Which scan tool for testing O2 sensor?

[Jimmy9190]

This is about my 2001 Dodge Dakota pickup truck. It has a 3.9 liter V6, 5 speed manual, just shy of 162,000 miles on it now. This morning the CEL came on, and with my truck I can do the "key dance" to display DTC's in the odometer. It is showing P0432 which is for the right exhaust catalytic convertor being at half of its specified efficiency.

I am at work but was able to do a little research on it, and it could be the downstream O2 sensor causing the problem. I replaced the upstream O2's about 60,000 miles ago, used NTK parts. The downstream O2's are still the orignal Mopars. I need a good scan tool to test the operation of the O2's but I am confused on which one to buy. I do not need nor can I afford a pro-grade Mac, Matco, Snap-On or other pro tool. Actron or HF is more in my budget but I don't know much about the scanners to pick the best one for checking O2's.

I appreciate any help/suggestions on this. I need to rule out the O2's before I replace the cat. I would much rather just replace the O2's. Thanks.

 

[michaelluscher]

Do you have access to some sort of Android device? As long as it has Bluetooth and is relatively new, the $5 Torque app should give you all you need.
A $24 BAFX OBD2 reader on Amazon should complete the deal.

 

[ARCOgraphite]

No safety or smog inspection in FL right?

Bye bye cats!

OTW sound cheaper to "just" replace the rear sensor. Are there 2?
Really, I would think all that stuff would be toast at these miles.

Good luck. Sounds like a fun truck.

 

[Cardenio327]

Switch the two downstream sensors from side to side and clear the codes. If the code comes back for the same side it is the catalytic converter or the wiring, if it comes on for the other side it is the O2 sensor.

 

[Sawdusted]

If you want to look at voltages for an o2 sensor, you'll need one which can handle live or real time data. If the ECM is reporting voltages not within the specified range, I would test the voltage directly at the o2 sensor itself. Note that you will need a fairly good DVOM to handle the fast switching voltages.

I have alo seen a case where the o2 sensor is working fine but the ECM is not processing the voltages correctly. So the ECM could also cause a o2 sensor fault when the o2 sensor is working fine.

At your vehicle' sage. It is likely the o2 sensor is gone. My 2 cents. Just saying.

 

[Jimmy9190]

Thanks for the help guys. I agree it probably is the O2 because there is no rotten egg smell or gasoline smell from the exhaust, no fumes like in an exhaust leak, and my truck routinely gets about 19 MPG which is very good for a Dakota. I track my MPG on fuelly.com every time I buy gas. I would think if the cat was bad the MPG would be the first thing to have a problem. My truck actually runs great for its age. I have kept it in very good shape.

Back when I replaced the upstream O2's I did not replace the downstream O2's because they are said to "not really do anything" and it is best to leave them alone until they have a problem. 162K is probably a very long life span for an OEM sensor. I will need to do some online shopping for a good scanner and NTK O2's when I get home today.

 

[The_Jeff]

This is one of those times where the scanner will show you numbers jumping all over the place, as fast as it updates, but you won't really know if it's what the programming requires.

I like the idea of changing rear o2s to see if it follows.

 

[Wolf359]

Originally Posted By: Jimmy9190
Thanks for the help guys. I agree it probably is the O2 because there is no rotten egg smell or gasoline smell from the exhaust, no fumes like in an exhaust leak, and my truck routinely gets about 19 MPG which is very good for a Dakota. I track my MPG on fuelly.com every time I buy gas. I would think if the cat was bad the MPG would be the first thing to have a problem. My truck actually runs great for its age. I have kept it in very good shape.

Back when I replaced the upstream O2's I did not replace the downstream O2's because they are said to "not really do anything" and it is best to leave them alone until they have a problem. 162K is probably a very long life span for an OEM sensor. I will need to do some online shopping for a good scanner and NTK O2's when I get home today.


