P0406 means the EGR position sensor 'A' is sending a voltage above its normal operating range, typically above 4.5V. This is usually caused by an open signal wire, a sensor shorted to its 5V reference internally, or a sensor that has failed in the open position.
DTC/P0406·Audi
P0406 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0406 on a Audi means the EGR position sensor 'A' is sending a voltage above its normal operating range, typically above 4.5V. This is usually caused by an open signal wire, a sensor shorted to its 5V reference internally, or a sensor that has failed in the open position.
Repair cost on Audi€88 - €838
What does P0406 mean on a Audi?
Audi A4
2008–2024B8 and B9 A4 2.0 TDI suffer the same P0406 failure modes as the Golf, plus restricted access due to the larger intake manifold. On 3.0 TDI V6 models, P0406 may apply to either bank, so always read the freeze frame to confirm which side. Adaptation reset via VCDS or ODIS is required after sensor or valve service.
What causes P0406 on a Audi?
Beyond the generic causes listed on the main P0406 page, these are the Audi-specific patterns we see most often:
Audi A4EA189/EA288 connector issues identical to Golf, with restricted A4 access
Audi A43.0 TDI V6 dual-bank fault requires freeze-frame to identify side
How to diagnose P0406 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0406:
- Back-probe the sensor signal wire with the key on, engine off. Reading near 5V indicates an open signal or sensor failed open
- Verify the sensor ground at the connector. If ground is missing, the signal will float high
- Unplug the connector and check for damaged pins or unseated terminals
- With the connector unplugged, the signal wire at the sensor side should read 0V (the sensor pulls it up when connected). At the ECU side it should still read 5V
- If wiring and ground are good and the sensor reads 5V steadily, the integrated sensor has failed. Replace the EGR valve assembly
How much does P0406 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 P0406 on Audi
These codes commonly cluster with P0406 on Audi vehicles:
FAQ: P0406 on Audi
What is the difference between P0405 and P0406?
P0405 means the signal is too low (below ~0.2V), usually a short to ground or failed sensor. P0406 means the signal is too high (above ~4.5V), usually an open wire, missing ground, or sensor failed open. Diagnostic steps are similar but the failure modes are opposite.
Can I drive with P0406?
Yes, short distances. The ECU disables EGR control, so the engine runs without EGR. Expect rough idle and possible limp mode on diesels. Long-term driving accelerates intake carbon buildup, especially on direct-injection engines. Plan the repair within a few weeks.
Is EGR delete a legal workaround for P0406?
No. EGR delete is illegal across the EU and UK, raises NOx emissions above legal limits, and fails periodic technical inspection (TÜV, ITV, TA, SKP). It can also void insurance and prevent vehicle registration transfer. Always repair the sensor or valve properly.
Why does P0406 come back after I replaced the sensor?
Two common reasons. First, EGR adaptation values were not reset after the new valve was fitted (required on BMW, Mercedes, VAG). Second, the carbon buildup that caused the original sensor stress is still present and damages the new sensor within months. Always clean the intake passages alongside any valve replacement.
Looking for the full P0406 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0406 guideSkanyx · Audi
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