P0420 Code - Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
The Engine Control Module (ECM) uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency. Common causes include Gas leak from exhaust system, Faulty Three-way Catalyst Converter Bank 1, Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor). Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
- What it means
- P0420 indicates Catalyst System Efficiency Below Threshold Bank 1.
- Common causes
- Common causes include Gas leak from exhaust system, Faulty Three-way Catalyst Converter Bank 1, Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor).
- Severity
- Moderate - service should be scheduled soon.
- Can I drive?
- The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
Code P0420 Description
The first sensor, the air-fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.
In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air-fuel ratio control.
The oxygen storage capacity value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air-fuel ratio to lean or rich levels. If the cycle of the waveform for the heated oxygen sensor is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor and the oxygen storage capacity of the three-way catalytic converter.
The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. If any deterioration has occurred, the ECM illuminates the MIL and stored the DTC.
This system determines the deterioration of the entire catalyst system (including the front and rear catalysts), by using the oxygen storage capacity value of the front catalyst, which is more sensitive than the rear catalyst, as the representative value. Therefore, be sure to replace the front and rear catalysts together when catalyst replacement is necessary.
What are the Possible Causes of the DTC P0420?
- Gas leak from exhaust system
- Faulty Three-way Catalyst Converter Bank 1
- Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor)
- Faulty Heated Oxygen Sensor Bank 1 (Sensor 2 or Rear Sensor or Downstream Sensor)
- Faulty Fuel Injector(s)
How to Fix the DTC P0420?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
User Submitted Video
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0420 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Information for Specific Makes
- P0420 Acura — Catalyst System Efficiency Below Threshold
- P0420 Audi — Catalyst System Efficiency Below Threshold Bank 1
- P0420 BMW — Catalytic Converter Conversion
- P0420 Buick — Catalyst System Low Efficiency Bank 1
- P0420 Cadillac — Catalyst System Low Efficiency Bank 1
- P0420 Chevrolet — Catalyst System Low Efficiency Bank 1
- P0420 Chrysler — Catalyst System Efficiency Bank 1
- P0420 Dodge — Catalyst System Efficiency Bank 1
- P0420 Ford — Catalyst System Efficiency Below Threshold Bank 1
- P0420 GMC — Catalyst System Low Efficiency Bank 1
- P0420 Honda — Catalyst System Efficiency Below Threshold
- P0420 Hyundai — Warm Up Catalyst Efficiency Below Threshold Bank 1
- P0420 Infiniti — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Isuzu — Catalyst System Low Efficiency Bank 1
- P0420 Jaguar — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Jeep — Catalyst System Efficiency Bank 1
- P0420 KIA — Warm Up Catalyst Efficiency Below Threshold Bank 1
- P0420 Lexus — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Mazda — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Mercedes-Benz — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Mercury — Catalyst System Efficiency Below Threshold Bank 1
- P0420 MINI — Catalytic Converter Conversion
- P0420 Mitsubishi — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Nissan — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Pontiac — Catalyst System Low Efficiency Bank 1
- P0420 Saturn — Catalyst System Low Efficiency Bank 1
- P0420 Scion — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Subaru — Catalyst System Efficiency Below Threshold
- P0420 Toyota — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Volkswagen — Catalyst System Efficiency Below Threshold Bank 1
- P0420 Volvo — Catalyst System Efficiency Below Threshold Bank 1
Frequently Asked Questions about P0420 Code
1. What are common symptoms of OBDII code P0420?
Common symptoms of P0420 include a check engine light illuminated on the dashboard, reduced fuel efficiency, and a lack of engine power.
2. What does the OBDII code P0420 indicate?
P0420 indicates that the catalytic converter in Bank 1 of the engine is not operating at the expected efficiency level.
3. What are the possible causes of OBDII code P0420?
Potential causes of P0420 include a faulty catalytic converter, oxygen sensor issues, exhaust leaks, engine misfires, or fuel system problems.
4. Can a bad O2 sensor trigger code P0420?
Yes, a malfunctioning oxygen sensor, particularly the upstream sensor in Bank 1, can contribute to triggering code P0420.
5. How can I diagnose the cause of OBDII code P0420?
Diagnosing P0420 may involve inspecting the catalytic converter, checking oxygen sensor readings, examining exhaust system components for leaks, and testing for engine misfires.
6. Is it safe to continue driving with OBDII code P0420?
While driving with code P0420 may not cause immediate harm to your vehicle, it is essential to address the underlying issue promptly to prevent further damage and maintain vehicle performance.
7. Can I reset the check engine light after fixing OBDII code P0420?
After repairing the issue causing P0420, you can reset the check engine light using an OBDII scanner or by disconnecting the car battery for a few minutes.
8. Do I need to replace the catalytic converter for code P0420?
In some cases, replacing the catalytic converter may be necessary to resolve P0420, especially if the converter is damaged or not functioning correctly.
9. Are there any DIY repair tips for OBDII code P0420?
DIY repair tips for P0420 include checking for exhaust leaks, ensuring proper oxygen sensor function, and performing regular maintenance to prevent future catalytic converter issues.
