BMW M4 M4 Cabrio common faults.

2014–2017, convertible, petrol, 431 HP.

The fault list covers: S55B30 engine.

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5 fault write-ups. 4 important. 17 recalls.

If you know the year, pick it. Faults for other years drop out of the list.

Before you buy

Known faults

4 important faults

critical1

Crank hub: only friction holds it, and if it slips the valve timing is lost

critical

The multi-part crank hub is held in place only by the clamping force of the crankshaft bolt and the friction between the mating surfaces. There is no key and no splined connection, so there is no mechanical constraint either. Under sustained high load, at high torque, the hub can slip, and the valve timing then loses its reference to the crankshaft.

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The symptom is a drivetrain malfunction message on the dashboard, the engine management light, uneven running, difficult starting and limp mode. A camshaft or crankshaft timing code appears in the fault memory, and the two together are the most telling. If the timing moves far, the valve and the piston can meet, and that is internal engine damage.

Not every example is affected: many engines run without trouble throughout. The risk is higher on tuned and track-driven cars, because the load there is greater, but standard condition does not rule it out either. The fault occurs from 60 000 kilometres.

The solution is a pinned conversion: precisely drilled pins give a mechanical connection in place of the friction. The part is around 800 pounds, and 1950 pounds with fitting. One thing is worth knowing: this fault belongs to the S55 engine, and the N55, the B58 and the S58 are not affected.

above 60,000 km

What to check

Have the fault codes read and look for camshaft and crankshaft timing codes
Ask whether there has been a drivetrain malfunction message on the dashboard
Start it cold: difficult starting and uneven running belong here

2 more steps in the write-up

expensive3

Oil cooler under the front spoiler: one stone punctures it

expensive

The engine oil is cooled by an air-to-oil cooler, and it sits under the front spoiler, perpendicular to the ground. There is no protection in front of it, so stones thrown up hit it directly. The core of the factory cooler is of tube-and-fin construction, and that structure is sensitive: even a smaller stone can puncture it, and the oil then runs out quickly.

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This is not wear but an impact, so the mileage says little here: it is reported from 40 000 kilometres, but it can happen at any time. There is no advance sign: a slow leak does not start, instead the oil pressure warning and the streak of oil under the car come suddenly. At that point you have to stop immediately.

There are two directions for the repair. There is an aftermarket cooler that comes with a removable and replaceable rock guard. The other direction is stronger construction: a bar-and-plate aluminium cooler stands up better to flying gravel, and goes into the same factory location. The suppliers themselves argue that the factory part is easily damaged.

above 40,000 km

What to check

Bend down under the front spoiler and look at the oil cooler: the fins should not be dented
Look for traces of oil under the cooler and under the car
Watch the oil pressure warning light after start-up and while driving

3 more steps in the write-up

S55: connecting rod bearings that wear early

expensive

The connecting rod bearings wear from as little as 60,000 kilometres, which is early even for an engine of this output. The debris shows up as metal particles in the oil.

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The symptoms are knocking from the engine block, a metallic sheen in the oil and the oil pressure warning light. If a bearing runs, the crankshaft is damaged too and the repair is an engine rebuild. The bearing shell size and clearance are the same on the N54 and the N55, with the same factory part numbers. The S55, however, manages the oil pressure better, so the trouble is rarer on it than on its smaller siblings.

above 60,000 km

What to check

Listen to the engine under load when warm: a deep knock means a bearing fault
Look at the condition of the oil: a metallic sheen points at wear
Ask for an oil analysis if possible: the metal content is measurable there

2 more steps in the write-up

Valvetronic: oil in the sensor connector, a worn eccentric shaft

expensive

Valvetronic adjusts the lift of the intake valves, and an eccentric shaft does that work. Three parts can fail here, at very different prices, and their symptoms are nearly identical.

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The sensor is usually the first to give up: oil leaks past its seal into the connector, and the oil corrupts the signal the engine control unit depends on. From then on the control unit gets no reliable position feedback, cannot set the valve lift precisely, and switches to a protective strategy. The fault code in this case is a plausibility fault, 2A67 or 2A6B: the control unit does not consider the position signal credible.

The eccentric shaft itself can also wear out or seize, and there are several causes for that: lack of lubrication from oil sludge and skipped oil changes, wear of the bearings, a system driven on with a failed actuator motor, and overheating and oil contamination in the cylinder head. It is reported from 150 000 kilometres.

The symptom is similar in all three cases: an unstable idle, stumbling and long cranking at a cold start, a check engine light that comes on and goes out on its own, lack of power or limp mode, inconsistent throttle response, and misfires cylinder by cylinder. A clicking, binding noise from the engine bay points to a seizing shaft.

