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.
DTC/P0408·Audi
P0408 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0408 on a Audi 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.
Repair cost on Audi€88 - €913
What does P0408 mean on a Audi?
Audi A4
2010–2024P0408 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?
Beyond the generic causes listed on the main P0408 page, these are the Audi-specific patterns we see most often:
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
How to diagnose P0408 on a Audi with OBD2
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 on a Audi? (EUR)
Estimated repair costs on a Audi (Audi parts and labour typically run 25% above the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0408 on Audi
These codes commonly cluster with P0408 on Audi vehicles:
FAQ: P0408 on Audi
What is the difference between P0407 and P0408?
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.
Looking for the full P0408 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0408 guideSkanyx · Audi
Diagnosing P0408 on your Audi?
Connect any Bluetooth OBD2 adapter, scan for codes, and get AI-powered diagnostics with severity ratings and repair cost estimates.
Download Skanyx