Intermittent P0420

[Wilsonb80]

Just wondering if anyone else get the P0420 check engine light. Intermittently?

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[whysoserious]

Nope. Not yet anyway.

 

[Hootbro]

P0420 for Catalyst System Efficiency Low is not a common stand alone code seen.

Google Foo shows a long list of possible causes. So unless you want to shotgun a bunch of parts, might be worth having it professionally diagnosed.

 

[Wilsonb80]

Just find it odd that it comes and goes on its own.

 

[DylanM]

Code: P0420
Definition: Catalyst Efficiency (Bank 1)
General Operation: The State of Change (SOC) catalyst monitor uses the signals from both the Upstream and Downstream Oxygen (O2) Sensors to detect aging of the catalyst. The Upstream O2 Sensor slow response monitor runs simultaneously to determine if the sensor signal is plausible. A pass/fail determination is made on the O2 Sensor slow response diagnostic before a catalyst determination is made to prevent a false fail of the catalyst monitor.
Cause:

• O2 SENSOR 1/1 RETURN CIRCUIT SHORTED TO GROUND
• O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND
• O2 SENSOR 1/1 RETURN CIRCUIT OPEN
• O2 SENSOR 1/2 RETURN CIRCUIT OPEN
• EXHAUST LEAK
• ENGINE MECHANICAL CONDITION
• AGING O2 SENSOR
• CATALYTIC CONVERTER

With the fault code being intermittent in nature, I'd check the o2 sensor harnesses to make sure they're not resting on hot exhaust components or abrading on anything, make sure the 02 sensor connectors are firmly mated, and look for any evidence of exhaust leaks near the upstream o2 sensors or manifold to cylinder surfaces. If you have access to a scanner with live data, you could also look to see if you have an erratic or lazy sensor signal.

 

[Wilsonb80]

thank you, i will see if the harness is clear and connections good.

 

[Brahmajoe]

Just jumping in here, looking to change out my upstream bank 1 sensor. Is the harness easy to access under the fender liner?

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