The misdiagnosis is common, because the symptom shows up at combustion, so coils and spark plugs are suspected first, while the fault is in the air control. The condition of the shaft can only be established after the valve cover has been removed and it has been inspected. The sensor connector, though, is worth opening up first: if it is oily, that is the far cheaper route.

above 150,000 km

What to check

Open up the connector of the eccentric shaft sensor: an oily connector means the cheaper fault
Watch the revs at idle: an unstable idle and misfires cylinder by cylinder belong here
Start it cold: stumbling and long cranking are symptoms

3 more steps in the write-up

cheap repair1

Plastic charge pipe: it goes brittle and cracks at the throttle body

cheap repair

The maker builds the charge pipe out of plastic, and the coupler at the throttle body is the critical point. The material goes brittle from heat cycles, from boost pressure and from the heat of the engine bay, and then it cracks. Three things coincide here: the moulded coupler carries both pressure and movement, the vibration of the engine arrives here through the throttle body, and the spot gets continuous heat load. The crack starts on the inner radius of the coupler. The symptom is a loss of pressure under load: the engine pulls cleanly at part throttle but flattens out at full throttle, and a hissing noise is audible from the engine bay at the same time. A yellow drivetrain warning comes with it, which often disappears after a restart, and sometimes a brief limp mode. One thing is worth knowing: a clean fault memory does not rule the crack out. The pipe has no sensor of its own, so the control unit can only log a boost pressure fault, and the leak is intermittent, appearing only under load. At a viewing two things are visible without tools. On the inner radius of the coupler the hairline crack sometimes comes with dark staining, because the oil mist in the boost air escapes through it. For the same reason a greasy, dark ring can appear at the joint of the coupler. The crack is reported above 80 000 kilometres, and replacing the pipe costs between 100 and 400 euros, because the part itself is not expensive. The most common misdiagnosis against that is replacing the turbocharger, which costs an order of magnitude more, and a pressure test protects against it. The factory repair is the same plastic part, which can crack again at a similar mileage; replaced with an aluminium pipe this failure mode disappears, and the driveability does not change.

above 80,000 km100–400 EUR

What to check

Look at the inner radius of the coupler at the throttle body: the hairline crack sometimes comes with dark staining
Look for a greasy, dark ring at the joint of the coupler
On a motorway slip road at full throttle watch for the loss of pressure and the hissing noise

2 more steps in the write-up

Official recall17 recallsShow

The manufacturer fixes these for free at a franchised dealer. Ask with the VIN whether it was done.

Most recent: 7 July 2026

SR/02180/26Safety recallFire7 July 2026 · EU Safety Gate

The RSW22 starter with reinforced water tightness (RWT) may experience increased abrasion of the magnetic contact, causing deposits to build up at the lowest point inside the relay. These deposits may increase relay contact resistance, leading to starting failures or short circuits. If a short circuit occurs, either when attempting to start the vehicle or while driving due to vibration-related movement of the deposits, it could cause a thermal event and increase the risk of fire. The product does not comply with the Regulation on the approval and market surveillance of motor vehicles and their trailers, and of systems, components and separate technical units intended for such vehicles.

Remedy: Type of economic operator taking notified measure(s): Manufacturer Category of measure(s): Recall of the product from end users Date of entry into force: 07/07/2026

We could not check this: model year. The authority's notice

SR/00551/26Safety recallFire30 January 2026 · EU Safety Gate

The failure concerns the RSW22 starter, type RWT (reinforced for watertightness). Increased abrasion of the magnetic contact can lead to the formation of deposits at the lowest point of the relay interior. This in turn can increase the resistance of the relay contact, causing accidental ignition or even short circuits, possibly leading to a thermal reaction and fire. The product does not comply with the Regulation on the approval and market surveillance of motor vehicles and their trailers, and of systems, components and separate technical units intended for such vehicles.

Remedy: Type of economic operator taking notified measure(s): Manufacturer Category of measure(s): Recall of the product from end users Date of entry into force: 30/01/2026

We could not check this: model year. The authority's notice

SR/00568/26Safety recallFire30 January 2026 · EU Safety Gate

Remedy: Type of economic operator taking notified measure(s): Manufacturer Category of measure(s): Recall of the product from end users Date of entry into force: 30/01/2026

We could not check this: model year. The authority's notice

A12/00868/23Safety recallInjuries30 March 2023 · EU Safety Gate

The airbag may deteriorate over time, and if deployed, excessive internal pressure may cause the inflator body to burst and metal fragments could pass through the cushion material causing injury to occupants. The product does not comply with the Regulation on the approval and market surveillance of motor vehicles and their trailers, and of systems, components and separate technical units intended for such vehicles.

Remedy: Type of economic operator taking notified measure(s): Manufacturer Category of measure(s): Recall of the product from end users Date of entry into force: 30/03/2023

We could not check this: model year. The authority's notice

A12/01930/23Safety recallInjuries29 June 2021 · EU Safety Gate

The propellant in the driver airbag can deteriorate due to high humidity and temperature variations. In the event of an accident in which the airbag deploys, this could result in fragments from the inflator casing coming loose and injuring the vehicle’s occupants. The product does not comply with the Regulation on the approval and market surveillance of motor vehicles and their trailers, and of systems, components and separate technical units intended for such vehicles.

Remedy: Type of economic operator taking notified measure(s): Manufacturer Category of measure(s): Recall of the product from end users Date of entry into force: 29/06/2021

We could not check this: model year. The authority's notice

A12/00134/21Safety recallFireno date · EU Safety Gate

The fuel injectors may not have been equipped with a decoupling element. This could result in a vibration fracture at the soldering point of the high-pressure fuel rail. Consequently, fuel could leak into the engine compartment, increasing the risk of fire.