P0420: Catalyst System Efficiency Below Threshold (Bank 1)
Short answer: P0420 means “Catalyst System Efficiency Below Threshold (Bank 1)”. It is a standard OBD-II code, so the basic meaning is the same on every car. Below is what it means on each of the 7 cars we cover, with a link to the full page for each car.
Standard OBD-II code Same meaning on all cars (SAE J2012).
P0420 on each car
| Car | Meaning on this car | Confidence |
|---|---|---|
| Toyota Passo (1st gen) | Catalyst System Efficiency Below Threshold (Bank 1) | low |
| Toyota Vitz (1st gen) | Catalytic converter efficiency below threshold | medium |
| Toyota Corolla (11th gen, E170) | Catalyst System Efficiency Below Threshold (Bank 1) | medium |
| Toyota Corolla (10th gen, E140) | Catalyst System Efficiency Below Threshold (Bank 1) | medium |
| Honda City (5th gen, GM2) | Catalyst System Efficiency Below Threshold (Bank 1) | medium |
| Honda Civic (10th gen, FC) | Catalyst System Efficiency Below Threshold (Bank 1) | medium |
| Suzuki Wagon R (Pakistan, K10B) | Catalyst System Efficiency Below Threshold (Bank 1) | medium |
Symptoms
- Check engine light on
- Symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in…
Likely causes
- A code
- P0420
- Has happened
- Leaded fuel was used where unleaded was called for (unlikely)
- A damaged or failed oxygen / O2 sensor
- Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
- The engine coolant temperature sensor is not working properly
What to check, in order
- Read the code and live data with an OBD-II scanner
- Look for exhaust or vacuum leaks and check the wiring of the sensor or valve
- Test the part before replacing it
- Fix the cause, clear the code and test-drive
Causes and checks above are the general meaning. The exact test steps and values differ by car: open your car’s page.