but are definitely due for a changeout soon. Gap is normal burnworn open up to about 0.060 now

***** ---> Anyone have link or can post the specified resistance/temperature values for the IAT sensor? I have good 4.95V supply and ground from the PCM on the plug lead. The IAT is showing me 15 to 18 kOhm at room temperature. It goes up and down a few kOhm testing with a hair dryer. So it appears to be working, however it may be operating out of range of the spec. I would need a chart or data table to verify. ... If the sensor tests as good, then that -64C has to be ruled as the scan tool looking at an incorrect data/sensor point. .... UPDATE: yeah, I went through the long menus on the tool, found other inlet air temperature parameters and selected them. Those other ones are showing active temperatures that are more in line with actuals. Therefore, IAT sensor must be just fine too.

PS: On that broken A/C switch (see "oops now what" thread). I also did some surfing today. As best I could find, it is buried in hvac parts pages, I came up with:
oem Mopar: 05073617AA = $$$$$
other aftermarket parts options: UAC 10080C, FourSeasons 20951 <-- both considerably less cost than Mopar!


Thank you to everyone for your patience and support, as I go through the process of learning about these things.