P0406: Exhaust Gas Recirculation Sensor "A" Circuit High
Moderate SeveritySafe to drive (short-term)Emissions
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.
Estimated repair costFrom €70 to €670+, varies by vehicle
What does P0406 mean?
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.
P0406 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0406 and illuminates the check engine light.
What are the symptoms of P0406?
If your vehicle has triggered P0406, you may notice one or more of these symptoms:
Check engine light illuminated
Rough idle, sometimes stalling at stops
Reduced power on diesels (limp mode)
Hesitation during light throttle
Failed emissions test or periodic technical inspection
What causes P0406?
Here are the most common causes of P0406, ranked by how likely they are to be the culprit:
highEGR position sensor failed open internally (sensor shorted to 5V reference)
highOpen or broken signal wire between sensor and ECU
mediumLoose or unseated EGR sensor connector
mediumCarbon buildup holding valve at maximum reported position
lowOpen ground circuit on the sensor side
Is it safe to drive with P0406?
Generally yes, for short-term driving. Driveable. P0406 means the EGR position sensor (sensor A) is reporting a voltage higher than the expected range. The ECU loses trust in the EGR feedback and disables the system, causing rough idle and possible limp mode on diesels. Failed emissions test is guaranteed.
How do you diagnose P0406?
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?
Repair costs for P0406 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 EGR sensor connector
€10–€60
€60–€180
€70–€240
Moderate
Replace EGR valve (sensor integrated)
€150–€450
€80–€220
€230–€670
Moderate
Repair EGR wiring harness or signal wire
€20–€120
€120–€350
€140–€470
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0406 on specific vehicles
P0406 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0406 on BMW 3 Series
BMW 3 Series • 2007–2024
The N47 and B47 320d EGR sensor fails high (P0406) less often than low (P0405), but when it does it usually means the integrated sensor has failed internally rather than a wiring issue. The EGR connector is buried under the intake manifold support, requiring partial disassembly for inspection. ISTA or Carly adaptation reset is mandatory after valve replacement on the B47.
What causes P0406 on a BMW 3 Series?
BMW 3 SeriesN47/B47 integrated sensor internal failure (open Hall element)
BMW 3 SeriesConnector buried under intake support, hard to inspect
P0406 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 EGR sensor connector
€14–€84
€84–€252
€98–€336
Moderate
Replace EGR valve (sensor integrated)
€210–€630
€112–€308
€322–€938
Moderate
Repair EGR wiring harness or signal wire
€28–€168
€168–€490
€196–€658
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0406 on Volkswagen Golf
Volkswagen Golf • 2009–2024
EA189 and EA288 TDI Golfs occasionally throw P0406 after harness work or accessory installation that disturbs the EGR connector. Always check that the connector is fully clicked in before replacing parts. On EA288 (2014+), the connector lock tab can crack from age, allowing the connector to back out under engine vibration. VCDS measured value block confirms the sensor voltage.
What causes P0406 on a Volkswagen Golf?
Volkswagen GolfEA189/EA288 connector lock tab cracking, allowing back-out under vibration
Volkswagen GolfDisturbed connectors after intake or turbo service
P0406 repair cost for Volkswagen Golf
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 EGR sensor connector
€12–€69
€69–€207
€81–€276
Moderate
Replace EGR valve (sensor integrated)
€173–€518
€92–€253
€265–€770
Moderate
Repair EGR wiring harness or signal wire
€23–€138
€138–€402
€161–€541
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0406 on Audi A4
Audi A4 • 2008–2024
B8 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 A4?
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
P0406 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 EGR sensor connector
€13–€75
€75–€225
€88–€300
Moderate
Replace EGR valve (sensor integrated)
€188–€563
€100–€275
€288–€838
Moderate
Repair EGR wiring harness or signal wire
€25–€150
€150–€438
€175–€588
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0406 on Mercedes Sprinter
Mercedes Sprinter • 2010–2024
OM651 Sprinter EGR sensor open-circuit failures are less common than shorts (P0405), but when they appear they often correlate with a recent winter where road salt damaged the connector pins. Repair attempts at the harness rarely last, so most workshops fit a new pigtail connector with heat-shrink seals and a fresh EGR valve. XENTRY adaptation reset is mandatory.
What causes P0406 on a Mercedes Sprinter?
Mercedes SprinterOM651 connector pin damage from winter road salt causing open circuit
Mercedes SprinterHeat-shrink pigtail repair plus new valve typical fix
P0406 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 EGR sensor connector
€13–€78
€78–€234
€91–€312
Moderate
Replace EGR valve (sensor integrated)
€195–€585
€104–€286
€299–€871
Moderate
Repair EGR wiring harness or signal wire
€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 P0406 or indicate related issues:
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.
Scan your car with Skanyx to diagnose P0406
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