Permanent p0420 code after valve cover leak

[fknMeow]

Hi guys, I'm wondering if someone can help me out here.

22 JLUR 3.6 manual with 57k miles...

So a couple of weeks ago I started getting the blinking check engine light and the car started driving like shit, it was throwing a bunch of codes, among them. P0137...long story short, it's was the valve cover that dripped a little bit of oil on the downstream O2 sensor, and that just snowballed into a bunch of other codes. I replaced the sensor and cleared all the codes, and the car is running perfectly fine now, but it still has the p0420 code and I've probably driven a good 400 mi already so I feel like it would have cleared by now. It's throwing a check engine light a couple times that I've cleared, which was just an active or pending p0420...but when it's just the permanent code there's no light on.

When the whole thing first happened I did have to drive about 120 mi with the bad sensor and poor performance, Getting like 10 miles a gallon. The wife had a family emergency so it wasn't really an option to stop and figure it out then.

So I'm wondering, could the cat really be bad? Has anyone ran into this or have any suggestions on what I could do to try to clear this up?

Thanks!

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[fknMeow]

Any thoughts at all? Could the cat really be fried?

 

[mwilk012]

Without looking at the live data reading from both the upstream and downstream sensors, its impossible to tell. Driving 120 miles with a maxed out rich bank is a terrible idea and there is a good chance you did some permanent damage to the cat. If your lucky, it might clean up eventually.

 

[fig523165]

Any status update? I had the same scenario with my JT.

 

[fknMeow]

Any status update? I had the same scenario with my JT.

Still there, reset it periodically but not luck getting rid of it, comes back after driving 40 or so miles. Looks like I'll be replacing the cat soon.

 

[fig523165]

Heard it can take quite a while to reset if you don't hit all the "basic drive" requirement. I'm considering replacing the upstream sensor too. I only replaced the downstream 100mi ago, but jscan is still showing P0420 as active.

 

[alphawolff]

Generally after replacing the O2 sensor(and leak) you want to reset the fuel adaptives in the PCM, as that previously failed side has it usually maxed out and can cause a lean/rich DTC to return if it isn't reset.

That being said it's totally possible driving for too long in that condition can dump so much additional fuel onto that bank that the cat begins to melt/fail. If you fixed the issue and have put 500+ miles on it and the P0420 keeps coming back than it is a failed cat. I've replaced probably well north of 100 of these sensors for this exact same issue and I don't think I've ever seen a failed cat out of it. Hell, I've got one in my queue right now waiting for a backordered O2 sensor to show up.

Heard it can take quite a while to reset if you don't hit all the "basic drive" requirement. I'm considering replacing the upstream sensor too. I only replaced the downstream 100mi ago, but jscan is still showing P0420 as active.

Just some future reference here, but the p0420 code can not throw unless the o2 sensors pass their own integrity check. A p0420 code is a failed cat 99.99% of the time. Sometimes the cat is just on the verge of failing and once the code is cleared can sometimes take awhile to come back or not come back at all. I suspect this is where the "replace sensors first" idea came from. It's just placebo.

You can verify a failed cat by monitoring the upstream/downstream voltage readouts. The upstream will jump around depending on accelerator positions, while the downstream should remain relatively stable. If the downstream ever jumps to meet the upstream, it's a failed cat.

 

[fknMeow]

Generally after replacing the O2 sensor(and leak) you want to reset the fuel adaptives in the PCM, as that previously failed side has it usually maxed out and can cause a lean/rich DTC to return if it isn't reset.

That being said it's totally possible driving for too long in that condition can dump so much additional fuel onto that bank that the cat begins to melt/fail. If you fixed the issue and have put 500+ miles on it and the P0420 keeps coming back than it is a failed cat. I've replaced probably well north of 100 of these sensors for this exact same issue and I don't think I've ever seen a failed cat out of it. Hell, I've got one in my queue right now waiting for a backordered O2 sensor to show up.



Just some future reference here, but the p0420 code can not throw unless the o2 sensors pass their own integrity check. A p0420 code is a failed cat 99.99% of the time. Sometimes the cat is just on the verge of failing and once the code is cleared can sometimes take awhile to come back or not come back at all. I suspect this is where the "replace sensors first" idea came from. It's just placebo.

You can verify a failed cat by monitoring the upstream/downstream voltage readouts. The upstream will jump around depending on accelerator positions, while the downstream should remain relatively stable. If the downstream ever jumps to meet the upstream, it's a failed cat.

So I'm guessing that this would indicate a failed cat?

 

[alphawolff]

So I'm guessing that this would indicate a failed cat?

I'm going to be honest that is the worst graphing scan tool readout I've ever seen. Oxygen sensor "1" or oxygen sensor "2" means what? They're 1/1, 1/2, 2/1, and 2/2. No idea which sensor correlates to what here. No idea if this was tested during a drive, accelerator conditions, or anything. Hell, don't even know what scale this is, or what each point tested at.

Sensor 1 (i assume this is sensor 1/1?) doesn't even change voltage, which is impossible unless you're just idling it and nothing else.

You need to monitor the right bank upstream and downstream voltages (sensor 1/1 and sensor 1/2). Sensor 1/1 should jump voltage constantly with throttle input going representing the constantly changing fuel mixture. The downstream should stay a relative constant voltage. This test should be performed on a test drive.

 

[AnnDee4444]

I would check to see if the replacement sensor is good by swapping side-to-side.

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