10. How can I prevent OBDII code P0420 from recurring?
To prevent code P0420 from coming back, maintain your vehicle according to the manufacturer's recommendations, address engine performance issues promptly, and use quality fuel to reduce the likelihood of catalytic converter problems.
Discuss the causes and fixes for P0420 OBDII Code
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Use gas conditioner, fuel injector cleaner then fill up with shell high test gas. Now buy a inexpensive diagnostic tool and clear the code. Drive the required driving cycle (not sure exactly what that is), and for me there where no codes and the engine light went out. So stop those blood suckers from robbing you, and troubleshoot yourself. The $79.95 I spent for a diagnostic tool from sears that gives codes and definitions, payed for itself and I figure I saved over 1K.
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No I have not replaced any parts but I've had O2 sensor errors before. The wiring connection was durty so when wet I'd get the error and when dry it would clear. I'll try fuel conditioner. I have gotten an error on my 2008 suburban and it says plugged injector, so I put in Sea Foam and it clears up. I'll try the Sea Foam on my 1998 PU and see if it clears the P0420 code.
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Performance Muffler in Norman OK reads and clears these lights for free.
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I have replaced all o2 sensors and even the catalytic converter when i recieved the p0420 and 430, and that didnt fix error code. Come to find out all i needed to do was a basic tune up, that consisted of changing spark plugs and wires, and really didnt need to change the wires. The problem was, a couple of spark plugs, were faulty. The gaps on the plugs had closed up to where the plugs were getting very little to no spark. So if u have never changed your plugs or even did a tune up i would start there. I paid for a valuable lesson. I work on my own vehicles.
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I have the same codes coming up what kind of car do you have that you changed the spark plugs on i want to try to do the same thing thanks
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recently had this code in a 2002 gmc sonoma 4.3L auto 4x2. but mine was a sure thing. the converter was rattling. the packing used inside the converters holds the brick in place. once it broke down it lets air around the brick and the 02 sensor is sensitive enough to detect it. cut the converter off and sure enough the brick is laying there and you can move it around. $60 eastern catalytic universal converter 83166 on ebay. if you can weld.... if not you have to buy the whole y pipes kit which is over $300 and risk breaking the manifold studs removing them. I'd rather weld a cat in than mess with all that. anyone with a rattle in the cat it's a sure thing that it's bad.
btw, 139k miles and the brick was spotless clean. converters don't just plug up if there is no other issues with the motor...all you folks with "plugged" converters are running the vehicles with other issues and never fixing them.also if you replace a converter they require a "break in". you need to run the engine idle for 5 mins. then increase the rpm to 2500 for 2 min. let engine cool completely. then you can drive it.
hope this helps anyone in the future...
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Fixed this on my Tacoma by sealing the leaking flange between the catalytic converter and the pipe (that holds the #2 O2 sensor) that goes to the muffler. Driven over 1000 miles, no troubles. Before I looked, I thought it was going to be an expensive part, but it turned out to be less than $30 for a high grade gasket material and some liquid gasket stuff made for mufflers.
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2005 hilux P0420 code
i have replaced the oxygen sensor x2 and the cat. converter but the cat converter is from a new land cruiser and im still getting the same code needs some help please.... thanks -
It should work, but how do you know the catalytic converter was good? also what gas octane are you using? Low octane gas can also cause the P0420 code.
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You can't be more specific on sensors. None of your info makes sense. So is it bank 1 sensor 1 or bank 1 sensor 2 that needs to be changed for this code??? White sleeve or black???
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The problem is usually the catalytic converter and not the sensors. The color of the sleeves depends on the make, model and year, and some makes have the same color for both sensor. Sleeve color is not an accurate way to describe a sensor.
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Hi guys,
I have a 2006 kia rio and have had this code come up,ive been advised of the several issues that could be causing this and i can say that im really not happy to have to pay 1,000+ to have the catalytic converter replaced. Do you have any info on what other likely or common issues there are with this model car to this code just so that i can try the cheaper alternatives before having to pay out money i really dont have.
Thanks in advance. -
I have an 08 Caddilac CTS with the 3.6L DOHC motor. I had a code for cam timing that required the replacement of the timing chains. About 100 miles after I got it out of the shop for that I now have P0420. Could the bad cam timing have anything to do with a bad cat. converter??
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It's possible, depends how long did you drove your vehicle with the timing problem. How is the engine performance now with the new timing chains?
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I drove it a couple of months before it was confirmed. The performance degraded slowly over the life of the car and it wasn't until the timing chains were replaced that I discovered how much it had degraded. After the chain replacement and the P0420 code appeared I drove the car approx.300 miles and when I got in it this morning the check engine light was off and the code had disappeared. Thank you for the response.
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Help. I have a 2013 Dogde Jouney. My daughter made too tight of a turn and hit the back passenger tire on curb, now my check engine light is on and I have the P0420 code.
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I have a 2002 Nissan sentra and had a po40 code.I had the cat. cleaned out, and now I can start the car and drive it until it warms up cut it off,then start it up and try to drive it will run but will not shift. I can then cut it off start it up and it will run OK.
Please help
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Problems with the catalytic converter should not cause any shifting issues, it's possible that you may have two different problem, one with the catalytic converter and with the transmission.
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