The Quick Answer above is the generic definition. What follows is what is documented for the Mercedes-Benz models that log P0671, checked against manufacturer data and owner reports.
DTC/P0671·Mercedes-Benz
P0671 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Mercedes-Benz
P0671 on a Mercedes-Benz is a diesel-only code meaning the engine control unit detected an electrical fault in the glow plug circuit for cylinder 1. Glow plugs preheat each combustion chamber so a cold diesel can ignite. The code identifies the cylinder 1 circuit specifically, usually pointing to a failed plug, its wiring, or its connection rather than the whole system. Repairs typically run 30-180 EUR for a single plug and circuit fix.
Repair cost on Mercedes-Benz€5 - €420
Connect any standard Bluetooth OBD2 adapter to your Mercedes-Benz and Skanyx tells you what P0671 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
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Mercedes-Benz (OM651 diesel)
2008-2018The OM651 control module monitors each plug and reports per-cylinder faults, so P0671 points at cylinder 1. Mercedes per-plug data beyond the generic code is manufacturer-extended and needs XENTRY. Plug access is moderate, but seized plugs on neglected engines can complicate what is otherwise a simple single-plug replacement.
What causes P0671 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0671 page, these are the documented Mercedes-Benz-specific patterns:
Mercedes-Benz (OM651 diesel)Failed cylinder 1 plug on OM651
Mercedes-Benz (OM651 diesel)Seized plug on neglected high-mileage engines
How to diagnose P0671 on a Mercedes-Benz with OBD2
Follow these steps to pinpoint the root cause of P0671:
- Read the stored code and freeze frame with Skanyx or any ELM327 adapter to confirm P0671 and note the start temperature when it set
- Locate the cylinder 1 glow plug and inspect its connector and wiring for corrosion, looseness, or damage
- Disconnect the cylinder 1 glow plug and bench-test it with a multimeter: a healthy plug reads roughly 0.5-2 ohm, while an open (infinite) reading confirms that plug has failed
- If the cylinder 1 plug is good, check continuity of its wiring back to the control module and verify a clean ground
- Remember that per-cylinder glow plug live status is manufacturer-extended (Mode $22) data, not generic OBD2, so the multimeter test on the cylinder 1 plug is how you confirm the failure
- Consider replacing the full set if the plugs are original and high-mileage, since the others are likely to fail soon
How much does P0671 cost to fix on a Mercedes-Benz? (EUR)
Estimated repair costs for P0671 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.
Related codes that often appear with P0671 on Mercedes-Benz
These codes commonly cluster with P0671 on Mercedes-Benz vehicles:
Looking for the full P0671 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0671 guideSkanyx · Mercedes-Benz
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