P0408 means the EGR position sensor 'B' is sending a voltage above its normal operating range. Sensor B exists on engines with dual EGR valves (V6/V8 diesels) or dual feedback sensors. The fault is usually an open signal wire, missing ground, or a sensor that has failed open internally.
P0408 means the EGR position sensor 'B' is sending a voltage above its normal operating range. Sensor B exists on engines with dual EGR valves (V6/V8 diesels) or dual feedback sensors. The fault is usually an open signal wire, missing ground, or a sensor that has failed open internally.
P0408 è un codice diagnostico di guasto relativo a emissioni, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0408 e accende la spia motore.
Se il tuo veicolo ha attivato P0408, potresti notare uno o più di questi sintomi:
Ecco le cause più comuni di P0408, ordinate in base alla probabilità che siano la causa del problema:
In genere sì, per brevi tragitti. Driveable. P0408 affects the secondary EGR position sensor (sensor B), reporting voltage above the expected range. The ECU disables the affected EGR bank or enters limp mode on diesels. Expect rough idle, reduced power, and a failed emissions test.
Segui questi passaggi per individuare la causa principale di P0408:
I costi di riparazione di P0408 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:
Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.
P0408 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:
2014–2024
On the 330d and 335d with B57 inline-6 diesel, P0408 most often points to the low-pressure EGR position sensor (sensor B) failing open. The low-pressure EGR sits behind the DPF, so wiring runs through a heat-stressed area. Connector failures are common around 130,000 km. ISTA or Carly is needed for adaptation reset after the low-pressure EGR is serviced.
Costi stimati per i proprietari di BMW 3 Seriesadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici BMW
Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.
2012–2024
P0408 is rare on Golf TDIs because most EA189/EA288 4-cylinder engines lack a sensor B. When it appears, it usually points to either a market-specific calibration that labels the single sensor as 'B', or to the dual-EGR variant found on some commercial Crafter and Caddy derivatives. VCDS readout confirms which sensor is actually faulted.
Costi stimati per i proprietari di Volkswagen Golfadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Volkswagen
Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.
2010–2024
P0408 on the A4 3.0 TDI V6 (CCWA, CTBA, CAPA codes) means the bank-2 EGR position sensor has failed open. Bank 2 is the passenger side on RHD markets, driver side on LHD markets. The bank-2 EGR is behind the engine and significantly harder to reach than bank 1, which is why labor for sensor B repairs is higher. Many workshops replace both valves together to avoid a repeat repair.
Costi stimati per i proprietari di Audi A4adeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Audi
Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.
2014–2024
OM642 V6 Sprinters (3.0 CDI) develop P0408 when the bank-2 EGR position sensor fails open. The bank-2 EGR sits in a heat-stressed location near the firewall, and connector seal failure leading to open circuits is common past 120,000 km. XENTRY adaptation reset for both EGR banks is mandatory after service. OM651 4-cylinder Sprinters do not normally have a sensor B.
Costi stimati per i proprietari di Mercedes Sprinteradeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Mercedes-Benz
Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.
Questi codici compaiono spesso insieme a P0408 o indicano problemi correlati:
P0407 means sensor B signal is too low (short to ground or failed sensor). P0408 means sensor B signal is too high (open wire, missing ground, or sensor failed open). The diagnostic approach is similar, but the failure modes are opposite.
Short distances yes. The ECU disables EGR on the affected bank, so the engine runs without that EGR. Diesels may enter limp mode. Long-term driving accelerates intake carbon buildup and may trigger secondary DPF or SCR faults. Plan repair within a few weeks.
Because most 4-cylinder engines only have a single EGR position sensor. Sensor B exists on engines with dual EGR valves (Audi 3.0 TDI V6, Mercedes OM642 V6, BMW B57 with high/low pressure EGR) or on engines with redundant feedback sensors. On a 4-cylinder, P0408 is unusual and usually means a calibration or labeling quirk.
Not always, but it is recommended on high-mileage cars (over 150,000 km) because both valves share the same age, soot exposure, and thermal cycling. If one EGR valve has failed, the other is usually close behind. Workshops often quote both for cost efficiency, since labor for the second side is much lower once the engine is partially apart.
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