Mercedes-Benz M156 engine: known problems

Owner/reviewer-reported: worn cam lifters wear the camshaft lobes, causing a ticking or rough running; the cure is a top-end rebuild with new cams and lifters. A used-car review for Australian buyers says parts may need replacing by about 150,000 km and that 5,000 km oil changes help. UK guides call the fault rare.

Documented M156 fault on early engines: the original head bolts can corrode or stretch and break, letting coolant into the oil or combustion chamber. Reported warning signs are a low coolant light, misfires and a check-engine lamp. A broken bolt loads the others, so failure can cascade. Enthusiast and parts-supplier sources put the affected engines as those below engine number ending 60 060658 (roughly 2006 to early 2010 builds), and an Australian reference site lists head bolt failure for the CLS63 AMG and other M156 cars. Whether a given car has been updated is not shown by the build date alone.

Early M156 engines (reported on 2008-2011 builds) can snap cylinder head bolts, which leads to head gasket failure and engine damage. UK and Australian guides describe it as rare, and one says it is more common in the USA than Europe. Mercedes is reported to have replaced engines under warranty. An owner forum claim that 2012 and later engines have revised parts and avoid the fault is a single unverified post, so do not rely on year alone. Signs: coolant loss, white smoke, overheating, misfire.

Injectors can stick open and flood a cylinder with fuel. In the worst case hydraulic lock bends or breaks a conrod. Two guides mention it; one suggests replacing injectors ahead of failure if the budget allows.

Early M156 engines can suffer cylinder head bolt failure. The torque-to-yield bolts can stretch and snap, and one failure overloads its neighbours. Coolant and oil then cross over, giving repeated low-coolant warnings, a high oil level, white exhaust smoke, a rough idle and a check-engine light; in a severe case the engine hydro-locks and is destroyed. Mercedes' April 2011 bulletin LI01.30-P-051567 covers engine numbers up to 1569xx 60 060658 (built 2006 to the first half of 2010). The W212 only went on sale in late 2009, so only the earliest AU cars sit inside the engine-number range; some owners believe later cars got revised bolts, but this is not confirmed by the bulletin we found.

Premature wear of the intake camshaft lobes and hydraulic lifters is the best-known M156 fault; the lobe can wear through the lifter. A cold-start ticking is the early sign. Frequent oil changes with the right viscosity are the main prevention.

W221 cars with ABC had an Australian recall for the front strut ball joint (see Recalls) and are prone to leaking air bellows/hydraulic components with age; a UK guide advises checking ride height at every corner, since leaks overwork the pump and let the car sink. Owner-reported: warning lights and a lowered corner are the usual signs.

Owner-reported and documented by an Australian recall: Active Body Control struts, lines and the pump can leak under high pressure, and a warning appears in the cluster. A September 2008 Australian recall (PRA 2008/10321) covered faulty front-axle acceleration sensors in ABC on R230 SLs, which can cause random body vibrations; we could not verify whether it covers the SL63. Replacement of a strut needs the system refilled and bled.

Owner-reported: the camshaft adjusters (intake worst) lose hydraulic pressure and rattle at cold start, then at any revs. A service bulletin is said to cover it.

Owner-reported / parts-supplier sourced: valve cover, cam solenoid cover and oil filter housing gaskets commonly leak, and the crankcase breather diaphragm or hose can deteriorate, causing oil burning, misfires, smoke and fuel-trim codes. Leaks can contaminate the alternator, belt and hoses.

Owner-reported: air springs, height sensors or the compressor (reported to fail from a degraded electrical connector) let the car sink at one or both ends, often overnight, with a suspension malfunction message. Single-owner reports, not a documented rate.

Owner/reviewer-reported: a rattle for a second or two at cold start from worn cam adjusters (phasers). A single Australian used review gives the dealer price quoted; we could not confirm it elsewhere. Ignore a cold-start rattle and the camshaft and chain wear follow.

Cracked or leaking intake manifolds cause a rough idle (a warning sign cited in UK and Australian guides). Valve cover oil leaks are also reported by owners. Aftermarket kits exist for both.

A UK buying guide says the Series II front bumper restricts airflow to the radiators, so the gearbox can overheat under hard driving. Its suggested fix is the Black Series cooling upgrade with a Black Series bumper, and it says the parts could be expensive. A second UK guide calls the transmission extremely reliable and reports no MCT faults. Single-source on the overheating.

The car's weight and power wear front pads, discs and rear tyres quickly. Australian used-car review says AMG brakes are very expensive to maintain and many owners fit aftermarket systems. Performance Pack and 507 cars have larger or composite front discs that cost more again.

Official: a 2010 recall covered fluid loss at the power steering pump high-pressure line connection on W204/W212/C207 cars (see Recalls). Owner-reported: a power steering hose can chafe through the sump.

Australian owners report ads with made-up power figures (a suspicious '380kW' claim on a pack car and a 'Black Series' that was not one). The pack is a factory option on the standard C63 with 358kW and the engine and brake changes listed above.

Owner-reported: the air struts and springs eventually fail, giving a sagging corner or a warning message, and owners describe it as a matter of when. Fixes discussed are replacement air struts or a coil-over conversion.

If the air-intake drain valve blocks, water can reach the fuse box and cause electrical faults.

Owner-reported: some cars hesitate on upshifts in manual mode at high throttle, and one reported case had the conductor plate/valve body replaced after the car would not select drive. Others report no gearbox trouble at all.

Owner-reported (from a UK buyer's guide): M156 injectors can stick open, washing the bores or in the worst case hydraulically locking a cylinder.

Reported by a parts retailer: the centre mounting plate that holds the twin throttle bodies in the magnesium intake manifold deteriorates, causing a rough idle. A full genuine manifold is expensive and can be back-ordered.

Reported by a parts retailer: the plastic drive belt pulleys with pressed-in bearings fail and can damage the belt, and the belt can in turn damage the thermostat's coolant breather port.

A UK guide says shifts were not always smooth on pre-facelift cars, linked to the valve body and conductor plate electronics of the 7G-Tronic.

Owner-reported: roof cylinders can leak, the pump can fail and microswitch faults can stop the roof opening or closing.

Owner-reported: some 2009 cars have hard or jerky shifts on cold start and downshifts. One owner had the valve body and wet clutch replaced without a clear result, another reported a dealer visit fixed it. No official bulletin or cost was found.

Moisture can affect the crank sensor, giving rough idle, hard starting or hesitation. Listed among reported W211 AMG faults on a recall-and-fault index for Australian cars.

Owner-reported: valve cover, cam adjuster housing cover and oil cooler return line O-rings seep. Owners call it minor.

UK guide: valve cover, camshaft solenoid cover and oil filter housing gaskets leak, the crankcase breather valve diaphragm and hose deteriorate, and the magnesium intake manifold and idler pulley can fail.

Owner-reported (Australian and UK guides): a faulty parking brake switch triggers a dash warning and brake failure message; intermittent A/C from a fan/blower fault and sunroof wind noise from a failed seal also appear, plus control-module electrical faults generally.