Mercedes-Benz SLC R172
Weaknesses, engine ratings and buying advice
The SLC is the renamed SLK R172 — from 2016 with a new badge, subtly refreshed design, and a streamlined engine range. Technically identical to the late SLK R172 but with updated infotainment options.
The M274 1.6–2.0L turbo at 115 to 180 kW covers SLC 180, SLC 200, and SLC 300. The M274 is the most modern engine — more efficient and refined than the old M271 supercharged. The OM651DE22 diesel at 150 kW in the SLC 250 d remains for long-distance drivers. The M276 V6 at 270 to 287 kW in the AMG SLC 43 is the sporty crown — no V8, but a BiTurbo V6 with enough power and refined sound.
The Vario roof with Magic Sky Control remains the unique feature. The technology is mature and less failure-prone than earlier generations. Rust is not a concern.
The SLC was discontinued in 2020 with no direct successor, making it a potential long-term collector car, especially the AMG SLC 43.
Test-drive checklist: Test Magic Sky. M274: cold-start smoothness. AMG SLC 43: V6 BiTurbo sound must be symmetrical and clean. Test chassis on a spirited road — the SLC sits lower than the GLA and handles more agile.
2026 market: Between $24,200 and $49,500. AMG SLC 43 from $38,500. Prices stable — end-of-line effect.
Insider pick: AMG SLC 43 (M276, 287 kW) — the last compact Mercedes roadster, well-equipped with appreciation potential.
390 PS
AMG SLC 43 · Benzin
390 hp Facelift — The Last and Best SLC
Legendary!120–204 PS
2.1L Diesel Diesel
7 weaknesses
Stay Away!Engine Overview
The Mercedes-Benz SLC R172 is available with 5 engine variants — from 120 to 435 hp.
Most widespread Mercedes four-cylinder diesel, aluminium block with steel liners. Simplex timing chain sits at the rear of the gearbox and stretches from 120,000 km — chain tensioner recall covered 100,000+ vehicles in Germany (February–November 2014 production). Engine was part of the Mercedes emissions scandal: illegal thermal window defeat device; recall software in some vehicles actually worsened NOx values. Piezo injectors in the 250 CDI were never updated — remains an ongoing risk. Well-maintained examples with solenoid injectors and short oil-change intervals can reach 400,000 km.
- !! Chain Tensioner Seal Leaking — Recall
Over 100,000 vehicles recalled: the chain tensioner seal leaks, allowing engine oil to drip onto the exhaust system and potentially ignite.
Symptoms: Dropping oil level, oil smell from engine bay, oily deposits under the vehicle, possible oil fire - !! Timing Chain Stretch (Simplex Chain) from 150,000 km
The OM651 uses a simplex timing chain. With short-trip driving and overdue oil change intervals the chain stretches.
Symptoms: Light rattling noise on cold start from the rear of the engine, no fault code stored - !! Piezo Injector Faults from 80,000 km
Same Delphi piezo injector problems as in the DE18: 220 CDI and 250 CDI variants affected. Mercedes replaced them with solenoid injectors as part of a service action.
Symptoms: Vibrations and rough running especially under acceleration, elevated fuel consumption
+ 4 more engine weaknesses + vehicle weaknesses
Four-valve V6 in two basic variants: 3.5L naturally aspirated (DES 35, 185–225 kW) with direct injection and stratified charge — refined, linear, no classic naturally aspirated feel. And the 3.0L BiTurbo family (DEH 30 LA, 245–295 kW) with Nanoslide coating, twin turbochargers and water-air charge air cooler. The BiTurbo sings sonorously from 2,500 rpm and screams at the top — exceptional for a V6. Weak points: timing chain wears early when oil change intervals are pushed. Oil cooler in the V-block doesn't seal forever. Camshaft solenoids leak. On the 3.5L stratified-charge variant add NOx sensor failures from short-trip use. Early DES 35 (2011–2013) had piston slap issues. The BiTurbo unit with Nanoslide is considered more robust. Maintained with short oil change intervals (10,000–12,000 km) the engine easily lasts beyond 200,000 km.
- !! Oil cooler leaking in the V-block from 120,000 km
Known weak point: the oil cooler gasket in the V-block of the M276 ages and starts leaking. Repair is extremely labour-intensive because the engine must be partially disassembled — cost €1,700–3,800.
Symptoms: Oil spots under the vehicle, rainbow sheen on wet road, dropping oil level, oil smell - !! Camshaft adjuster leaking — wiring harness contaminated from 100,000 km
Known damage pattern on all newer Mercedes engines: solenoid valves leak, oil migrates into the wiring harness. First the lambda sensors die, then the ECU. Repair documented up to €1,970.
Symptoms: Check engine light with camshaft fault code, lambda sensor failure, oil film on connectors, in extreme cases ECU failure - !! Piston slap (early 3.5L variants) from 150,000 km
On early M276 DES 35 (build years 2011–2013) pistons can loosen due to cylinder bore wear. Knock noise on cold start, worst case engine damage.
Symptoms: Clacking and knocking on cold start from the engine area, getting louder over time, rough idle when cold
+ 7 more engine weaknesses + vehicle weaknesses
Evolved four-cylinder turbo with direct injection and piezo injectors. Significantly less prone to timing chain problems than the M271, but not immune. Electric thermostat tends to fail early — always replace as complete OEM unit. Early DE20 LA units (2015–2016) have a piston pin manufacturing tolerance issue — short block replacement required if symptom arises. Camshaft solenoids (Y49/1, Y49/2, pre-2014) prone to leaks. Oil changes every 10,000 km with MB 229.5 recommended.
