P0674 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
P0674 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 4. Glow plugs preheat each combustion chamber so a cold diesel can ignite. The code identifies the cylinder 4 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.
- Severity
- Moderate · Electrical
- Typical repair cost, all makes
- €5-€420
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Mercedes-Benz and Skanyx tells you what P0674 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0674 mean on a Mercedes-Benz?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0674.
Mercedes-Benz (OM651 diesel)
2008-2018
The OM651 control module monitors each plug and reports per-cylinder faults, so P0674 points at cylinder 4. 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 P0674 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0674 page, these are the patterns noted for Mercedes-Benz models:
Failed cylinder 4 plug on OM651
: Mercedes-Benz (OM651 diesel)
Seized plug on neglected high-mileage engines
: Mercedes-Benz (OM651 diesel)
How to diagnose P0674 on a Mercedes-Benz with OBD2
- Read the stored code and freeze frame with Skanyx or any ELM327 adapter to confirm P0674 and note the start temperature when it set
- Locate the cylinder 4 glow plug and inspect its connector and wiring for corrosion, looseness, or damage
- Disconnect the cylinder 4 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 4 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 4 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 P0674 cost to fix on a Mercedes-Benz? (EUR)
Estimated repair costs for P0674 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace cylinder 4 glow plug (DIY) | €10–€30 | €0–€0 | €10–€30 | Moderate |
| Repair cylinder 4 connector/wiring (DIY) | €5–€25 | €0–€0 | €5–€25 | Moderate |
| Replace cylinder 4 glow plug (shop) | €10–€30 | €40–€120 | €50–€150 | Moderate |
| Replace full glow plug set as preventive (shop) | €60–€200 | €90–€220 | €150–€420 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0674
These codes are often seen alongside P0674 or point to related issues, on any make:
Looking for the full P0674 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0674 guide