P0405: Exhaust Gas Recirculation Sensor "A" Circuit Low
Moderate SeveritySafe to drive (short-term)Emissions
P0405 means the EGR position sensor 'A' (the primary feedback sensor on the EGR valve) is sending a voltage below the normal operating range, typically below 0.2V. This is almost always a wiring fault, a corroded connector, or a sensor that has failed shorted to ground.
Estimated repair costFrom €70 to €670+, varies by vehicle
What does P0405 mean?
P0405 means the EGR position sensor 'A' (the primary feedback sensor on the EGR valve) is sending a voltage below the normal operating range, typically below 0.2V. This is almost always a wiring fault, a corroded connector, or a sensor that has failed shorted to ground.
P0405 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0405 and illuminates the check engine light.
What are the symptoms of P0405?
If your vehicle has triggered P0405, you may notice one or more of these symptoms:
Check engine light illuminated
Rough or hunting idle
Reduced power, especially on diesels in limp mode
Hesitation during acceleration
Failed emissions or periodic technical inspection
What causes P0405?
Here are the most common causes of P0405, ranked by how likely they are to be the culprit:
highEGR position sensor shorted to ground internally
highDamaged signal wire between sensor and ECU (chafed, grounded)
mediumCorroded or water-damaged sensor connector pulling signal low
mediumOpen 5V reference supply to the sensor
lowFailed ECU 5V reference circuit (rare, usually affects multiple sensors)
Is it safe to drive with P0405?
Generally yes, for short-term driving. Driveable. P0405 means the EGR position sensor (sensor A) is reporting a voltage lower than the expected operating range. The ECU loses confidence in EGR position feedback and may disable the EGR system or enter limp mode. Expect rough idle and a failed emissions test.
How do you diagnose P0405?
Follow these steps to pinpoint the root cause of P0405:
Back-probe the sensor signal wire with the key on, engine off. A healthy sensor at rest should read 0.5–1.0V (varies by vehicle, check workshop spec)
Verify 5V reference at the sensor connector. If reference is missing, trace the wire back toward the ECU
Unplug the sensor connector and inspect for water intrusion, corrosion, and bent pins
With the connector unplugged, the signal wire should read 5V at the ECU side. If it reads 0V, the wire is shorted to ground
If wiring and reference are good, the sensor itself is the most likely failure. On most modern systems, replacing the integrated valve assembly is the practical fix
How much does P0405 cost to fix?
Repair costs for P0405 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean and repair EGR sensor connector
€10–€60
€60–€180
€70–€240
Moderate
Replace EGR valve (sensor integrated)
€150–€450
€80–€220
€230–€670
Moderate
Repair or replace EGR wiring harness section
€20–€120
€120–€350
€140–€470
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0405 on specific vehicles
P0405 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0405 on BMW 3 Series
BMW 3 Series • 2007–2024
The N47 and B47 320d EGR position sensor sits in a heat-soaked location near the turbo, and is integrated into the EGR valve. P0405 typically appears around 120,000 km, often after the connector seal degrades and lets moisture in. INPA or ISTA can confirm the sensor voltage in the live data screen. Always reset adaptation values after valve replacement.
What causes P0405 on a BMW 3 Series?
BMW 3 SeriesN47/B47 integrated position sensor degradation from heat soak
BMW 3 SeriesConnector seal failure allowing moisture into Hall sensor
P0405 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
Clean and repair EGR sensor connector
€14–€84
€84–€252
€98–€336
Moderate
Replace EGR valve (sensor integrated)
€210–€630
€112–€308
€322–€938
Moderate
Repair or replace EGR wiring harness section
€28–€168
€168–€490
€196–€658
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0405 on Volkswagen Golf
Volkswagen Golf • 2009–2024
On EA189 and EA288 TDI Golfs, P0405 is often caused by harness chafing where the EGR loom passes near the EGR cooler. The chafed signal wire grounds against the cooler body and pulls the sensor voltage low. VCDS group 99 (EA189) or group 144 (EA288) shows the live sensor voltage. Repair the chafe with high-temp tape and replace the affected sensor wire section.
What causes P0405 on a Volkswagen Golf?
Volkswagen GolfEA189/EA288 harness chafing against EGR cooler shorting signal to ground
Volkswagen GolfConnector pin corrosion on early EA189 cars (2009–2012)
P0405 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
Clean and repair EGR sensor connector
€12–€69
€69–€207
€81–€276
Moderate
Replace EGR valve (sensor integrated)
€173–€518
€92–€253
€265–€770
Moderate
Repair or replace EGR wiring harness section
€23–€138
€138–€402
€161–€541
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0405 on Audi A4
Audi A4 • 2008–2024
B8 and B9 A4 2.0 TDI models share the EGR sensor failure modes with the Golf. The B8 has tighter packaging that makes the connector harder to access without removing the intake duct. On 3.0 TDI V6 (CCWA, CTBA), P0405 may indicate which bank with a suffix in the freeze frame data, but verify in VCDS first. Adaptation reset via VCDS or ODIS is required after valve replacement.
What causes P0405 on a Audi A4?
Audi A4EA189/EA288 sensor failure with restricted B8/B9 access
Audi A43.0 TDI V6 bank-specific fault requires freeze-frame review
P0405 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
Clean and repair EGR sensor connector
€13–€75
€75–€225
€88–€300
Moderate
Replace EGR valve (sensor integrated)
€188–€563
€100–€275
€288–€838
Moderate
Repair or replace EGR wiring harness section
€25–€150
€150–€438
€175–€588
Professional
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0405 on Mercedes Sprinter
Mercedes Sprinter • 2010–2024
OM651 Sprinter EGR position sensors fail regularly under heavy commercial use, often before 120,000 km. The Mercedes connector is exposed and prone to road salt corrosion in northern European winters. P0405 frequently appears alongside P0401 or P0404, and Star Diagnosis (XENTRY) is needed for proper adaptation reset after replacement. Aftermarket EGR valves with integrated sensors are available, but quality varies.
What causes P0405 on a Mercedes Sprinter?
Mercedes SprinterOM651 Hall-effect sensor failure from heavy commercial duty cycles
Mercedes SprinterRoad salt corrosion at exposed connector in winter operation
P0405 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
Clean and repair EGR sensor connector
€13–€78
€78–€234
€91–€312
Moderate
Replace EGR valve (sensor integrated)
€195–€585
€104–€286
€299–€871
Moderate
Repair or replace EGR wiring harness section
€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 P0405 or indicate related issues:
Short distances yes. The ECU disables EGR control when the position sensor signal is unreliable, so the engine runs without EGR (more NOx, more pinging on petrol, possible limp mode on diesel). Resolve within a couple of weeks to avoid intake carbon buildup and emissions test failure.
Is P0405 the sensor or the wiring?
About 60% of the time it is the integrated sensor failing inside the EGR valve. The other 40% is wiring or connector corrosion. Always inspect the connector and measure the 5V reference at the sensor before condemning the valve, since wiring repairs are far cheaper.
Can I just replace the EGR sensor without the valve?
On older vehicles with separate DPFE sensors (older Fords, some Japanese makes), yes. On modern BMW, Mercedes, and VAG vehicles the sensor is integrated into the EGR valve and not available separately. You replace the whole valve assembly.
Why is the EGR position sensor failing on my diesel?
Diesel EGR valves run hot and dirty. The position sensor sits directly on the valve, so it sees constant thermal cycling and soot. Hall-effect sensors degrade over time, and the connector seals fail. Failure between 100,000–150,000 km is typical on BMW N47/B47 and VW EA189/EA288.
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