emissions testing/issues with P0420

[John105]

I get the feeling I will be in the vast minority being concerned with a P0420.

12/25/21 code appeared, reset

We can inspect current month, and next two, in PA. So since the car had October 2022 stickers, waited until August 2022, inspected the car, got October 2023 stickers.

Sure enough, P0420 again September 2023! Lucky we inspected already.

Why, well, with this GM if the codes erased, its I/M will be ready in around 100 miles, EXCEPT FOR EVAP, which takes 700-1100 miles.

Since 9/22, the car has never gotten itself into a I/M ready before the code came back.

My brother and family came to town 4/28 for the weekend, and we drove all around, and the tank was much lower than we normally let it get.

Last week, I found the car was I/M yes to all.

Went to indie garage, asked for an inspection, and of course, they wanted to know why on May 19, when it's good through October.

I explained the P0420 blah blah blah. They said ok. So if it costs $42 for 12 mos, I figure I am throwing away 5 months, but buying time to deal with the issue (a friend paid the dealer $1800 for same code, same car, in 2019).

When picking up the car, to my surprise, they put 7/24 stickers on it. They do have the prerogative to do so, because today, May, Jun, Jul stickers can be issued in May. So we have 13 1/2 months to deal with the issue.

Car being a 2011, I told them Walker cat if it needs replacement, being ~ $300. We are allowed to install Fed certified cats on Calif cars in PA. Not true in CA, ME, CO, and NY.

I know my cousin also has P0420 on his 2004 M5, and he resets the codes, drives until ready, and parks until emissions testing, in MA.

Emissions is a pita and I feel it often spells the end of a vehicle in states with testing.

Do you have any P0420 or P0430 stories to tell, and how you dealt or deal with them? They lower our overall quality of life

 

[slacktide_bitog]

Eastern cats are also good, and they are made in PA

Another option is to sell the car to someone in a non-emissions county

 

[hrv]

O2 sensor spacer.

They do work but some inspection sites look underneath with a mirror...so they might or might not see the spacer....

 

[atikovi]

They do work but some inspection sites look underneath with a mirror...so they might or might not see the spacer....

Get the non-stainless steel version that will develop a patina like the rest of the exhaust and look factory, or custom make a heat shield looking thing to cover it enough that they can't see it.

 

[2strokeNorthstar]

In CA it's allowed to be not ready if all others are good. If you know is going to trigger, reset codes, fill tank and don't let it get below 3/4 tank while all other monitors test/ready. Go get a smog test then blow it off for another 2 years.

My F150 had a fuel sender issue where is kind of worked but it wasn't exactly accurate. The Evap monitor went years, probably 6-8, without being ready because the tank Readings were never stable enough to run the test. The fuel sender finally got bad enough to no longer work. I got a new pump assembly installed and monitor ran within a few days.

*sorry just realized AFTER TYPING all this that I am talking about the wrong code.

 

[supton]

Somehow I have avoided them. Go figure, my two that no longer have to pass emissions, knock on wood, aren’t tossing codes. But it sure was a concern when I had my VW as it liked to toss one at times.

 

[SC Maintenance]

Smart move on your part regarding getting emissions early.

I have read Cataclean will fix the code for 100 miles or so - might be worth a try next time in your case. In theory the code should reset itself after enough cycles without having to clear all codes and readiness monitors - I think?

I have had P0420 and P0430 on my Nissan's. Replaced cats and they went away. Specific to my Nissan's - I don't see how - if its the only code and your fuel trims are good - can be anything other than either a bad cat, bad secondary 02 sensor or a exhaust leak. Those codes - again on Nissan and per the control algorithm - are very specific to the secondary 02 sensors not seeing enough "cleaning" after the cat. If you had something like a MAF sensor or vacuum leak / sticking injector, I would think you would see that in fuel trims and / or other codes, like rich or lean codes. Again, this might be Nissan Specific, or I could be mis-reading my FSM.

We have no emissions checks but I don't like codes. I went with Easterns and they have been fine, but the fit was terrible and I could only seal the system with some special mopar gaskets I found, not to mention the one Eastern is square rather than round and has only 1/8" clearance if that from the cross member which it hits on some bumps. THe OEM one had like an inch.

 

[John105]

Smart move on your part regarding getting emissions early.

I have read Cataclean will fix the code for 100 miles or so - might be worth a try next time in your case. In theory the code should reset itself after enough cycles without having to clear all codes and readiness monitors - I think?

