Need Help! - low reading on downstream 02 sensor - 07 dodge ram 1500 -

Hey everyone, I have a 2007 dodge ram 1500 with the 4.7L v8 in it. I am having an issue that I am hoping that someone with more knowledge can help me with. I recently got the code p0430 check engine light come on in my truck. The code is for inefficient catalytic converter bank 2. after talking to multiple sources and doing research, everyone said that there is a 90% chance that the converter is bad and would need to be replaced. I replaced the converter and the code came back on the same day. I furthered investigated this issue by using my scanner and looking at the voltage of the 02 sensors on both banks of my exhaust. When I did this, I noticed that my downstream sensor on bank 2 was acting weird at start up and while driving it. The downstream sensor has the same voltage as the other sensor before I start the truck, but once I start the truck the sensor loses most of its voltage within a minute or so. Sometimes the sensor with show 0.035 or so volts but nothing compared to the same sensor on bank 1 which is .685-.7 ish. When I drive the truck on the interstate the sensor will sometimes show flashes of it working......if I accelerate on the throttle it will jump up and match the bank 1 sensor 2, but then it will fall back down. The upstream sensor is working in the same fashion as the bank 1 upstream sensor so it can not be that sensor causing the issue. I figured that I have a bad 02 sensor since I am losing voltage at startup so I replaced the bank 2 sensor with a new one. I drove it on the interstate and it still did the same thing......I included a live data chart in this post to try and show what is going on....the check engine light did not come back on but it did same "pending code" on my scanner and it was the same p0430 code.....

It is now clear to me that there is a communication problem with the pigtail that connects to this sensor. There is either a problem with the computer on the truck with this sensor (which seems unlikely to me since all of the other three sensors work) or there is a problem with one of the wires going from the computer to the pigtail. It does not appear to have any cuts or burns in the wires as far as I can see.

I am not sure what I need to do next.....I do not know where/how to test the wires or see where the ground is for the pigtail. I have tried to find more information but have had no luck. I do not want to take it to the dealer and pay a lot of money to just have them look at it....they will probably assume its a bad computer and charge a lot of money to replace it..

Some help in the right direction would be great! Thanks so much!

Welcome to the forum!
I'm moving your thread to the repair section

Thank you! sorry about that

Hello jb and welcome ton the forum my first question is which side (left or right as seen from sitting in the driver's seat ) was replaced? Can you take a video of the 4 oxygen sensors and either post it hear or link it to YouTube? if so then do it with a warm engine (full operating temp)

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any exhaust leaks? also do you have a scope or multimeter to compare actual sensor voltage vs what the scanner reads?? on chryslers the o2 sensors read 5 volts with key on engine off nd before they go into closed loop. what are the fuel trims on both banks?

I will show the voltage of each sensor in a video tonight. I was told that certain brands do not work as well as others. The old sensor in the truck was a denso brand. After I replaced the converter I kept the same sensor in there which read no voltage. Then I bought a new Bosch sensor which did the same thing. I just bought an OEM Mopar sensor today and will be putting it on shortly. I do not think that the OEM sensor will solve my problem but I figured it is my last resort......if I took it to the dealer and explained my problem I am sure they will charge me a crazy amount for one. All of the three other sensors on the truck are denzo brand...

I do have a multi meter but it is a weird angle to try and test the pigtail. I will give it another shot with the multimeter. I will be posting a video in the next couple of hours with what my scanner is reading on all four sensors. Thanks!

I open the mopar packaging and turns out the oem sensor is a denso. I was not expecting that......hopefully this helps

so the new OEM Denso sensor did the same thing that the other sensors have done. I did a screen recording of what is going on. At around 2 minutes in each of the videos I give the truck some gas to get the RPMs up......the second video I tried to show the fuel trims. if any more info/video footage is needed please let me know!

Thanks for the videos! Could we also get a video with short and long term trims? Disregard those SHRTFT B1S2 and SHRTFT B2S2 - they'll never say anything but 99%.

Cheryl was asking about exhaust leaks, and I'm wondering the same. To me, the sensor is behaving like there's a genuine excess of oxygen in the exhaust, so I'm wondering where that may be coming from.

Thanks for the quick feedback! Okay sure let me take a video of that for you guys.

Sorry I forgot to answer that question.....I also read that an exhaust leak could be causing the p0430 code so that is also a possibility.....I guess I just assumed that since the sensor was not reading right and it has a new converter on it that the sensor is the last possible option......would the exhaust leak have to be around that downstream o2 sensor then? Just from a general look down there I have no seen anything but it could be so small that I wouldn't be visible....

Will be uploading the next video shortly! Thanks guys

heres the next video

here is the video of that you requested....I took it into the shop today and they said there is a small leak right behind the converter! I am having it fixed tomorrow so I am hoping that the leak will solve the problem with the sensor acting up. I'm also praying that the sensor is somehow causing that p0430 code and that there is nothing else wrong with the exhaust.....I can not see how the sensor could cause a converter inefficient code (especially since they have trouble codes for 02 sensors) but I could be completely wrong on it. I will let you guys know tomorrow if the repair solves all of my problems. I plan on getting it fixed and then taking it for a drive around town and then on the interstate

the leak hole has been fixed and the sensor is still acting up.....not sure why....im guessing it is a connection problem

That's disappointing to hear. I really hate to ask, but where did you get the replacement converter from? Because it seems to me like the catalyst just isn't storing oxygen at all, and is instead just dumping it right back into the exhaust.

If you want to prove out a connection issue, there are a couple options. One would be to use the 5V bias on the signal wire like Cheryl mentioned. The scanner won't show it due to OBDII standards, but those sensors start out at 5V cold, and get pulled down to 0-1V with heater operation. You can measure for this with DMM, and further check the O2 signal ground by shorting the signal TO the ground. If you see the bias go to zero, then you know the ground is OK.

The other would be to disconnect the PCM and load the O2 wires with some kind of light bulb, or even an incandescent test light. It's work, but it'll eliminate all doubt about the wiring. We can provide you with wiring diagrams and pin numbers if needed.

It is a flowmaster converter on it now.....I really am just guessing at this point.....

here is a freeze frame of what my scanner shows when the check engine light came on.....if someone could let me know if something is off that could lead me in another direction that would be great.....

if not, then i will start trying to test the connections and see if I can find the problem with wiring..

I see nothing off on the freeze frame, or in the fuel trim videos you posted earlier (thank you, BTW ). Really, those trims are pretty excellent, especially when the P0430 set. Nothing to suggest there's anything wrong with the feed gasses to the converter.

This video expands on the 5V bias system, if you're interested:



Also, this is the wiring diagram for both downstream O2 sensors:



I went back to the first video that you posted, with all four O2's during startup, and I gotta say... I don't see an O2 performance issue. You can tell that the B2S2 is new, as the time-to-response is noticeably faster than the other sensors.

Thanks for the advice and the diagrams!

I'm going to look into the wiring tomorrow and see if it helps my problem.