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DTC/P0423

P0423: Heated Catalyst Efficiency Below Threshold (Bank 1)

Quick Answer
Moderata GravitàSicuro da guidare (a breve termine)Emissioni

P0423 means the electrically heated catalyst on Bank 1 (an e-cat with an internal resistive heating element used on newer Euro 6 and 6d vehicles to reach light-off temperature within seconds of start) is not converting emissions efficiently. It typically points to either heater element failure, control module wiring issues, or substrate degradation.

Costo di riparazione stimatoDa €105 a €2320+, varia in base al veicolo

Cosa significa P0423?

P0423 means the electrically heated catalyst on Bank 1 (an e-cat with an internal resistive heating element used on newer Euro 6 and 6d vehicles to reach light-off temperature within seconds of start) is not converting emissions efficiently. It typically points to either heater element failure, control module wiring issues, or substrate degradation.

P0423 è un codice diagnostico di guasto relativo a emissioni, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0423 e accende la spia motore.

Quali sono i sintomi di P0423?

Se il tuo veicolo ha attivato P0423, potresti notare uno o più di questi sintomi:

  • Check engine light illuminated, often within the first minute after start
  • Elevated cold-start emissions, visible at idle on a cold morning
  • Slight reduction in fuel economy
  • Possible faint sulfur smell during warm-up
  • Failed emissions test or periodic technical inspection

Cosa causa P0423?

Ecco le cause più comuni di P0423, ordinate in base alla probabilità che siano la causa del problema:

altaFailed e-cat heater element or substrate degradation
mediaFaulty downstream O2 sensor (Bank 1, Sensor 2)
mediaWiring or connector fault to the e-cat heater control module
bassaPrior misfire history damaging the heated brick
bassaOil consumption fouling the catalyst substrate

È sicuro guidare con P0423?

In genere sì, per brevi tragitti. Safe for short-term driving. Heated catalyst codes typically appear on newer Euro 6 and 6d vehicles equipped with electrically heated catalysts (e-cats). Cold-start emissions will be elevated and emissions or periodic technical inspection will not pass with this code active.

Come si diagnostica P0423?

Segui questi passaggi per individuare la causa principale di P0423:

  1. Read freeze frame data and confirm the code triggered shortly after cold start, which is typical of heated catalyst faults
  2. Check for companion heater circuit codes such as P0420, P0422, or manufacturer-specific e-cat heater codes
  3. Measure the resistance of the e-cat heater element using the manufacturer specification (typical values are 0.3 to 2.0 ohms depending on platform)
  4. Inspect the wiring harness and connector to the heater control module for corrosion, broken pins, or water ingress
  5. Graph Bank 1 downstream O2 sensor during cold start. A healthy heated cat stabilises within 20 to 40 seconds

Quanto costa riparare P0423?

I costi di riparazione di P0423 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace heated catalytic converter (Bank 1) €600–€2000 €120–€320 €720–€2320 Professionale
Replace downstream O2 sensor (Bank 1) €60–€180 €60–€130 €120–€310 Moderata
Fix exhaust leak (gasket or flex pipe) €25–€120 €80–€220 €105–€340 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

P0423 su veicoli specifici

P0423 si comporta in modo diverso a seconda del tuo veicolo. Seleziona la tua auto qui sotto per cause specifiche del modello, problemi noti e stime dei costi adeguate:

BMW

P0423 su BMW 3 Series

2019-2024

P0423 on the F30 and G20 BMW 3 Series with B48 turbo-4 and B58 inline-6 engines almost always points to the e-cat assembly fitted from 2019 onward to meet Euro 6d-Temp and 6d-ISC standards. The heater element is integrated into the same housing as the pre-cat, so the whole manifold-cat assembly is replaced as one unit. M3 variants (S58 inline-6) use a similar e-cat setup on Bank 1.

Cosa causa P0423 su una BMW 3 Series?

BMW 3 SeriesIntegrated manifold-and-e-cat assembly forces full unit replacement
BMW 3 SeriesB48 and B58 heater element failure common after 100,000 km

Costo di riparazione di P0423 per BMW 3 Series

Costi stimati per i proprietari di BMW 3 Seriesadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici BMW

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace heated catalytic converter (Bank 1) €840–€2800 €168–€448 €1008–€3248 Professionale
Replace downstream O2 sensor (Bank 1) €84–€252 €84–€182 €168–€434 Moderata
Fix exhaust leak (gasket or flex pipe) €35–€168 €112–€308 €147–€476 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Volkswagen

P0423 su Volkswagen Golf

2019-2024

P0423 on Mk8 Golf TSI models with the EA211 evo and EA888 evo4 engines points to the heated catalyst fitted from 2020 onward for Euro 6d-Full compliance. The e-cat heater element draws around 4 kW briefly at start, and a failing 48V mild-hybrid system can starve it of voltage, mimicking heater failure. Check the 48V battery and DC-DC converter before condemning the cat.

