P0420 intermittent check engine light.

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Which device and or app are you currently using to read the stored OBD2 codes?

If throwing parts at the car, you might start with a new OEM/Denso upstream A/F sensor, as that aftermarket sensor could be acting up.

How many miles are on the vehicle currently?

FYI : you're moderated until you've posted 5 times.

 

Often after market cats don’t pass your cars computer checks.

 

With some exception, they don't install aftermarket cats in California due to state law, so that's likely not the issue. But taking car back to shop that did the work would be wise to see what they say...

Separate from that first thing I'd do with this one is find out where the vehicle is in relation to 100K mile tune up with new spark plugs, air filter, MAF sensor cleaning, throttle body cleaning and 12v reset to see if that cleans up the problem. Then if that didn't work I'd clean and inspect O2 sensor and if that didn't work I'd replace the sensor because the replacement cat is still new, I'd not be suspicious of that being the source.

 

The only reason why I said aftermarket cat sometimes fail is because he said they used one. I know they live in California but, there’s ways to get aftermarket cats still.

 

Well... California now sells an aftermarket cat in the near $1K range that passes smog inspection. So it's possible that it is a legit cat.

As for aftermarket cats failing at an early age, do you have any references? I'm on Priuschat every day and I have yet to see anyone posting about how their aftermarket cat failed earlier than expected. If I did find out about that I'd be very concerned and want to know about it. So if you have any references I'm eager to find out.

 

Yes, I have read on here several times about people getting the P0 420 light on from installing a aftermarket cat. Also coming from a Smog technician standpoint there are less precious metals in the aftermarket cats. The aftermarket cats do not clean up emissions as well as a factory ones. I cannot show you the data because I do not have pictures of the smog machine showing us. So I guess you could just call it my opinion because I don’t have proof to show you. Probably a reason that the thieves do not steal aftermarket cats as often is because of the fact that there’s not as many precious metals in them.

I guess an exception would be a carb approved cat. I believe magna flow makes one for California.

 

I believe the P0172 code is a running lien code. It might be related to cleaning the mass airflow. See what codes come back.

 

We've done a small amount of DIY research on emissions of aftermarket cats on here... And though the newer cats have less precious metals in them, the design is far more advanced/efficient than what they were building 15 years ago for Prius, so less metals are required to achieve similar results. Can't remember the link but the conclusion was at low RPM an aftermarket cat's emissions were slightly cleaner than OEM gen2 cat. The person doing the analysis @TMR-JWAP did a thorough job, but due to limits on DIY analysis equipment was unable to do emissions testing at higher RPM under load so it is possible that an aftermarket cat is less efficient in that scenario because we've not been able to study that yet.

 

Have you got new codes since you cleared the light?

 

that’s AWSOME people are researching the aftermarket cats.

 

The O2 sensor that has wires passing through the passenger side floor board is the downstream sensor. The upstream (fuel ratio sensor) is mounted in the exhaust manifold and plugs into the car harness under the inverter. The downstream O2 sensor is mounted in the exhaust pipe between the upper catalytic converter and the downstream catalytic converter, and it's wires pass through the floor board and plug into the car harness on the left side of the front passenger floorboard tunnel.

When DTC P0172 is recorded, the actual air-fuel ratio is on the RICH side.

Detection Condition:
When air-fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on RICH side (2 trip detection logic)

Trouble Area:
Injector leak, blockage • Mass air flow meter • Engine coolant temperature sensor • Ignition system • Fuel pressure • Gas leakage in exhaust system • Open or short in A/F sensor (bank 1, sensor 1) circuit • A/F sensor (bank 1, sensor 1) • A/F sensor heater • EFI M relay • ECM

 

One thing I have seen that always amazes me is the amount of carbon dust that will come out of a Prius cat when compressed air is blown through it.

try it sometime. Remove the entire front section of pipe, cats and resonator. It should also have the O2 sensor removed. Use a decent compressor with a good venturi style air multiplier nozzle. Plug the O2 hole and then blow air backwards through the pipe and then blow air through the O2 hole. You'll be amazed at the huge cloud that comes out. Worth a try to see if it clears up the P0420