- !! High-Pressure Pump Faulty or Noisy from 120,000 km
The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.
Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087 - !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km
On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.
Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure - !! Piston Pin Knock (2015–2016 units) from 60,000 km
Early M274 DE20 LA units (2015–2016) have a manufacturing tolerance issue with excessive piston pin clearance. Blue smoke and oil consumption up to requiring short-block replacement.
Symptoms: Metallic knocking from engine block, blue-grey exhaust smoke, increased oil consumption
+ 4 more engine weaknesses + vehicle weaknesses
Evolved four-cylinder turbo with direct injection and piezo injectors. Significantly less prone to timing chain problems than the M271, but not immune. Electric thermostat tends to fail early — always replace as complete OEM unit. Early DE20 LA units (2015–2016) have a piston pin manufacturing tolerance issue — short block replacement required if symptom arises. Camshaft solenoids (Y49/1, Y49/2, pre-2014) prone to leaks. Oil changes every 10,000 km with MB 229.5 recommended.
- !! High-Pressure Pump Faulty or Noisy from 120,000 km
The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.
Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087 - !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km
On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.
Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure - !! Piston Pin Knock (2015–2016 units) from 60,000 km
Early M274 DE20 LA units (2015–2016) have a manufacturing tolerance issue with excessive piston pin clearance. Blue smoke and oil consumption up to requiring short-block replacement.
Symptoms: Metallic knocking from engine block, blue-grey exhaust smoke, increased oil consumption
+ 4 more engine weaknesses + vehicle weaknesses
Evolved four-cylinder turbo with direct injection and piezo injectors. Significantly less prone to timing chain problems than the M271, but not immune. Electric thermostat tends to fail early — always replace as complete OEM unit. Early DE20 LA units (2015–2016) have a piston pin manufacturing tolerance issue — short block replacement required if symptom arises. Camshaft solenoids (Y49/1, Y49/2, pre-2014) prone to leaks. Oil changes every 10,000 km with MB 229.5 recommended.
- !! High-Pressure Pump Faulty or Noisy from 120,000 km
The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.
Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087 - !! Camshaft Adjuster Leaks — Oil in Wiring Harness from 100,000 km
On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.
Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure - !! Piston Pin Knock (2015–2016 units) from 60,000 km
Early M274 DE20 LA units (2015–2016) have a manufacturing tolerance issue with excessive piston pin clearance. Blue smoke and oil consumption up to requiring short-block replacement.
Symptoms: Metallic knocking from engine block, blue-grey exhaust smoke, increased oil consumption
+ 4 more engine weaknesses + vehicle weaknesses
Vehicle Weaknesses
| Weakness | Cost | |
|---|---|---|
| Vario roof leaking -- water ingress in rain As with the predecessor SLK R171, the SLC R172 (facelift from 2016) also develops leaks at the vario roof when seals age or become brittle through UV exposure. The sealing of the metal folding roof in the area of the roof rails requires regular maintenance. Symptoms: Damp interior after rain, water stains on headliner, musty smell from 60,000 km | High |
Test Reports
TÜV Report 2024
The SLC R172 continues the above-average TÜV result of the SLK it replaced and performs well in its age group.
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Known Problems and Issues +
A total of 30 weaknesses have been documented for the Mercedes-Benz SLC R172 (2016–2020) — 24 engine-related and 6 vehicle-related. One problem engine: OM651DE22 (2.1L Diesel). Typical issues affect Body, Suspension, Electronics, Interior.
SLC (OM651DE22, 2016–2017) — Stay Away!: Chain Tensioner Seal Leaking — Recall, Timing Chain Stretch (Simplex Chain), Piezo Injector Faults. Power: 204 PS.
SLC (M274, 2016–2020) — Be Careful: High-Pressure Pump Faulty or Noisy, Camshaft Adjuster Leaks — Oil in Wiring Harness, Piston Pin Knock (2015–2016 units). Power: 156 PS.
SLC (M274, 2016–2020) — Be Careful: High-Pressure Pump Faulty or Noisy, Camshaft Adjuster Leaks — Oil in Wiring Harness, Piston Pin Knock (2015–2016 units). Power: 184 PS.
SLC (M274, 2016–2020) — Be Careful: High-Pressure Pump Faulty or Noisy, Camshaft Adjuster Leaks — Oil in Wiring Harness, Piston Pin Knock (2015–2016 units). Power: 245 PS.
SLC (M276, 2016–2018) — Be Careful: Oil cooler leaking in the V-block, Camshaft adjuster leaking — wiring harness contaminated, Piston slap (early 3.5L variants). Power: 367 PS.
SLC (M276, 2018–2020) — Be Careful: Oil cooler leaking in the V-block, Camshaft adjuster leaking — wiring harness contaminated, Piston slap (early 3.5L variants). Power: 390 PS.
What to watch out for with the Mercedes-Benz SLC? See the detailed listing of all engine and vehicle weaknesses in the sections above.
Frequently Asked Questions
What problems and weaknesses does the Mercedes-Benz SLC R172 have? +
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Which Mercedes-Benz SLC R172 engine is the most fun? +
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Last updated: February 2026 · All information without guarantee