Hi all! I have a 2004 Hyundai Elantra that is having problems getting the Cat test to go complete. It is stuck as incomplete and has a pending P0420 code. The code has been pending for the past two weeks, maybe longer as that’s when I first started checking because I wanted to get inspected. This is my first car so I’ve only owned it for a year, I have no idea if the O2 sensors have ever been replaced. I bought a “more fancy” scan tool than what I was borrowing from my dad (OBD Scan tool from the early 2000s to a cheap phone one since I’m going to college soon.) I used the new tool to graph the O2 sensor data and would like some opinions on it. Do you guys think it’s a lazy upstream O2 sensor or could it actually be the Cat? The O2 sensor and heater monitors both show ok but something just seems off. Thanks in advance!
If the upstream O2 sensor is lazy but still (sort of) working, how come the car is able to enter a closed loop? That’s my only concern with my hypothesis with the O2 sensor being bad.
Oh okay, that explains the fuel system loop question. I thought that O2S1 was upstream and O2S2 were downstream, since they’re both bank 1 if I’m reading it right.
So you’re leaning towards it being the O2 Sensor if I’m correct? Do you think it’s the O2S1 sensor like I was alluding to above? I don’t have any driveability issues, just the CAT monitor staying at incomplete with the code staying at pending, it won’t go away or set permanently. If I erase it it just comes back, same deal.
Don’t look like you had a hot enough engine when the graph was captured. Sensors don’t work or work correctly until the exhaust is at around 640 degrees.
According to this, I would change the downstream sensor. $30 if you do it yourself.
OP has no other symptoms than an error code. True, it could be a going bad cat, but there have been no tests performed to determine that. I.e. bad acceleration, funny exhaust smell, running hot, performance issues, etc.
That’s why I recommended to simply switch the sensor around. That can be one way to determine a bad sensor. A bad sensor can give unpredictable values and that is how people replace cats that are perfectly fine only to find out later that cause is something other.
The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle.
I think we both said the same @Tester and we don’t know if any of that is happening. With the limited info provided it make me crinch when I read suggestions that appear to be definite and final.
Hello everyone! The readings were in fact not from too hot of an exhaust. I’ll drive around tomorrow and take some readings at the very end at idle after driving around for a while. I like the idea of switching both O2 sensors around to see how they react. I’ll do that as soon as I have time, sometime this week. I’ll upload more graphs tomorrow after driving and getting data on the sensor when everything is very warm. The car has 108,000 miles. I got it last year with about 102.3k on it, I have no idea when or if the O2 sensors have ever been replaced, as that would’ve been before I bought it. I just want to re-iterate, the code is only pending, the MIL has never turned on for it. Just so everyone knows, it does light during startup, so the light does work. It’s stayed as pending for the last 2 or more weeks, I just notice because I need to get inspected. Thanks for all the info so far everyone!
Okay, I’ll make sure that both sensors are regular O2 sensors before I swap them around. The sensors were most likely up to temperature but the exhaust and coolant definitely wasn’t
