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Topic
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Car in question is a 2005 Hyundai Elantra with California emissions. 131k Miles.
About 4 months ago P0420 was set and after taking some temperature readings the temperature got colder at the rear of the cat and rear o2 voltages were all over the place so I thought it was a safe bet.
I replaced the cat along with the rear o2 sensor and all has been well for 2500+ miles.
P0420 has now come back along with P2251 (B1S1 Current Control Open) so being the front o2 sensor has unknown mileage on it and the wiring checked out, I replaced it.
P2251 is now gone, but the front o2 sensor is showing a steady 1.8-1.9V at idle. With a stab of the throttle is does respond quickly and shoots up to 4v or so, but I have no idea if that is even accurate? As far as I know the voltages should both be measured between 0-1V but this is a 5 wire wideband sensor and I’m not sure if this is an issue still?
P0420 is not back after 15 miles and the cat does have that bronze look to it like it’s been melted, and my temperature readings are colder again on the outlet again.
Any help dissecting this bitch would be appreciated! B)
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How are the longfeultrims and the shortfeultrims? What are the MAF/MAP readings, feulpresseure ok? No airleaks in the inleat- or exaustsystem?
How is the ignition system working? a faulty coil pack in the past can cause a cat to burn out, just replacing a cat without taking away the original problem is a guarantee for a returning problem and a waist of money
Fuel Trims are out of spec, 12+ on the STFT and -2.3 LTFT. Fuel pressure is good, no air leaks. Not sure on MAF readings. Car isn’t here to check now.
Car is running perfectly otherwise, with no adverse running conditions.
I’m not just throwing parts at the car and have only replaced items which have been confirmed to be bad.
The problem whit P0420 is, that the cat only can be replaced after the orgine of the problem has been identifeed. If you do other whise 🙁 -2.3 on the long aint that bad, that is actuly normal. Not any that i would be consindering as a part of the problem 😉
The +12 is part of the enrichment for the catalyst to do its job, it can be to +25/-25, so it aint that bad :cheer: .How did you check for airleaks, breakcleaner of a smokedetector? A nasty pipe maybe the vacumhose to the brakebooster, whitch can cause this isseu 😉
My experience is that if the STFT and LTFT run much past 10+ or – cumulatively it will cause an issue.
Brake clean and visual inspection for the air leaks.
Like I said, the car runs perfectly just has P0420 and needs to clear before inspection.
I see now that you have a wideband sensor, missed that part, you need to check the ampflow of itm whit either a diagnostic tool, or a good clamp ammeter, i use a automotive scoop for these sensors to check them. You will need to figure out what kind of brand of sensor you have, to determine what kind of measurementyou will do, on a Bosch and NTK volt measerments are possible, altough i tend to go for a clamp ammeter.
Ive added a measerment as a example how a wideband sensor shutlook like on a volt and am measement, not saying, that youre vehicle is the same, but just to give you a idea of a bosch wideband
The top one is the pump cell, this one has to be around the 0.45V, if you accerate or decerate it can go up or down depending on the mixture state. It will puls up an down 8 to 10 times a second, it can be even more when going to accelerate ;).
The second one is the amflow of the pumpcel, not sure why my scope shows my measerment as a volt , but that aint the point, you can see that the pumpcel is moving O2 parts in or out of the wideband sensor to keep a λ=1.A P0420 is generated by looking at the rear sensor but comparing it to the front (the Linear AFS in this case). Since the problem with the front sensor was repaired, the car should at least be driven enough to complete the catalyst monitor and see if the P0420 resets before continuing diagnosis. You could also drive it while using a graphing scan tool to watch the rear o2 activity. While holding a steady throttle/load, it should be fairly stable. You can’t visually compare it to the front on the scan tool the old-fashioned way because it’s a LAFS, but the back should not be switching the way a standard front o2 normally looks.
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