I have had P0420 and P0430 on my Nissan's. Replaced cats and they went away. Specific to my Nissan's - I don't see how - if its the only code and your fuel trims are good - can be anything other than either a bad cat, bad secondary 02 sensor or a exhaust leak. Those codes - again on Nissan and per the control algorithm - are very specific to the secondary 02 sensors not seeing enough "cleaning" after the cat. If you had something like a MAF sensor or vacuum leak / sticking injector, I would think you would see that in fuel trims and / or other codes, like rich or lean codes. Again, this might be Nissan Specific, or I could be mis-reading my FSM.

We have no emissions checks but I don't like codes. I went with Easterns and they have been fine, but the fit was terrible and I could only seal the system with some special mopar gaskets I found, not to mention the one Eastern is square rather than round and has only 1/8" clearance if that from the cross member which it hits on some bumps. THe OEM one had like an inch.

The indie shop said they would like to try 4 new 02 sensors first, before assuming a CAT is needed. I did buy all 4 OEM (Bosch is OEM to GM in this case), they were only $50'ish so I'm out $200. But I don't even want to have them installed until I have to. Problem with older vehicles is emissions is just one thing, and not cheap. Pay to correct emissions, and other things could go as well....

The internet is flooded with people who had the dealer replace and all was good. Never found anyone on this car where they cleaned the CAT--what if it can be removed and cleaned? Although it's the rear bank and this is a crossover AWD SUV. So much has to come out for certain jobs...

 

[walterjay]

I have used Cataclean and passed emmisions with a weak converter.

 

[John105]

btw this is a copy/paste of how to get our car into a ready state

I think it's a heck of a lot easier for a coach to have his team with the Stanley Cup!

Inspection/Maintenance (I/M) Complete System Set Procedure
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provide an overview of each diagnostic category.

Description
The purpose of the Inspection/Maintenance (I/M) complete system set procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics and complete the drive cycles for those particular diagnostics. When all I/M monitored diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform the Inspection/Maintenance (I/M) Complete System Set Procedure if any I/M System Status indicators are set to NO.

I/M Data List
To determine if the I/M readiness diagnostic tests can be run during this ignition cycle, use a scan tool to observe the I/M monitor-enabled parameters in the I/M Data List.

Conditions for Meeting a Cold Start
• The ignition voltage is between 11-18 volts.
• The barometric pressure (BARO) is more than 75 kPa.
• The start-up engine coolant temperature (ECT) is between 4-30°C (39-86°F).
• The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
• The difference between the IAT and the ECT is less than or equal to 6°C (10.8°F)
• The ambient air temperature is between 4-30°C (39-86°F).
• Fuel level is between 15-85 percent
• Without RPO LMG--The fuel alcohol content is less than 15 percent.
• With RPO LMG--The fuel alcohol content is less than 87 percent.

Circuit/System Verification
Review the Inspection/Maintenance (I/M) System Status indicators with a scan tool. All I/M System Status indicators should report YES.

Inspection/Maintenance (I/M) System Set Procedure
Important: Whenever the ignition is turned ON, an ignition positive voltage is supplied to the heated oxygen sensor (HO2S) heaters. After verifying the enable criteria, turn OFF the ignition for approximately 5 minutes to allow the sensors to cool before continuing with the test. Once the engine is started, do NOT turn the engine OFF for the remaining portion of the set procedure.

1. Ensure that the vehicle meets the conditions for a cold start listed above.
   ⇒ If the evaporative emission (EVAP) I/M System Status indicator displays NO, perform the EVAP Service bay test if available.
   ⇒ If the EVAP Service bay test is NOT available, it may take up to 6 drive cycles, up to 17 hours between drive cycles, for the EVAP I/M System Status indicator to transition to YES.
   ⇒ If the O2S Heater System Status indicator displays NO, ensure that the ignition has been turned OFF for at least 10 hours.
2. Set the vehicle parking brake and ensure the vehicle is in the park for automatic transmission or neutral for manual transmission.
3. Turn OFF all accessories, HVAC system, and other electrical loads, including aftermarket/add-on equipment, etc.
4. Start and idle the engine for at least 2 minutes until 65°C (149°F) is achieved.
5. Run the engine for 6.5 minutes within the following conditions:
   • MAF parameter between 4-30 g/s
   • Engine speed steady between 1000-3000 RPM
6. Return the engine to idle for 1 minute.
7. Apply and hold the brake pedal, and shift to Drive for automatic, or apply the clutch pedal for manual and operate the vehicle within the following conditions for 2 minutes:
   • Depress the accelerator pedal until the TP Sensor angle is more than 2 percent.
   • MAF signal between 15-30 g/s
   • RPM steady between 1200-2000 RPM
   
