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8

It was indeed the catalytic converter (the EX does not have a pre-cat). After replacing it, the downstream sensor graph spends most of its time above 0.5 V, as it should if the converter is working. Update: I started getting this error code again, a little over a year after replacing the cat. I also finally found a guide on how to read these graphs, from ...


5

If you have rattling on acceleration and the fuel economy is depressed, it is very likely that the catalytic converter core has cracked and it is blocking the exhaust now. You can try to measure its efficiency first by looking if the rear O2 sensor voltage reading after heating is steady (so the catalytic converter is good) or jumping (so it is bad). If it ...


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Because it's dangerous with erroneous data This is actually very smart on Subaru's part. I have to give them credit. If you have sensors that are faulting you could be giving an ECE false or eroneous information. The ECU would then take that false data and make adjustments to traction control and engine power. You could be on a wet or icy surface, step ...


5

Excellent graphs. The after catalyst sensor shows normal mixture readings. The PCM can and will operate the system lean or rich depending on operating conditions. The voltage will rarely be held at any intermediate voltage, such as 0.5 volt. This is an urban legend not based on engineering fact. The rear sensor voltage should remain steady at any steady ...


4

I say "no". Do you live in a place that requires an emissions (no CEL check-engine light) inspection? And would you need same by August? P0420 is what is referred to a "Catalytic Converter Efficiency". It is basically referring to how well the catalyst is converting hydrocarbons, carbon monoxide, and NOX. The P0420 code can be caused by a whole bunch of ...


3

The cooling and emissions systems aren't directly related. A loose radiator cap will cause the system to not pressurize, which will cause the coolant to boil at a lower temperature. You can't rely on your temp gauge for this. If the engine is not running at it's normal temperature, it is possible it will affect the emissions coming out of it. Did you see ...


3

It definitely sounds like you have a serious issue with the catalytic converter and should have it replaced. Replacement with a universal converter should not be expensive. In expensive Silicon Valley (and air conscious CA) I got a replacement for $220 at a specialist shop. However, the failure of your catalyst is a symptom of another issue and not a cause, ...


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Dealing with mechanics If you're going to take it to a mechanic anyway, you are probably better off letting that same mechanic do the diagnosis and obtaining the correct part(s). Bringing parts and a diagnosis to a mechanic is likely to get as warm a reception as bringing your own eggs and raw bacon to a restaurant and asking them to cook you breakfast. ...


3

The P0420 and P0440 are completely unrelated (other than both being related to emissions). The P0420 is having to do with catalyst function. The P0440 having to do with EVAP system. There is no way for one code to have morphed into the other code. P0420 can appear and disappear over time due to the nature of what is being seen by the computer. If the after ...


3

DTC P0420 - Catalyst system efficiency below threshold (bank-1) DTC P0457 - Evaporative emission control system leak detected (fuel cap loose/off) First let's look at the P0420 causes include: Exhaust leak Catalytic converter Rear O2 sensor circuit The computer compares the pre- and post-cat O2 sensors readings to determine if the cat is working ...


2

Okay, I fixed it. Turns out, I had a bad catalytic converter and I was reading the wrong thing in my original post. I identified the bad cat by looking at the correct sensor data. The data posted (red and blue) is the lambda measurement, which is a derived (not actual) measurement. It's useful for the forward A/F, but useless (as far as I have seen) for ...


2

The Prius has an exhaust system unique to the Prius. As it is a hybrid the engine does not operate continuously, and so the cat has to be a special case in retaining its temperature to 'light-off'. Exhaust vacuum valves and controls require servicing; heat adsorbers have to be working; air/fuel ratio sensors are used as against a straight forward O2 sensor ...


2

P0420 is probably the most common code seen. It refers to "Catalytic Converter Efficiency" Basically, it Engine Control Module (ECU) monitors the chemical constituents of the exhaust, both before and after the catalytic converter. The Catalyst is really a small furnace that reburns the exhaust and adds more oxygen where necessary, to eliminate harmful ...


2

Four things can throw this P0420 code, Bad catalytic converter bad upstream O2, bad downstream O2, fuel ratio problem, rich or lean, which can be even more complicated to sort out as suggested in the article.


