Every Mercedes engine has its weak points. This index lists the most common failures, organised by engine code, model, and symptom type. All data is backed by 9,000+ UK enquiries and verified by our specialist network.
Mercedes engine failures are often predictable and well-documented. The most common issues include timing chain stretch (OM651, M276), injector seal leaks (OM651, OM642), oil cooler seal leaks (OM642), and balance shaft wear (M272). In 2025, the OM651 was the most enquired‑about engine, with 1,250 requests [EM‑VERIFIED].
For a full overview of Mercedes engines and fitment, see the fitment matrix.
Click any engine code to see the most common failures, symptoms, and repair costs for that specific engine.
2.1‑litre four‑cylinder diesel. Common failures: timing chain tensioner wear, injector seal leaks (Black Death), DPF/EGR clogging.
OM651 Balance Shaft Failure OM651 Injector Seal Failure3.0‑litre V6 diesel. Common failures: oil cooler seal leak, swirl flap motor failure, turbo seal leaks.
OM642 Swirl Flap Failure OM642 Oil Cooler Seal Leak3.0‑litre V6 petrol. Common failures: timing chain stretch, carbon buildup on intake valves, oil leaks from gaskets.
M276 Camshaft Adjuster Failure M276 Timing Chain Stretch3.5‑litre V6 petrol. Common failures: balance shaft timing chain wear, intake manifold swirl flap issues.
M272 Balance Shaft Chain Failure2.0‑litre four‑cylinder diesel. Common failures: AdBlue system issues, EGR cooler failures, occasional timing chain wear.
OM654 Injector Seal Failure5.5‑litre V8 biturbo. Common failures: timing chain adjuster wear, oil leaks from valve covers.
M157 Timing Chain Adjuster FailureFor a complete list of all engine codes and their failure profiles, see the Engine Knowledge Centres.
Common engine failures grouped by the Mercedes model they affect most frequently.
W204, W205, W206. Most common failures: OM651 timing chain (W204/W205), OM654 AdBlue issues (W205/W206), M272 balance shaft (W204).
C‑Class OM651 Failure C‑Class M272 FailureW211, W212, W213. Most common failures: OM642 oil cooler seal (W211/W212), OM651 timing chain (W212), M276 timing chain (W213).
E‑Class OM642 Failure E‑Class M276 FailureW166, V167. Most common failures: OM642 oil cooler seal, M276 timing chain, OM654 AdBlue.
GLE OM642 Oil Cooler LeakW221, W222. Most common failures: OM642 oil cooler seal, M276 timing chain, M157 adjuster wear.
S‑Class M157 FailureW906, W907. Most common failures: OM651 injector seal leaks, DPF clogging, OM642 swirl flap.
Sprinter OM651 Injector SealFor a complete model‑specific guide, see the fitment matrix.
Diagnose your issue by the symptom you're experiencing. Each symptom links to the most likely failure pages.
For a full list of symptoms and their possible causes, visit the Symptom Hub.
Based on our proprietary data from 24,650 quote requests and interviews with specialists, these are the most frequently reported failures across all Mercedes models.
| Failure Type | Affected Engines | Typical Mileage | Typical Repair Cost | Severity |
|---|---|---|---|---|
| Timing chain tensioner wear | OM651 | 80k–150k | £600–£1,500 [EM‑QUOTE] | Catastrophic |
| Injector seal leakage (Black Death) | OM651 | 80k–150k | £400–£1,200 | Immediate |
| Swirl flap motor failure | OM642 | 70k–150k | £500–£1,200 | Immediate |
| Oil cooler seal leak | OM642 | 70k–150k | £800–£1,500 | Monitor |
| Camshaft adjuster wear | M276 | 60k–120k | £1,500–£2,500 | Catastrophic |
| Balance shaft chain wear | M272 | 60k–120k | £1,500–£3,000 | Catastrophic |
| Timing chain adjuster wear | M157 | 70k–120k | £1,500–£3,000 | Catastrophic |
| AdBlue/EGR issues | OM654 | 100k–180k | £500–£1,500 | Monitor |
For a complete list of all documented failure patterns, see the Engine Failure Index 2026.
Based on our 2025 enquiry data, the OM651 timing chain tensioner wear is the most frequently reported failure, with 1,250 requests. It affects C‑Class, E‑Class, GLC, and Sprinter models. Early detection is critical.
Listen for cold‑start rattle, look for blue or black smoke, check for oil in coolant, and watch for warning lights. Use our Symptom Hub to narrow down the issue.
It depends on the vehicle value and the repair cost. Use the 70% scrap threshold as a guideline: if the repair cost exceeds 70% of the car's value, consider scrapping. See the repair/replace/scrap framework for worked examples.
Costs vary widely. A reconditioned OM651 supply‑only is around £2,800–£4,800, while an OM642 is £3,200–£5,500, and an M276 is £3,800–£6,500 [EM‑QUOTE]. See the replacement cost guide for a full breakdown.
Regular maintenance is key. Use the correct oil, change it on time, and follow the manufacturer's service schedule. For specific engines, see the preventative advice on each failure page.
Understanding the common failure points of your Mercedes engine is the single most effective way to avoid a costly surprise. Use this index to identify your engine, learn its weak spots, and take preventative action early. If you already have a symptom, use the Symptom Hub to diagnose and then book a diagnostic with a vetted specialist.
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