   Important: Do NOT touch the accelerator pedal during the idle period. A change in TP Sensor angle or an increase in engine speed may invalidate this portion of the test.
8. Release the accelerator pedal and shift the vehicle to Park for automatic or Neutral and release the clutch pedal for manual, and allow the engine to idle for 2 minutes.
9. Quickly depress the accelerator pedal until TP Sensor Angle is more than 8 percent and return to idle. Repeat 3 times.
10. Allow the engine to idle for at least 2 minutes.
11. Release the parking brake and drive the vehicle at 24 km/h (15 mph) or slower for 2 minutes.
12. Continue to drive the vehicle for at least 5.5 miles between 45-112 km/h (28-70 mph), with the vehicle reaching at least 80 km/h (50 mph).
13. Release the accelerator pedal for at least 2 seconds. This will allow the vehicle to enter the decel fuel cut-off.
14. Depress the accelerator pedal until the TP Sensor angle is increased by 3-20 percent, and maintain a safe speed for 1 minute.
15. Safely stop the vehicle, with the engine in drive for automatic or in neutral with the clutch pedal depressed and parking brake applied for manual, idle for 2 minutes.
16. Shift to Park for automatic and apply the parking brake, or neutral and release the clutch pedal for manual.
    
    Important: Do NOT disturb the vehicle or turn ON the ignition until told to do so. Disturbing the vehicle may invalidate this portion of the test.
    
17. Turn OFF the ignition and exit the vehicle. Do NOT disturb the vehicle for 45 minutes.
18. Observe the Inspection/Maintenance (I/M) System Status with a scan tool. All of the I/M System Status indicators should display YES.
    
    ⇒ If the EVAP I/M System Status indicator displays NO turn OFF the ignition for 17 hours, ensure that the vehicle meets the conditions for a cold start, and repeat steps 12-18 six more times or until the EVAP I/M System Status indicator transitions to YES. If the indicator continues to display NO, refer to the Inspection/Maintenance (I/M) System DTC Table to identify the DTCs that did not run. Follow the Conditions for Running the DTC in order to set the EVAP I/M System Status indicator
    
    ⇒ If any of the I/M System Status indicators display NO, refer to the Inspection/Maintenance (I/M) System DTC Table for the indicator which did not display YES. The I/M System DTC Table identifies the DTCs associated with each I/M System Status Indicator. Follow the Conditions for Running the DTC in order to set the associated status indicator.

 

[John105]

And the section specific to EVAP, which seriously, taking 700-1100 miles really makes life hard

• Continue to drive the vehicle for at least 5.5 miles between 45-112 km/h (28-70 mph), with the vehicle reaching at least 80 km/h (50 mph).
• Release the accelerator pedal for at least 2 seconds. This will allow the vehicle to enter the decel fuel cut-off.
• Depress the accelerator pedal until the TP Sensor angle is increased by 3-20 percent, and maintain a safe speed for 1 minute.
• Safely stop the vehicle, with the engine in drive for automatic or in neutral with the clutch pedal depressed and parking brake applied for manual, idle for 2 minutes.
• Shift to Park for automatic and apply the parking brake, or neutral and release the clutch pedal for manual.
  
  Important: Do NOT disturb the vehicle or turn ON the ignition until told to do so. Disturbing the vehicle may cause the vehicle to lose concentration and become forgetful and irritable.
• Turn OFF the ignition and exit the vehicle. Do NOT disturb the vehicle for 45 minutes.
• Observe the Inspection/Maintenance (I/M) System Status with a scan tool. All of the I/M System Status indicators should display YES.
  
  ⇒ If the EVAP I/M System Status indicator displays NO turn OFF the ignition for 17 hours, ensure that the vehicle meets the conditions for a cold start, and repeat steps 12-18 six more times or until the EVAP I/M System Status indicator transitions to YES. If the indicator continues to display NO, refer to the Inspection/Maintenance (I/M) System DTC Table to identify the DTCs that did not run. Follow the Conditions for Running the DTC in order to set the EVAP I/M System Status indicator

 

[SC Maintenance]

The indie shop said they would like to try 4 new 02 sensors first, before assuming a CAT is needed. I did buy all 4 OEM (Bosch is OEM to GM in this case), they were only $50'ish so I'm out $200. But I don't even want to have them installed until I have to. Problem with older vehicles is emissions is just one thing, and not cheap. Pay to correct emissions, and other things could go as well....

