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MoodMan
Novice
Jun 2, 2022, 9:49 AM
Post #1 of 8
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P0420 Code vanishes
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So I had a P0420 code for a couple of weeks. I tried some cleaners and they didn't seem to work. Finally bit the bullet and went to buy a new catalytic converter. Turning on the car while leaving the parts warehouse the CEL was gone! It was so surreal I had to laugh for a moment. I ran the OBD reader I have to find out that the catalytic converter was performing the same, but the parameters the computer allowed for an acceptable converter output was widened somehow so now my converter is operating in acceptable ranges. I went and got car inspected right after and it passed emissions! So do I need to put in the new converter or can I return it and get $500+ back?
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2022, 10:31 AM
Post #2 of 8
(1137 views)
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Re: P0420 Code vanishes
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No, that is not true. Unless the dealer reprogrammed the computer, changing the converter didn't change any parameters.
Please include the year, make, model and engine size in every question.
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MoodMan
Novice
Jun 2, 2022, 10:49 AM
Post #3 of 8
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Re: P0420 Code vanishes
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It's a 2.4L 2013 Buick Encore. I did not put the new converter in yet. The CEL light went away, I checked the code reader and yes the parameters changed. The converter was performing the same but somehow the parameters changed. Wish I could upload a pic to prove it
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2022, 10:55 AM
Post #4 of 8
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Re: P0420 Code vanishes
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The parameters for setting the code are not even visible and are built into the programming of the PCM. They cannot change.
It's not just a simple bracket. In order to set that code the rear 0/2 has to mirror the front 0/2 for a specific period of time along with numerous other requirements.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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MoodMan
Novice
Jun 2, 2022, 11:04 AM
Post #5 of 8
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Re: P0420 Code vanishes
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Note the parameters listed under Catalyst Monitor Bank 1.
These readings were taken with OBDLink about a week apart.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 2, 2022, 11:08 AM
Post #6 of 8
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Re: P0420 Code vanishes
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Ignore all that stuff.
You are looking at raw, unprocessed voltages of a single 0/2 downstream sensor. That info has no bearing on whether it sets a P0420 code. The computer looks at an entirety of data to determine if that code it set.
The high and low limits there are just numbers the code reader manufacturer programmed in. It tells you nothing.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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MoodMan
Novice
Jun 2, 2022, 11:32 AM
Post #7 of 8
(1110 views)
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Re: P0420 Code vanishes
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So why would the code go away suddenly after 2 weeks? Should I be worried about it coming back?
I appreciate your help
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Hammer Time
Ultimate Carjunky
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Jun 2, 2022, 11:37 AM
Post #8 of 8
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Re: P0420 Code vanishes
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I'm going to delete your previous pictures as they are too large and messing up the thread.
Yes, it will be back eventually. It simply isn't meeting all the requirements for the time being.
DTC P0420
- Catalyst System Low Efficiency
Circuit/System Description
A 3-way catalytic converter controls emissions of hydrocarbons, Carbon Monoxide (CO) and Nitrogen Oxide (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and Carbon Dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The ECM monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the 3-way catalytic converter. The HO2S 2 produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by allowing the catalyst to heat, then wait for a stabilization period while the engine is idling. The ECM then adds and removes fuel while monitoring the HO2S 2. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the response of the HO2S 1, which is located before the 3-way catalytic converter. When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold.
Conditions for Running the DTC
* DTC P0016, P0017, P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P013A, P013B, P013E, P013F, P0140, P0141, P015A, P015B, P16F3, P0171, P0172, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0502, P0503, P0506, P0507, P0606, P0697, P06A3, P2101, P2122, P2123, P2127, P2128, P2135, P2138, P2270 or P2271 is not set.
* Before the ECM performs the idle test, the vehicle must be driven under the following conditions:
- The engine speed is greater than 1,100 RPM for a minimum of 5 s.
- The vehicle speed is less than 2 km/h (1.24 mph).
- The engine runtime is greater than 120 s.
* The run/crank voltage is greater than 11 V.
* The intake air temperature (IAT) is between -20 to +250°C (-4 to +482°F).
* The engine coolant temperature (ECT) is between 40-140°C (104-284°F).
* The engine has been idling less than 50 s.
* The short term fuel trim is between -20 to +30.
* The barometric pressure (BARO) is greater than 70 kPa.
* The intake mass air flow (MAF) is between 1.50-7.00 g/s.
* The engine is operating in closed loop.
* The calculated catalyst temperature is between 550-950°C (1,022-1,742°F).
* The automatic transmission is in drive range.
* This diagnostic attempts one test during each valid idle period once the above conditions have been met. This diagnostic attempts up to 8 tests during each drive cycle.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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