That's what everyone says about the downstream ones. They say all they really do is tell you if your cats are bad. I'm at 186k on original downstream sensors on a different car, I did replace upstream at about 175k. Also as for scanner, that BAFX mentioned earlier is probably one of the best, there are cheaper ones at $10-$15, but sometimes they work sometimes not. It's what I got and works fine with Android or even Apple products. I think it also works with laptops that have bluetooth too. The dedicated code readers are more limited and more money.

 

[Jimmy9190]

Everything I read here and elsewhere online says the cat may very well be OK and the downstream O2 sensor could be the problem. Before I left work today I slid under my truck and smacked both cats with my fist. I also smacked them with a rubber mallet when I got home and did not hear any rattles or noises either time. The exhaust does have a slightly sweet/rich smell to it, but only when I got right up near the tail pipe and got a good whiff. Other than that there are no odd smells or fumes that I can detect.

I guess O2's can fail more often than cats do, but regardless I am going to replace both downstream O2's first. I bought two new NTK O2's from AAP tonight, paid online, did two separate transactions, each with a different $30.00 discount code and saved $60.00 on both parts. NTK is the supplier for OEM Dodge and my total cost was about $112.00 with tax.

I will install the new O2's tomorrow after work and see how it goes after that. I will leave the CEL on and not reset the PCM and see if the code clears on its own. Then I should know for sure whether the O2 is/was the cause of the problem. My original Mopar O2's are both very old now and need replacing anyway.

Right now I don't see a need to buy a scanner or code reader. From what I have learned about them here I probably would not be able to interpret the info from the scanner anyway. If I need to I can ask the guys at AAP to clear my CEL code.

Thanks very much for everyone's help and info on this.

 

[Wolf359]

Originally Posted By: Jimmy9190
Everything I read here and elsewhere online says the cat may very well be OK and the downstream O2 sensor could be the problem. Before I left work today I slid under my truck and smacked both cats with my fist. I also smacked them with a rubber mallet when I got home and did not hear any rattles or noises either time. The exhaust does have a slightly sweet/rich smell to it, but only when I got right up near the tail pipe and got a good whiff. Other than that there are no odd smells or fumes that I can detect.

I guess O2's can fail more often than cats do, but regardless I am going to replace both downstream O2's first. I bought two new NTK O2's from AAP tonight, paid online, did two separate transactions, each with a different $30.00 discount code and saved $60.00 on both parts. NTK is the supplier for OEM Dodge and my total cost was about $112.00 with tax.

I will install the new O2's tomorrow after work and see how it goes after that. I will leave the CEL on and not reset the PCM and see if the code clears on its own. Then I should know for sure whether the O2 is/was the cause of the problem. My original Mopar O2's are both very old now and need replacing anyway.

Right now I don't see a need to buy a scanner or code reader. From what I have learned about them here I probably would not be able to interpret the info from the scanner anyway. If I need to I can ask the guys at AAP to clear my CEL code.

Thanks very much for everyone's help and info on this.


Just for completeness, they're about $38.79 each on rockauto, but as you can't wait for shipping, getting them at AAP makes sense, but as you can see, even with their discount codes, it can still be cheaper online. There are even generic ones you can get that are only about $22 each.

 

[Jimmy9190]

I checked Rock, even had the parts in the shopping cart but decided not to wait for shipping. They would not have arrived until Monday or Tuesday and I do not want to drive my truck that long with a possible bad O2 or cat. Shipping from Rock was $10.00 so each NTK would have cost about $44.00. With the $30.00 discount at AAP they cost me $55.00 each. The $22.00 difference is worth it to me to be able to replace the O2's now. I have found that the cheaper generic O2's and Bosch O2's sold at parts stores do not work well at all in Dodges. It is all over the Dodge forum, OEM or NTK/NGK is the only O2 that works correctly with the Magnum engines, and the generic and Bosch O2's are even worse when used with the Hemi's.

