P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1)
CodePage.genericDisclaimer
Qu'est-ce que cela signifie ?
Code P0420 indicates the catalytic converter on Bank 1 is not operating at maximum efficiency. The PCM monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. When the downstream sensor mimics the upstream sensor's switching pattern, it means the catalyst is no longer cleaning exhaust gases effectively.
Diagnostic system: Catalyst and oxygen sensor monitor
On a Lexus Rx, the P0420 code should be diagnosed as part of the catalyst and oxygen sensor monitor group. Related codes and live data from this same system can change the repair priority, so avoid replacing parts from the code name alone.
Most Common Causes for Lexus Rx
- Catalyseur défaillant ou obstrué
- Sonde lambda (O2) défectueuse
- Fuite d'échappement avant la sonde lambda
- Bougies d'allumage usées ou encrassées
- Injecteur de carburant obstrué ou défectueux
- Le logiciel du PCM/ECM doit être mis à jour (TSB)
Symptômes à surveiller
- Le voyant moteur est allumé
- Odeur d'œuf pourri (soufre) à l'échappement
- Échec au contrôle des émissions
- Consommation de carburant accrue
- Perte significative de puissance du moteur
CodePage.beforeReplacing
- Inspect for exhaust leaks before the downstream oxygen sensor.
- Compare upstream and downstream O2 sensor live data after the engine is fully warm.
- Check fuel trim and misfire history before replacing the catalytic converter.
- Check for blown fuses, weak battery voltage, and damaged connectors before buying major parts.
Comment Diagnostiquer
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Replacing the catalytic converter before checking exhaust leaks, O2 sensor behavior, fuel trims, and misfire history. Always confirm the fault with freeze-frame data, live data, visual inspection, and circuit checks before spending money on parts.
CodePage.faq
Can I drive with the P0420 code?
If the check engine light is solid, you can usually drive to a safe location or mechanic. If the light is flashing, pull over immediately to prevent catastrophic engine or catalytic converter damage.
Will the P0420 code clear itself?
Once the underlying problem is fixed, the engine computer will run its self-checks. If it passes over several drive cycles, the light will turn off automatically. You can also clear it immediately using an OBD2 scanner.
Will this code fail an emissions test?
Yes. If the Check Engine Light is on due to the P0420 code, your Lexus will automatically fail an OBD2 plug-in emissions or smog test.
What should I check first for P0420?
Inspect for exhaust leaks before the downstream oxygen sensor. Compare upstream and downstream O2 sensor live data after the engine is fully warm. Check fuel trim and misfire history before replacing the catalytic converter.
Join the Discussion
Estimation de réparation
Exhaust leak check, wiring repair, or sensor connector repair
Catalytic converter replacement after verified failed catalyst monitor
Comprend les pièces et la main-d'œuvre. Peut varier selon l'emplacement.
Cheap fixes are usually leaks, wiring, or sensors; converter replacement is the expensive last step after tests confirm low catalyst efficiency.
Difficulté de réparation (DIY)
Can usually be performed at home with basic hand tools.