PowertrainP0420
CautionSeverity: Caution - get it checked when you can
Catalyst System Efficiency Below Threshold (Bank 1)
Key terms: Catalytic converter: cleans the exhaust gases · Oxygen sensor: measures oxygen in the exhaust gas · Bank 1: the side of the engine containing cylinder 1 · SAE J2012: the standard generic code list · Powertrain: engine, transmission and emissions
1What it means in plain English
Your catalytic converter is not cleaning the exhaust as well as it should.
2Common causes
- Ageing or failed catalytic converter
- Faulty oxygen sensor behind the converter
- Exhaust leak before the converter
- Engine running rich or misfiring and damaging the converter
- Oil or coolant burning in the exhaust
3Can I drive?
Usually safe to drive. The car will fail an emissions test and fuel economy may be slightly worse. Fixing the underlying cause first is important, so have it diagnosed rather than replacing the converter blindly.
This page gives general information. It is not professional advice. For a definite diagnosis and a repair quote, ask a qualified mechanic to inspect the car.
4Brand data 42
| Brand | Code | Description | System |
|---|---|---|---|
| Ashok Leyland CV | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| BAIC Motor | P0420 | TWC purge efficiency too low Brand | Powertrain |
| Mercedes-Benz | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| BMW | P0420 | Catalytic-converter efficiency too low Brand | Powertrain |
| BYD | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Chery | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Chrysler | P0420 | catalyst system efficiency below threshold bank 1 Brand | Powertrain |
| Daewoo | P0420 | Catalyst System Low Efficiency Brand | Powertrain |
| Daihatsu | P0420 | Catalyst deterioration Brand | Powertrain |
| DFFS | P0420 | Catalytic converter aging Brand | Powertrain |
| DFFX | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| DFXK | P0420 | Catalytic converter degradation Brand | Powertrain |
| EOBD | P0420 | Účinnosť katalyzátora pod prahom bank 1 Brand | Powertrain |
| Ford | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Geely | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| GM | P0420 | Catalyst system low efficiency bank 1 Brand | Powertrain |
| Great Wall | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Hafei | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Holden | P0420 | Catalyst System Low Efficiency Brand | Powertrain |
| Honda | P0420 | 04M Accord DTC67-1 Brand | Powertrain |
| Hyundai | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Isuzu | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Land Rover | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Maserati | P0420 | Catalyst system efficiency below threshold (bank 1) Brand | Powertrain |
| Mazda | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Mitsubishi | P0420 | DPF over loading Brand | Powertrain |
| Nissan | P0420 | TW catalyst system Brand | Powertrain |
| Opel | P0420 | Catalyst system low efficiency bank 1 Brand | Powertrain |
| Perodua | P0420 | Catalyst deterioration Brand | Powertrain |
| Peugeot | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Porsche | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Proton | P0420 | DPF over loading Brand | Powertrain |
| Saab | P0420 | Catalyst system low efficiency bank 1 Brand | Powertrain |
| MG (SAIC) | P0420 | Catalyst General Failure Brand | Powertrain |
| Smart | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Sprinter | P0420 | Catalyst System Efficiency Below Threshold (Bank 1) SAE | Powertrain |
| Subaru | P0420 | Catalyst System Efficiency Below Threshold Brand | Powertrain |
| Suzuki | P0420 | Catalyst System Efficiency Below Threshold (Bank1) Brand | Powertrain |
| SWM Motor | P0420 | Catalytic converter conversion efficiency is low Brand | Powertrain |
| Tata | P0420 | Catalyst Fault Brand | Powertrain |
| Toyota | P0420 | The catalytic converter has low conversion efficiency Brand | Powertrain |
| Volkswagen | P0420 | Catalyst System Brand | Powertrain |
Legend: SAE is the generic J2012 description; Brand is text taken from that manufacturer’s data. Manufacturer rows keep the wording and language of the source data, and non-English text is tagged so screen readers pronounce it correctly.
5Extended variant codes 4
These 7-character codes are manufacturer-specific variants of P0420 and may be reported by some scan tools.
| Brand | Code | Description | System |
|---|---|---|---|
| Mercedes-Benz | P042000 | Der Wirkungsgrad des Katalysators (Zylinderreihe 1) ist nicht ausreichend. Brand | Powertrain |
| Hyundai | P042000 | Oxidation rate of HC during regeration period is below threshold value, ECM sets DTC Brand | Powertrain |
| Porsche | P042000 | Ratio less than 1 = limit value undershot = fault entry Brand | Powertrain |
| SsangYong | P042000 | Faulty catalyst 1 purification rate (1, 2, 3 cylinder lines) Brand | Powertrain |
6Related codes
Browse Pxxx codes or P042xx codes.