P0408: Exhaust Gas Recirculation Sensor "B" Circuit High
Moderate SeveritySafe to drive (short-term)Emissions
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.
Estimated repair costFrom €70 to €730+, varies by vehicle
What does P0408 mean?
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 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0408 and illuminates the check engine light.
What are the symptoms of P0408?
If your vehicle has triggered P0408, you may notice one or more of these symptoms:
Check engine light illuminated
Rough idle, uneven cylinder firing on V6/V8 diesels
Reduced power and possible limp mode on diesels
Hesitation during light throttle
Failed emissions or periodic technical inspection
What causes P0408?
Here are the most common causes of P0408, ranked by how likely they are to be the culprit:
highSensor B failed open internally (open circuit inside sensor element)
highOpen signal wire or broken connector pin on sensor B
mediumMissing sensor B ground connection
mediumLoose or unseated sensor B connector after recent service
lowFailed ECU 5V reference circuit (rare, usually affects multiple sensors)
Is it safe to drive with P0408?
Generally yes, for short-term driving. 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.
How do you diagnose P0408?
Follow these steps to pinpoint the root cause of P0408:
Identify sensor B in the workshop manual. On V6/V8 diesels this is normally the bank opposite to sensor A
Back-probe sensor B signal wire. Reading near 5V with key on indicates an open signal or sensor failed open
Verify sensor B ground at the connector. Missing ground will let the signal float high
Inspect for loose connector locks, especially after recent intake or turbo service
If signal stays high with the connector fully seated and ground confirmed, replace the integrated valve or sensor assembly. Reset adaptation values with a manufacturer-spec scan tool
How much does P0408 cost to fix?
Repair costs for P0408 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Re-seat and clean sensor B connector
€10–€60
€60–€180
€70–€240
Moderate
Replace EGR valve B (sensor integrated)
€150–€450
€100–€280
€250–€730
Moderate
Repair EGR sensor B wiring harness branch
€20–€120
€120–€350
€140–€470
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0408 on specific vehicles
P0408 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0408 on BMW 3 Series
BMW 3 Series • 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.
What causes P0408 on a BMW 3 Series?
BMW 3 SeriesB57 low-pressure EGR sensor open failure from heat-stressed harness routing
BMW 3 SeriesConnector failure behind DPF area at 130,000+ km
P0408 repair cost for BMW 3 Series
Estimated costs for BMW 3 Series ownersadjusted higher than average due to BMW-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Re-seat and clean sensor B connector
€14–€84
€84–€252
€98–€336
Moderate
Replace EGR valve B (sensor integrated)
€210–€630
€140–€392
€350–€1022
Moderate
Repair EGR sensor B wiring harness branch
€28–€168
€168–€490
€196–€658
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0408 on Volkswagen Golf
Volkswagen Golf • 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.
What causes P0408 on a Volkswagen Golf?
Volkswagen GolfMarket-specific calibration label issue on standard EA189/EA288
Estimated costs for Volkswagen Golf ownersadjusted higher than average due to Volkswagen-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Re-seat and clean sensor B connector
€12–€69
€69–€207
€81–€276
Moderate
Replace EGR valve B (sensor integrated)
€173–€518
€115–€322
€288–€839
Moderate
Repair EGR sensor B wiring harness branch
€23–€138
€138–€402
€161–€541
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0408 on Audi A4
Audi A4 • 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.
What causes P0408 on a Audi A4?
Audi A43.0 TDI V6 bank-2 EGR sensor open failure, harder access than bank 1
Audi A4Both valves typically replaced together on high-mileage cars
P0408 repair cost for Audi A4
Estimated costs for Audi A4 ownersadjusted higher than average due to Audi-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Re-seat and clean sensor B connector
€13–€75
€75–€225
€88–€300
Moderate
Replace EGR valve B (sensor integrated)
€188–€563
€125–€350
€313–€913
Moderate
Repair EGR sensor B wiring harness branch
€25–€150
€150–€438
€175–€588
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0408 on Mercedes Sprinter
Mercedes Sprinter • 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.
What causes P0408 on a Mercedes Sprinter?
Mercedes SprinterOM642 V6 bank-2 EGR sensor open failure from heat-stressed firewall location
Mercedes SprinterConnector seal failure past 120,000 km causing open circuit
P0408 repair cost for Mercedes Sprinter
Estimated costs for Mercedes Sprinter ownersadjusted higher than average due to Mercedes-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Re-seat and clean sensor B connector
€13–€78
€78–€234
€91–€312
Moderate
Replace EGR valve B (sensor integrated)
€195–€585
€130–€364
€325–€949
Moderate
Repair EGR sensor B wiring harness branch
€26–€156
€156–€455
€182–€611
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
These codes are often seen alongside P0408 or indicate related issues:
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.
Can I drive with P0408?
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.
Why does P0408 only appear on V6 or V8 engines?
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.
Do I have to replace both EGR valves on a V6 diesel?
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.
Scan your car with Skanyx to diagnose P0408
Connect any Bluetooth OBD2 adapter, scan for codes, and get AI-powered diagnostics with severity ratings and repair cost estimates.
