The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0406.
DTC/P0406·Mercedes-Benz
P0406 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Mercedes-Benz
P0406 on a Mercedes-Benz means 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 or ground wire, a short to the 5V reference, or a sensor that has failed internally and drives its signal high.
Typical repair cost, all makes€70 - €670
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Mercedes Sprinter
2010-2024On OM651 Sprinters an open circuit in the EGR sensor wiring is often traced to road salt reaching the connector pins. A patched harness rarely lasts once salt has reached the pins, so fit a new pigtail connector with heat-shrink seals rather than repairing the old one. An EGR adaptation with manufacturer-level software (XENTRY) is normally part of the job after valve replacement.
What causes P0406 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0406 page, these are the patterns noted for Mercedes-Benz models:
Mercedes SprinterOM651 connector pin damage from winter road salt causing open circuit
Mercedes SprinterHeat-shrink pigtail repair plus new valve typical fix
How to diagnose P0406 on a Mercedes-Benz with OBD2
Follow these steps to pinpoint the root cause of P0406:
- Back-probe the sensor signal wire at the sensor with the key on, engine off. A reading near 5V there with the valve closed points to the sensor or a short to the reference; a normal reading at the sensor but a high value in live data points to a break in the signal wire towards the ECU
- 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
- Check the signal wire for continuity between the sensor connector and the ECU, and for a short to the 5V reference or battery voltage. Use the wiring diagram to see how the ECU treats an unplugged input, because whether it floats high or low depends on the ECU design
- 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 Mercedes-Benz? (EUR)
Estimated repair costs for P0406 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to P0406
These codes are often seen alongside P0406 or point to related issues, on any make:
Looking for the full P0406 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0406 guideSkanyx · Mercedes-Benz
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