P0420 Code

[ctennison]

So I got the P0420 code. I have a 2017 2.4L and its hard for me to believe the cat is bad. I've replaced both O2 sensors, new plugs, filter, cleaned the throttle body and almost every sensor in the car. Any ideas before I spend the money for a new cat?  

[5rebel9]

What kind of driving do you do and what other CEL codes have you had in the recent past with the J? If a lot of short drives are done , put a good dose of Seafoam fuel system cleaner in the fuel tank and DRIVE highway speeds for the tank over the course of a week and see what it does. The 2.4 is not known to be that troublesome a motor. Also inspect the exhaust system for any cracks or openings between the upstream and downstream O2 sensors, They can throw some pretty weird codes if air can get in before the downstream sensor. And it is the downstream sensor that is the primary trigger for the P0420 code, Note these motors are also pretty finicky on OE brand sensors, Hope you used OE.

[ctennison]

No other codes, not running bad, not doing anything other then the P0420 code. The O2 sensors are bosch. I can clear it and sometimes it will come right back on or it will be a few days. It always does it under 2,000 RPMs and about 50 MPH.

[5rebel9]

I've had mopars for over 25 years and never had good luck with BOSCH brand O2 sensors. I'd suggest try replacing the downstream one with an OE brand like NTK(or NKT...I'm partly dyslexic ,,,LOL;) )

  Run some Seafoam in the fuel, it will also help clean out the converter. 

[ctennison]

I'll give it a shot, thank you.

[Migit]

I have a 2018 journey and I changed my cat about 6 months, and both O2 Sensors about 2 months ago. And now I'm getting the PO420 Code. Any idea on what I should do now?

[Dean H]

 

What engine 2.4 or 3.6 ?

 

Have you tried disconnecting the negative battery terminal and waiting a few minutes, to reset the PCM?

 

 

P0420-CATALYST EFFICIENCY (BANK 1)

 

Theory of Operation-

 

The State of Change (SOC) catalyst monitor uses the signals from both the upstream and downstream 02 Sensors to detect aging of the catalyst. Based on the fact that when a catalyst ages, it loses some of its Oxygen Storage Capacity (OSC). As a result, part of the untreated exhaust gases can breakthrough the catalyst and causes the downstream O2 Sensor to deviate from its neutral (Stoichiometric) position. By observing the activities in the downstream O2 Sensor signal, located in the exhaust path behind the Catalytic Converter, the degradation level of catalyst can be detected. In general, the higher the downstream O2 Sensor SOC value, the more exhaust gas breakthrough and the lower the Oxygen Storage Capacity of the Catalytic Converter. The Downstream O2 Sensor response monitor is intended to diagnose a Downstream O2 Sensor that is not moving or stuck in a voltage window and to insure accurate information for catalyst monitor diagnosis.

 

 

POSSIBLE CAUSES:

 

NOTE: 

 

A new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. 

 

NOTE:

 

If an O2 Sensor DTC set along with the Catalytic Converter Efficiency DTC diagnose the O2 Sensor DTCs before continuing.

 

NOTE: Check for contaminants that may have damaged the O2 Sensor and Catalytic Converter: contaminated fuel, unapproved silicone, oil and coolant, repair necessary.

 

 

02 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND

 

02 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND

 

02 SENSOR 1/1 RETURN CIRCUIT OPEN

 

02 SENSOR 1/2 RETURN CIRCUIT OPEN

 

EXHAUST LEAK

 

ENGINE MECHANICAL CONDITION

 

AGING 02 SENSOR

 

CATALYTIC CONVERTER

Edited October 1 by Dean H

[diymirage]

You can always find a tuner to shut off the rear O2 sensors 

 

They serve no purpose than aiding in the government overreach