Jeep Cherokee- p0420

My wife’s Cherokee has p0420 error. The car is a 2016 with 55k miles on it. The error suggests it’s a catalytic converter error. My best hunch is it’s an sensor. Sensors aren’t covered anymore under the warranty but the cat is.

Is my best bet to contact the dealer and report the code? If it’s the car than they will fix under warranty right? If it’s the sensor then they wouldn’t … but i imagine the cost to fix the sensor at the dealer wouldn’t be that much more than a small garage.

If it;s the cat!


At the dealer.


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If not its PAY,PAY,PAY. LOL
dealer will probably charge you at least $200

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Is the engine burning any oil? I wouldn’t expect that on a 2016 with only 55K miles…but maybe it’s a Jeep thing I don’t understand.

Personally I’d take it to the dealer, get their take, just in case it is the catalytic converter. If it’s not, be prepared to pay them for their diagnostic time. If they determine it’s a sensor, then take it to a local independent shop.

No oil leak. Doesn’t seem to have any performance issues at all. Personally I don’t think it’s the cat. But with the warranty the dealer seems like the smart move

Any idea what they’d charge for daignostic? What about sensor? Would diagnostic charge be applied toward that repair? My fear is that if I take it to a local shop they will also do their own diagnostic and I’d pay again.

Only the dealer where ever that is can answer that charge question . And yes the independent would more than likely have a diagnostic fee also so just have it fixed by the dealer and not pay for 2 diagnostic fees.

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Makes sense about the charge for sure. That said what do you think is a reasonable diagnostic fee and bill to replace the o2 sensor.

I would hope all told under 400

How would I know ? Pick up your phone and ask what the diagnostic fee is and if it applies to the final invoice after the work is done.


Any history on this vehicle, something that happened in the past that might have damaged the cat? Misfiring? Clogged air or fuel filters? Bad gasoline? A lot of high speed driving for very long distances? Ignored check engine lights?

Nope literally nothing other than check engine light popping on. It runs fine. I would be pretty surprised if it was the cat but with the warranty I’m sort of bound to the dealer

Jeep Grand Cherokee P0420: Catalyst System Efficiency → Below Threshold → Bank 1 | Drivetrain Resource (

I say it is probably the o2 sensor.

Because I’m a cheapskate and a firm believer in the idea that I check the simple things first, I’d look to see if the air filter has ever been changed. If not, just do it. Then reset the codes (clear this one) and see if it resets.

Given what the OP says, good chance it is just one of the two O2 sensors. A shop with the right diagnostic equipment should be able to inspect the signals from each O2 sensor as the engine is idling. Just by plugging into the OBD II port. The signals are supposed to track each other in a certain way.

I had a 2016 vehicle today with 25,000 miles, fault codes P0420 and P0430; catalyst efficiency below thresholds, bank 1 and 2.

I was in disbelief of a (or 2) catalyst failures on a vehicle with low miles. I have the “right diagnostic equipment” that would prove the failure by reading the sensor input, however; I raised the car to find the owner had installed a “Cat back” exhaust system resulting in very minor exhaust leaks near the downstream sensor.

Exhaust leaks that are too small to emit noise can draw in oxygen and foil the catalyst monitor.

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good point.