The internet is flooded with people who had the dealer replace and all was good. Never found anyone on this car where they cleaned the CAT--what if it can be removed and cleaned? Although it's the rear bank and this is a crossover AWD SUV. So much has to come out for certain jobs...

The primary 02 sensors are usually in front of the first cat. So if that is the case on your vehicle - and your LTFT's are good - +/- 5% - its likely not the primary 02 sensors. Also, P0420 is bank 1, so at best case its the second 02 sensor on bank 1.

I love it when shops say you should replace all 4 sensors for $1500 - when best case is the code points towards a single sensor.

Also, I agree you can't clean a cat for very long, but as I said, cataclean might get you through an inspection if you time it right.

 

[John105]

The primary 02 sensors are usually in front of the first cat. So if that is the case on your vehicle - and your LTFT's are good - +/- 5% - its likely not the primary 02 sensors. Also, P0420 is bank 1, so at best case its the second 02 sensor on bank 1.

I love it when shops say you should replace all 4 sensors for $1500 - when best case is the code points towards a single sensor.

Also, I agree you can't clean a cat for very long, but as I said, cataclean might get you through an inspection if you time it right.

they were willing to charge $150 labor....2 are literally shooting fish in a barrel, the other 2 maybe a little more difficult to access. I totally get there is some setup and tying up a bay and tech (imagine if they charged $40 or $80). I'd be providing the 4 sensors. I do know the official dealer job only changes the 2 sensors on the one bank....

 

[SC Maintenance]

they were willing to charge $150 labor....2 are literally shooting fish in a barrel, the other 2 maybe a little more difficult to access. I totally get there is some setup and tying up a bay and tech (imagine if they charged $40 or $80). I'd be providing the 4 sensors. I do know the official dealer job only changes the 2 sensors on the one bank....

$150 is an excellent price. More a generic comment since the first step for a lot of shops is to replace all 4 sensors. Seen it many times.

 

[dumkid]

i get a p0420 if I don't drive above 40mph for a considerable amount of time (offroading or driving in the city where you can't go very far before the next traffic jam) most of my driving is highway though

 

[2013ecof150]

My dad had a 2000 Corolla that had a weak converter and would throw the 420 code. Tried a few “ fixes in a bottle” and none worked.

The only thing that worked was adding 1 gallon of denatured alcohol to the fuel tank with 1/2 tank or less. I’d reset the code and wait for the monitors to set and he would take it for emissions. Worked every time.

 

[Skippy722]

If it were my car, I’d replace the post catalytic converter O2 sensor and see what happens. First I’d check live data though, if the downstream O2 sensor is mirroring the upstream sensor, it’s probably the cat. If the downstream is reading something crazy (like permanent high/low, or just erratic) it’s probably just the sensor.

 

[John105]

If it were my car, I’d replace the post catalytic converter O2 sensor and see what happens. First I’d check live data though, if the downstream O2 sensor is mirroring the upstream sensor, it’s probably the cat. If the downstream is reading something crazy (like permanent high/low, or just erratic) it’s probably just the sensor.

Can a $100 reader compare the downstream to the upstream? I know it can get live data but not sure how to get that specific. The shop said there was something “off” about the live data, but I did not ask for specifics.

 

[Timmastertech]

Car shouldnt have gotten 7/24 stickers, should have gotten 5/24. Inspection manual states the inspector is to match current expiration if possible or 12 months from current, whichever is longer. No sticker many be issued for longer than 15 months or less than 6 months. Also as a word of caution a walker cat wont keep the light out on most GM SUVs. My experience has been that they fail the catalyst monitor within a few drive cycles. I have eaten a couple of GM cats to warranty out walker cats that failed to keep the light out.

 

[Skippy722]

Can a $100 reader compare the downstream to the upstream? I know it can get live data but not sure how to get that specific. The shop said there was something “off” about the live data, but I did not ask for specifics.

If it can see the O2 sensors and give you the voltages it’s reporting you should be able to compare them. The upstream O2 sensor will bounce between high and low voltage, the downstream sensor should remain relatively stable.