2

Essentially the technical meaning of a p0420 is that the downstream o2 sensor is detecting an inconsistency with fuel trim. Generally this is code is associated with a bad catalytic converter. Many things can cause this code, but usually the easiest ways to figure it out are testing it with a hydrocarbon analyzer. The dealership usually has one of these. If ...


2

Not familiar with Honda ignition systems, but could even be a cracked coil or power transistor case that's allowing moisture in. Acts up until the moisture is cooked out of it.


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There is actually a letter that was sent out (I also have a 2011 Chevy Equinox with this issue and just had my cat. conv. replaced because of it) saying there may be thermal damage or melting on it and if you have this issue to take it to your dealer to get it repaired. Did you get that letter?


1

Your mechanic may be right, or at least think he is. For Engine code CCTA, there are two converters - one in the space of that "lump" in the left side of your picture, and the so-called "center" converter. The primary converter probably isn't large enough to handle the whole cleanup on the turbo CCTA engine. That may not be the right picture for your ...


1

I'm going to guess and say it is not technically defective, but just smaller in size than the original. If you are clearing the code each time, it may take a few days for the ECM to pass all of the required tests before it even looks at catalyst efficiency. If the code is going away on its own and then coming back, then the efficiency of the new converter ...


1

There are as many different strategies for deteriming catalyst failure as there are vehicle manufacturers. All the formulas are propritary, even a deep dive into SAE technical papers on the subject will reveal little about the details of the varius strategies. It is easier to say what the post catalyst sensor waveform of a working catalyst looks like than ...


1

p0420 is caused by a damaged catalytic converter or O2 sensor. Since you said that the vehicle had a misfire code, they most likely drove with the light on because they figured they would sell it. The Catalytic Converter is a giant oven that stores and releases oxygen. Dumping fuel, from the misfire, destroys the honeycomb inside the cat which contains ...


1

I don't think the secondary O2 sensor is reading properly. If the cat were actually shot (a legitimate P0420 code) the bottom graph of secondary O2 should be very similar to the top "primary" O2 aka "Sensor 1". Keep in mind the cat needs to be fully heated for these graphs to be the most useful. Your pictures look like the Torque cellphone app for a ...


1

It can be many things I mean, way many things, as SteveRacer has already cited. The most common (but not unique) is a failing catalytic converter. Please note that often a bad catalytic converter usually is a symptom of a problem, not a cause. If you replace it without solving the source problem, it will fail again in very short time. If this is the case ...


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Possibly a failing fuel pump or pressure regulator. Have the fuel pressure checked in addition to @Rory suggestion.


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I'm just wondering why you aren't considering the downstream O2 sensor as being the culprit? If it is sending back erroneous information back to the computer, the computer might think the cat is bad. The O2 sensor can be bad (or on the way out) and never throw a code. Something an O2 will do over time while going bad is get what is called lazy. Normally, ...


1

The problems you are experiencing will have nothing to do with the transmission. Here is what the code explanation is. My feeling is it's with the Fuel pump driver module. It may be going bad. Code: P1233 - Fuel System Disabled or Offline Description: The PCM monitors the fuel pump monitor (FPM) circuit from the fuel pump driver module (FPDM). With ...


1

Which O2 sensor did they change out? You wrote he changed out B1/S1 which would be the one pre-cat or the first one (upstream) which actually adapts the fuel to running conditions. The one which should have been looked at is B1/S2, or the one which is downstream ... the second one which its only job is to check how the cat is doing (mainly to check to make ...


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The code P0420 is "Catalyst Efficiency below threshhold" First check the exhaust gases on a emissions gas tester. If the CO2 and CO together are less than around 14.5% with the engine in good condition, no faults- then you are looking at a defective cat.


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If the O2 sensor is replaced then the code could also be caused by a bad engine coolant temp sens. (Don't ask me how, fun thing about Cobalts). Before you buy that, also look for manifold and exhaust leaks.


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The info I have found under the federal emissions warranty says it is covered for 8 years or 80,000 miles. If you have had all the service work done at the dealer I would complain to the dealer, the Nissan area rep. and anyone else who will listen. The next thing I would do is get a second opinion. Find out why it failed so it doesn't happen again. Check ...


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