# Three catalytic converters in a month (P0420)



## Rynoguy91 (Nov 28, 2020)

I have a 2014 Cruze LTZ with ~110,000 miles on it. My CEL came on at the end of October; OBD II scanner gave me code P0420. I took it up to Firestone, and they replaced the front O2 sensor and burned-out catalytic converter, as well as repaired/replaced the leaking head gasket and leaking transmission fluid line which they said caused the converter failure.

I drove it for a little under two weeks before the CEL came back on with the same code (P0420). During those 10-12 days, I drove approximately 450 miles, and all of the telltale signs of a converter failure were absent: no sluggish acceleration, no lurching or surging during automatic shifting, etc.

I took it back to Firestone, and they told me the converter they installed must have been “defective,” so they installed a new one free of charge. Once again, the issues were resolved, and I drove the car for another 10-12 days and another 450 miles before the CEL came back again. Same code as the last two times.

Now Firestone is saying they have no idea what’s wrong with it, they’re going to put ANOTHER converter in it, and if that one goes, I have to take it to a dealer because the car’s computer may be the issue. (To their credit, they’re also offering a refund for the cost of the converter if this latest attempt doesn’t work.) Can anyone provide me some clarity/validity as to what’s going on here? Why install a third converter if you even suspect it’s just going to burn out again? I’ve read online of GM having some software updates for the Cruze’s emissions system, but I would’ve assumed my car had received it by the time it came into my possession. I would also like to assume they checked the O2 sensors’ wirings and the exhaust system for leaks at least one of the three times I’ve taken it to them.


----------



## Thebigzeus (Dec 2, 2018)

Sounds like its dumping raw fuel or oil into the new converters, or they are just aftermarket junk. Need to look into them when they take them off. Do they smell like fuel or oil, are they discolored? If not they are likely just cheap and inefficient and setting the code.


----------



## Rynoguy91 (Nov 28, 2020)

Thebigzeus said:


> Sounds like its dumping raw fuel or oil into the new converters, or they are just aftermarket junk. Need to look into them when they take them off. Do they smell like fuel or oil, are they discolored? If not they are likely just cheap and inefficient and setting the code.


Yep, I really should’ve asked to see the first two after they were removed, but didn’t 🙄 I’m really hoping it’s your latter idea! I’ve suspected it might be aftermarket converters, as well, but didn’t think to ask after they said the first one was just “defective.”


----------



## Thebigzeus (Dec 2, 2018)

Rynoguy91 said:


> Yep, I really should’ve asked to see the first two after they were removed, but didn’t 🙄 I’m really hoping it’s your latter idea! I’ve suspected it might be aftermarket converters, as well, but didn’t think to ask after they said the first one was just “defective.”


I had a family member who went through 2 ebay converters (on a different car) all set a check engine light. Ponied up and paid Toyota for a genuine, and no codes in the future. So I have a feeling it may be a good suggestion. You can always buy a low mileage used one that still has some life left in it to save some $$$.


----------



## mg512 (Dec 17, 2020)

I had similar issues on a Honda. Aftermarket catalytic converters are usually not to the same standard as OEM and the sensors are very touchy. I’ll keep it in mind if I ever have a similar problem to inspect the cat. Have you thought to ask the service center and maybe one of them remembers the state of the converter.


----------



## Valpo Cruze (Feb 23, 2014)

To get 2 bad cats and now possibly a 3rd is a statistical anomaly.

If you have a 1 in 1,000 chance of getting a bad cat then the chance of getting 2 is 1 in 1 million and getting 3 is 1 in 1 billion. If that is truly the odds you have then go buy a lottery ticket.

Statistics says its not a cat problem but the bad cats are a symptom of what is going bad. In the 450 miles you drove it between cat problems how did the car run, how was the fuel economy? How old are your spark plugs, air filter? Have you or they tried to do any data logging or checking for codes deeper than just pulling codes out of the ECU?

Do you have a better garage in your area? My experience with the Firestone dealers in my area is that while they are great with tires and brakes, they are not great with mechanic work. Yeah they know how to change parts but they may not understand why the part went bad and if it was the problem or the symptom of another problem.


----------



## Thebigzeus (Dec 2, 2018)

Venomized262 said:


> To get 2 bad cats and now possibly a 3rd is a statistical anomaly.


Not if they’re aftermarket


----------



## Blasirl (Mar 31, 2015)

A code *P0420* may mean that _one or more of the following_ has happened: 

Leaded fuel was used where unleaded was called for (unlikely) 
A damaged or failed oxygen / O2 sensor 
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly 
The engine coolant temperature sensor is not working properly 
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe 
Failed or underperforming catalytic converter (likely) 
Retarded spark timing 
The oxygen sensors in front and behind the converter are reporting too similar of readings 
Leaking fuel injector or high fuel pressure 
Cylinder misfire Oil contamination
Read more at: P0420 Catalyst System Efficiency Below Threshold


----------



## KENSTV123 (Sep 21, 2014)

This should be added-especially the 100 degree difference, a cheep IR sensor would easily show this---

"Some suggested steps for troubleshooting and fixing a P0420 error code include: Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required. Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady). Inspect the downstream heated oxygen sensor, replace if necessary Replace the catalytic converter Diagnostic Tip Generally speaking you can look at the temperature of the exhaust just before and just after the converter using an infrared temperature gun. The output should be about 100 degrees Fahrenheit hotter when the engine is fully warmed up. Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (02 sensor). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily. We strongly recommend that if you need to replace the catalytic converter that you replace it with an original manufacturer brand unit (i.e. get it from a dealership). Second choice would be a high-quality replacement part such as a 50-state legal cat. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter. One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into."

Read more at: P0420 Catalyst System Efficiency Below Threshold
Copyright OBD-Codes.com


----------

