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DTC/P0307·Mercedes-Benz

P0307 on Mercedes-Benz: Causes, Symptoms and Fix Cost

Quick Answer
High SeverityNot safe to driveMercedes-Benz

P0307 on a Mercedes-Benz means the engine computer has counted repeated misfires on cylinder 7. The code can only appear on engines with at least seven cylinders, which in practice means V8s, V10s and V12s. The usual culprits are the cylinder 7 spark plug or ignition coil, followed by the injector, an intake leak and, less often, a mechanical fault in that cylinder.

Typical repair cost, all makes€55 - €2700

Connect any standard Bluetooth OBD2 adapter to your Mercedes-Benz and Skanyx tells you what P0307 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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What does P0307 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 P0307.

Mercedes-Benz S500 / S550 (W221, M273 V8)

2005-2011

The M273 V8 is port-injected, so the intake-valve carbon that troubles direct-injection V8s is not the usual suspect; start with the coil, plug and injector. The M273 can also wear the sprocket on its timing-chain idler gear, which sets camshaft correlation codes (P0016 to P0019) and rough running. If one of those is stored alongside the misfire, deal with the timing first.

What causes P0307 on a Mercedes-Benz?

Beyond the generic causes listed on the main P0307 page, these are the patterns noted for Mercedes-Benz models:

Mercedes-Benz S500 / S550 (W221, M273 V8)Worn spark plug or failing coil on cylinder 7
Mercedes-Benz S500 / S550 (W221, M273 V8)Worn timing-chain idler sprocket upsetting camshaft timing

How to diagnose P0307 on a Mercedes-Benz with OBD2

Follow these steps to pinpoint the root cause of P0307:

  1. Read all stored and pending codes plus the freeze frame. Note whether other cylinders also log misfires and whether lean codes (P0171, P0174) or camshaft correlation codes (P0016 to P0019) are stored, because those point to a shared cause rather than one cylinder.
  2. Find cylinder 7 in the service data for your engine before removing anything. V8 numbering differs by maker: GM puts the odd-numbered cylinders on the left bank, while Ford numbers one bank 1 to 4 and the other 5 to 8.
  3. Pull the cylinder 7 coil and plug. Oil on the plug points to valve stem seals or rings, black soot to a rich mixture, and a cracked or blistered insulator to a plug that has overheated.
  4. Swap the cylinder 7 coil with one from a neighbouring cylinder, clear the codes and drive. If the misfire moves with the coil, replace the coil.
  5. If the misfire stays on cylinder 7, check the injector. On port-injected engines you can listen for its click with a stethoscope; direct injectors run at very high pressure and are best tested by a workshop.
  6. Watch live fuel trims for the bank containing cylinder 7. A lean trim on that bank alone points to an intake leak or a weak injector on that side; a smoke test finds the leak.
  7. If ignition and fuel check out, run a compression and leak-down test on cylinder 7. A reading clearly below the other cylinders means valve, ring or lifter trouble.
  8. After the repair, clear the codes and drive a mix of idle, steady cruising and acceleration, then check that no misfire code returns.

How much does P0307 cost to fix on a Mercedes-Benz? (EUR)

Estimated repair costs for P0307 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 spark plug on cylinder 7 (on a V8 usually the full set of eight) €15–€120 €40–€200 €55–€320 Moderate
Replace ignition coil on cylinder 7 €40–€180 €30–€150 €70–€330 Easy
Clean or replace fuel injector on cylinder 7 €60–€250 €80–€150 €140–€400 Professional
Intake manifold gasket or vacuum hose repair €40–€150 €150–€400 €190–€550 Moderate
Cylinder head, valve or lifter work after a failed compression or leak-down test €300–€1200 €400–€1500 €700–€2700 Professional

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

These codes are often seen alongside P0307 or point to related issues, on any make:

P0300P0305P0306Mercedes-BenzP0308Mercedes-BenzP0357P0171P0174Mercedes-BenzP0420

Looking for the full P0307 reference (all makes, full diagnosis flow, complete repair cost matrix)?

See the main P0307 guide
Skanyx · Mercedes-Benz

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Your car logged P0307. Skanyx reads it on any standard Bluetooth OBD2 adapter, tells you whether it is safe to keep driving, and shows the €55-€2700 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.

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