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 est un code defaut lie a emissions, classe en gravite moderate. Lorsque le calculateur de ton vehicule detecte cette condition, il enregistre P0408 et allume le voyant moteur.
Si ton vehicule a declenche P0408, tu peux remarquer un ou plusieurs de ces symptomes :
Voici les causes les plus courantes de P0408, classees selon la probabilite qu'elles soient en cause :
En general oui, pour des trajets courts. 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.
Suis ces etapes pour identifier la cause profonde de P0408 :
Les couts de reparation de P0408 varient selon la cause profonde et ton vehicule. Voici des estimations courantes :
Prix estimes au March 2026. Les couts varient selon la region, le vehicule et le garage.
P0408 se comporte differemment selon ton vehicule. Selectionne ta voiture ci-dessous pour des causes propres au modele, les problemes connus et des estimations de couts ajustees :
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.
Couts estimes pour les proprietaires de BMW 3 Seriesajuste a la hausse par rapport a la moyenne en raison du prix des pieces specifiques a BMW
Prix estimes au March 2026. Les couts varient selon la region, le vehicule et le garage.
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.
Couts estimes pour les proprietaires de Volkswagen Golfajuste a la hausse par rapport a la moyenne en raison du prix des pieces specifiques a Volkswagen
Prix estimes au March 2026. Les couts varient selon la region, le vehicule et le garage.
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.
Couts estimes pour les proprietaires de Audi A4ajuste a la hausse par rapport a la moyenne en raison du prix des pieces specifiques a Audi
Prix estimes au March 2026. Les couts varient selon la region, le vehicule et le garage.
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.
Couts estimes pour les proprietaires de Mercedes Sprinterajuste a la hausse par rapport a la moyenne en raison du prix des pieces specifiques a Mercedes-Benz
Prix estimes au March 2026. Les couts varient selon la region, le vehicule et le garage.
Ces codes apparaissent souvent avec P0408 ou indiquent des problemes connexes :
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.
Branche un adaptateur OBD2 Bluetooth standard, scanne les codes et obtiens un diagnostic par IA avec niveaux de gravite et estimations des couts de reparation.
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