Back when I was working from home and did not drive nearly as much I had the luxury of waiting for shipping, but I need the truck for work now plus I will need it this weekend to pick up a few things at Home Depot. I just hope these new O2's solve the problem and I don't need a new cat.

 

[ARCOgraphite]

I don't understand why you would put money into this - the post cat sensor does not adjust mixture and does not affect emissions. If A cat deteriorates on a older high mileage vehicle, Id just "gut" it.
Again, I know Lee county does not inspect for smog or safety - does your county?

 

[Jimmy9190]

I live in Lake County, there is no emissions testing here right now but you never know what the county gov't might come up with next. I hope these new O2's will fix the CEL and I don't have to do anything with either one of my cats. On my truck the PCM compares input from the upstream and downstream O2's for each cat to determine whether the cat is working within specs. If the downstream O2 is dead it may cause the PCM to think the cat is not at capacity and throw a code for the cat when really the O2 is at fault. 160K is a very long time and a lot of wear on an OEM O2 sensor. I do not have any of the obvious physical signs of cat failure, so I would really just like to be able to simply replace the O2's and let that be the end of it. If the cat is bad I will replace it, because I want to keep the truck the same as it has been all along.

 

[Jimmy9190]

Well it's not the O2 sensor. I replaced both O2's tonight and went ahead and cleared the code because I was anxious to see whether it would come back. I bought one of the cheap Actron code reader-eraser tools at AAP tonight to clear the code. Everything went fine with R&R'ing the O2's and I went for a test drive, only went about 3 miles and the CEL came back on while I was stopped at a red light. It's the same code, P0432 so the problem has to be the cat. If anyone has any ideas or tips I am all ears. I need to fix this problem as soon as I can but I need to learn more about it first.

 

[buck91]

I used elmscan5 with obdwiz on my laptop to check the o2 sensors on my 99 F250. It wont read them on my 2011 though...

 

[zzyzzx]

I don't trust O2 sensors past 100K. Just get a new Bosch one and be done with it. Or use a spacer on the rear O2 sensor.

 

[Donald]

Assuming you bought quality O2 sensors and they are properly connected what else could it be besides a bad cat?

Some states are getting anal about cats. I think NY and CA need a different cat than the other states.

I do not believe driving around with a bad cat for awhile would hurt.

 

[Jimmy9190]

Originally Posted By: Donald
Assuming you bought quality O2 sensors and they are properly connected what else could it be besides a bad cat?

Some states are getting anal about cats. I think NY and CA need a different cat than the other states.

I do not believe driving around with a bad cat for awhile would hurt.


Thanks for the help. All 4 O2's are NTK, which is the supplier for Mopar OEM O2 sensors. The upstream O2's have about 60,000 miles on them now, I just replaced both downstream O2's last week. I still have the code and I need to do more tests and research before I buy a new cat/exhaust pipe assembly. Truck is running fine but I want to fix it before it gets worse.

 

[Donald]

The code says your cat is not performing up to snuff. I would assume the downstream O2 sensor is the only thing that could detect that?

 

[yonyon]

Originally Posted By: Jimmy9190
Well it's not the O2 sensor. I replaced both O2's tonight and went ahead and cleared the code because I was anxious to see whether it would come back.


Downstream O2 sensors don't fail in such a way as to set a cat efficiency code. I've been unscrewing sensor since 30 years before I was even born and never once have I seen replacing a downstream O2 sensor make a cat code go away. This is what you do :
1- check that the front O2 sensors are working properly
2- check for any applicable PCM software updates
3- drive the car until coolant temperature stabilizes + 2 minutes, note any drivability problems
4- stop and note the fuel trims, both long and short for the appropriate bank

If there was any sort of engine performance problem, resolve that first. If it drove fine and the light came back on while the fuel trims were all within +-7 you blame the cat. If the fuel trims went wild, fix whatever's causing that problem. If the light stayed off, try driving it again.