Cosa causa P0423 su una Volkswagen Golf?

Volkswagen GolfWeak 48V mild-hybrid battery starving the e-cat heater of voltage
Volkswagen GolfEA211 evo heater element substrate cracking under thermal cycling

Costo di riparazione di P0423 per Volkswagen Golf

Costi stimati per i proprietari di Volkswagen Golfadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Volkswagen

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace heated catalytic converter (Bank 1) €690–€2300 €138–€368 €828–€2668 Professionale
Replace downstream O2 sensor (Bank 1) €69–€207 €69–€150 €138–€357 Moderata
Fix exhaust leak (gasket or flex pipe) €29–€138 €92–€253 €121–€391 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Audi

P0423 su Audi A6

2019-2024

The C8 Audi A6 with the 3.0 TFSI (EA839) V6 mild-hybrid uses a heated catalyst on Bank 1 to meet Euro 6d emissions during start-stop cycling. P0423 here often correlates with degraded 48V battery condition because every restart pulls high current through the e-cat heater. Always test the 48V system capacity and the DC-DC converter output before replacing the catalyst itself.

Cosa causa P0423 su una Audi A6?

Audi A648V mild-hybrid battery degradation reducing heater current
Audi A6EA839 e-cat heater failure typical between 120,000 and 160,000 km

Costo di riparazione di P0423 per Audi A6

Costi stimati per i proprietari di Audi A6adeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Audi

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace heated catalytic converter (Bank 1) €780–€2600 €156–€416 €936–€3016 Professionale
Replace downstream O2 sensor (Bank 1) €78–€234 €78–€169 €156–€403 Moderata
Fix exhaust leak (gasket or flex pipe) €33–€156 €104–€286 €137–€442 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Mercedes-Benz

P0423 su Mercedes-Benz E-Class

2019-2024

On the W213 facelift E-Class with M256 inline-6 and M264 four-cylinder mild-hybrid powertrains, P0423 typically appears as the integrated starter-generator system ages and supplies less voltage to the e-cat heater on cold starts. Mercedes specifies a 48V system check (battery state of health and ISG output) as a mandatory first step before authorising catalyst replacement under warranty.

Cosa causa P0423 su una Mercedes-Benz E-Class?

Mercedes-Benz E-ClassIntegrated starter-generator output drop reducing heater current
Mercedes-Benz E-ClassM256 and M264 e-cat substrate cracking under repeated start-stop cycling

Costo di riparazione di P0423 per Mercedes-Benz E-Class

Costi stimati per i proprietari di Mercedes-Benz E-Classadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Mercedes-Benz

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Replace heated catalytic converter (Bank 1) €840–€2800 €168–€448 €1008–€3248 Professionale
Replace downstream O2 sensor (Bank 1) €84–€252 €84–€182 €168–€434 Moderata
Fix exhaust leak (gasket or flex pipe) €35–€168 €112–€308 €147–€476 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Questi codici compaiono spesso insieme a P0423 o indicano problemi correlati:

P0420P0421P0422P0424P0433

Domande frequenti su P0423

What is a heated catalyst (e-cat) and why does my car have one?

An electrically heated catalyst contains a resistive element that warms the substrate to its light-off temperature within seconds of engine start, before exhaust heat alone could do it. This dramatically cuts cold-start emissions and is increasingly common on Euro 6d vehicles, hybrids, and high-output performance cars to meet stricter EU emissions limits.

Why is replacing a heated catalyst so much more expensive than a regular one?

Heated catalysts contain an integrated electrical heater element, a high-current connector, and often a dedicated control module or relay. The assembly is more complex than a passive cat and OEM-only in most cases, which is why parts alone range from 600 to 2,000 EUR depending on platform.

Can a wiring problem trigger P0423 instead of the catalyst itself?

Yes. A broken heater wire, corroded pin, or failed heater control module can cause the e-cat to never reach light-off temperature, which the ECU then interprets as catalyst inefficiency. Always perform a heater-circuit resistance check before condemning the converter.

Will an aftermarket non-heated catalyst work as a replacement?

No. The ECU monitors the heater circuit. Replacing a heated cat with a passive cat will trigger both P0423 and heater-circuit codes immediately, and the car will fail emissions testing. Only OEM or OEM-equivalent heated cats should be installed.

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