Fault code P0420 is called “Catalyst System Efficiency Below Threshold (Bank 1)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0420
This diagnostic trouble code (DTC) is a generic transmission code. Error P0420 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.
The catalytic converter is a part of the exhaust system that looks like a muffler. But its operation is very different from that of a muffler. The catalytic converter works by reducing exhaust emissions.
There is an oxygen sensor on the neutralizer in the front and rear. When the vehicle is warmed up and operating in closed circuit mode. The oxygen sensor O₂ reading in front of it should fluctuate. The reading of the oxygen sensor O₂ behind it should be quite stable.
Normally, code P0420 is set and the check engine light (Check Engine) is illuminated if the readings of the two sensors are identical. Oxygen sensors O₂ are also called lambda probes. The error also indicates that the catalytic converter is not working as efficiently as it should (according to specifications).
Catalytic converters are not usually a “wear-resistant” product, meaning they need to be replaced periodically. If they fail, you need to look for the specific cause that caused them to fail.
Many nuances can lead to failure of O₂ sensors or catalysts. Before replacing parts, you need to make sure that all problems are fixed. Otherwise, they may reappear.
Check with an OBD-2 scanner for other errors and correct them, as they may be the cause of the P0420 malfunction. Make sure your vehicle is not burning oil and has no other problems.
Blue smoke means oil entering the combustion chamber. White, is water or antifreeze. Gray or black, means a saturated mixture.
Symptoms of vehicle malfunctions
The main signal that an error P0420 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- Other related fault codes may also be present.
- The engine stalls or starts poorly.
- Floating revolutions, as well as attempts to stall at idle.
- Decreased engine power.
- Poor acceleration.
- Increased fuel consumption.
- Sometimes there may be no symptoms, despite the stored fault code.
This error is considered moderate if there are no symptoms. However, if symptoms are present, the cause of error P0420 must be corrected as soon as possible. Ignoring it can cause serious damage to the catalytic converter.
Factors that can cause this error code
The error code P0420 can mean that one or more of the following problems have occurred:
- Ethylated fuel was used where unleaded fuel was required (unlikely).
- Damaged or faulty oxygen sensor (O₂).
- Damaged or faulty oxygen sensor wiring (HO₂S).
- Engine coolant temperature sensor is not working properly.
- Damaged or leaking exhaust manifold, catalytic converter, muffler, exhaust pipe.
- Faulty or poorly functioning catalytic converter (probably).
- Delayed ignition timing.
- Oxygen sensors in front and rear of catalytic converter are reporting too similar readings.
- Leaking fuel injector or high fuel pressure.
- Cylinder misfire.
- Contamination by petroleum products.
How to fix or reset OBD-2 code P0420
Some suggested steps for troubleshooting and fix the error code P0420:
- Read all the error codes stored in the vehicle’s PCM memory with an OBD-II scan tool.
- Check the operation of the oxygen sensor O₂ located behind the catalytic converter (at the exhaust outlet). Voltage reading of this sensor should be stable.
- Diagnose other error codes that may have caused code P0420.
- Troubleshoot the engine cylinder ignition timing and fuel system malfunctions.
- Check the oxygen sensor installed behind the catalytic converter (at the exhaust outlet) for wear and damage.
- Test-drive the vehicle to check the oxygen sensor.
- Replace the defective catalytic converter and update the PCM software if necessary.
Diagnose and repair of problems
If there are no additional errors, clear fault code P0420 and perform a short test drive. To allow the PCM to go into closed loop mode, then scan the system again and see if the code has returned.
If the code is found, check the oxygen sensors to make sure they are working properly. Compare the displayed output signals with the values given in the manual.
Read the inlet temperature reading of the transducer and then the outlet temperature reading. The difference between the input and output temperatures should be about 99°F. If the temperature difference approaches 200°F or reaches 500°F. The catalytic converter is most likely damaged.
Remove the front oxygen sensor and screw a gauge into the exhaust system instead. Start the engine and let it idle, observing the back pressure of the exhaust gases. Compare the reading with the maximum allowable value indicated in the manual. Do the same with the lower gauge.
If no excessive catalytic converter temperatures are detected and the exhaust back pressure is within acceptable limits. Almost certainly the converter has failed due to prolonged use. This leads to the error P0420.
Replacing the catalytic converter requires equipment and skill. Thus, if a faulty catalytic converter is diagnosed. The best option is to send the vehicle to a specialized workshop.
On which vehicles does this problem occur most frequently
Fault code P0420 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Acura (MDX)
- Audi (A4, A6, Q5, Q7)
- BMW (X5)
- Cadillac (SRX)
- Chery (Tiggo)
- Chevrolet (Aveo, Captiva, Cruze, Epica, Lacetti, Lanos, Spark, TrailBlazer)
- Chrysler (300C, PT Cruiser, Pacifica, Sebring, Voyager)
- Citroen (Berlingo, C4, C5, Xsara Picasso)
- Daewoo (Gentra, Matiz, Nexia)
- Dodge (Caliber, Caravan, Stratus)
- Fiat (Doblo)
- Ford (C-Max, Explorer, Fiesta, Focus, Fusion, Galaxy, Maverick, Mondeo)
- Geely (Emgrand, MK)
- Honda (Accord, CR-V, Civic, Fit, Pilot)
- Hyundai (Accent, Elantra, Getz, Santa Fe, Solaris, Sonata, i30, ix35, ix55)
- Infiniti (FX35, QX56)
- Jeep (Compass, Grand Cherokee, Liberty)
- Kia (Carens, Ceed, Cerato, Magentis, Optima, Picanto, Rio, Sorento, Spectra, Sportage)
- Lexus (GS300, GX470, LS430, LX470, RX300, RX330)
- Lifan (X60)
- Mazda (3, 6)
- Mercedes-Benz (W204)
- Mitsubishi (Lancer, Outlander)
- Nissan (Almera, Micra, Murano, Note, Pathfinder, Patrol, Primera, Qashqai, Sentra, Teana, Tiida, X-Trail)
- Opel (Antara, Astra, Corsa, Insignia, Meriva, Vectra, Zafira)
- Peugeot (107, 206, 207, 3008, 301, 307, 308, 406, 407, 408, Partner)
- Pontiac (Vibe)
- Renault (Duster, Fluence, Kangoo, Logan, Megane, Sandero, Scenic)
- Skoda (Fabia, Octavia)
- Subaru (Forester, Impreza, Legacy, Outback, Tribeca)
- Suzuki (Grand Vitara, Ignis, Liana, SX4, Swift)
- Toyota (Avensis, Camry, Celica, Corolla, Highlander, Land Cruiser, Matrix, Prado, Prius, RAV4, Verso, Yaris)
- Volkswagen (Bora, Caddy, Golf, Jetta, Passat, Polo, Tiguan, Touareg)
- Volvo (S40, S60, S80, V40, XC70, XC90)
- Vortex (Estina, Tingo)
- GAZelle (Business)
- LADA (Largus)
- UAZ (Buhanka, Hanter, Patriot)
- Volga (Siber)
- ZAZ (Chance)
Fault code P0420 can sometimes be found with other errors. The most common are the following: P0106, P0131, P0133, P0151, P0171, P0172, P0174, P0300, P0430, P0442, P0455, P0573, P069E.