[Sienile]

I asked about the scanner for the engine light when codes are gone. It makes no sense for it to be on if there are no codes, unless it's just not codes the scanner is capable of reading. There are some cheap scanners that will only give you early OBD2 codes and some codes that were added to the standard in the mid to late 2000s won't be detected. Unfortunately, some of those "cheap" scanners cost over $100, so price isn't always a good metric.

 

[Valhallalla]

I asked about the scanner for the engine light when codes are gone. It makes no sense for it to be on if there are no codes, unless it's just not codes the scanner is capable of reading. There are some cheap scanners that will only give you early OBD2 codes and some codes that were added to the standard in the mid to late 2000s won't be detected. Unfortunately, some of those "cheap" scanners cost over $100, so price isn't always a good metric.

My comment regarding "high tech scanners" was not directed at your other post and I'm sorry you might have taken it that way. I agree with what you're saying. My post was meant to point out that it's not terribly difficult to diagnose this DTC. There is nothing in the diagnostic test that can't be done by a vehicle owner with moderate skills and no special tools are needed. In other words, regardless of how expensive their equipment is or how highly trained their technician may be, the dealer is not gonna be able to tell the OP anything they probably can't determine on their own. There are only a handful of possible causes and they are all pretty easy to check.

 

[Sienile]

Yeah, the P0420 is simple. Only a handful of things it can be. The phantom code keeping the light on is the confusing part.

 

[ggoose]

Not knowing what brand the replacement O2 sensor is, I would suggest replacing both the upstream and downstream sensors. Replace with NTK, OEM, or Denso only - definitely no Bosch or auto parts store variety. Chryslers do not play well with bosch o2 sensors.

Review the p420 diagnostic procedure valhalalla posted. Note replacing the cat was the last step.

One of the metrics for determining the p0420 is how the downstream O2 sensor compares to the upstream O2 sensor. The upstream should continually be updating/bouncing around to reflect engine air/fuel mix where the downstream O2 sensor will be relatively steady since the cat cleans up the exhaust gas. If the upstream sensor is going bad it may not be reacting as it should and when compared to the downstream sensor there may not be enough of a difference and the p0420 is set.

If the check engine lamp is on, there is a dtc.

 

[transistor]

I have ordered the upstream O2 sensor and will follow the procedure to try and diagnose. I appreciate the assistance.

 

[mikeypoo]

I have ordered the upstream O2 sensor and will follow the procedure to try and diagnose. I appreciate the assistance.

Curious what you find out. If all else fails and you're ready to throw in the towel or want to get a definitive diagnosis before you go replacing the converter you're only a couple hours away from scenic Avoca. Take it to Eric at South Main Auto and tell him Mike the crusher guy sent you. Your car might even get featured in one of his youtube videos

 

[transistor]

Curious what you find out. If all else fails and you're ready to throw in the towel or want to get a definitive diagnosis before you go replacing the converter you're only a couple hours away from scenic Avoca. Take it to Eric at South Main Auto and tell him Mike the crusher guy sent you. Your car might even get featured in one of his youtube videos

I ordered the NTK upstream sensor and I will report back after it is installed with the results. Thanks to all for the input.

 

[damianremodeling]

UPDATE: Cleared the P0420 code just for fun. Went almost 400 miles. No code return.

Brought it in to have Cyl 2-6 spark plugs and coils replaced (already had cyl 1 done when it was misfiring with P0301 code which never returned.)

Also had bank1 downstream O2 sensor replaced.

Picked up yesterday, went about 50 miles and P 0420 code returned. Engine runs strong, no issues whatsoever. Also, it has been very cold here in Bufffalo NY , around 10 degrees last week or so.

Is there a definitive test that will tell me for certain if the Catalytic Converter is bad? Remember, Im in NY with California emissions, otherwise I would just replace it. Thanks for any input, I appreciate it.

I've had similar issue , Shop replaced catalytic converter because of a long lasting misfire problem it was clogged .
Misfire was fixed and new spark plugs injectors and upper oxygen sensor replaced. BUUUT thy didn't cahnge the downstream sensor --- they said it was good.
Well it turned out ...even if it "good" when you have an old and new O2 sensor on the same bank (pipe) it gives the catalytic converter inefficiency code ..... I just installed a new O2 downstram myself . it's like 30$ of amaon - Bosch .
Code cleared. no problems.

 

[newgrowthcontracting]

I ordered the NTK upstream sensor and I will report back after it is installed with the results. Thanks to all for the input.

Well did it work?

 

[Wss76]

Any update on it o2 sensor fixed it