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BMW common faults and how to fix them

Faults that are well known on BMW models we hold manuals for: what the owner notices, what causes it, and the pages in our manuals that cover the repair.

N47 timing chain failure: 320d, 118d, 120d and 520d (2007 on)

Symptoms

A rattle or whine from the back of the engine, near the gearbox, that is loudest at idle or when the engine is cold and gets worse over time. It is often heard as a whine from the bulkhead. If the chain breaks, the engine cuts out while driving and will not restart, and the valves usually hit the pistons.

Cause

The N47 2.0 diesel, used in the 118d, 120d, 123d, 318d, 320d, 520d and X3 2.0d, has its timing chains at the flywheel end of the engine. The chains, guides and tensioner wear and the chain stretches. Long oil change intervals are often blamed. Wikipedia notes reports of N47 timing chain failures on BMW diesels built up to 2015, and that a failure can mean a new engine.

Fix

Treat a rattle from the rear of the engine as urgent. N47 timing chain replacement covers the chains, guide rails, tensioner and the sprockets where worn. Because the chains sit behind the BMW 320d timing chain cover at the rear, BMW's procedure starts with removing the engine, flywheel, cylinder head and oil sump. That makes it a long job, and a failed chain often means a replacement engine instead. The N47 timing chain tensioner has its own procedure. Change the oil and filter at short intervals afterwards.

Repair instructions on this site

Sources: Wikipedia — BMW N47; BMW repair instructions 11 14 110.

BMW swirl flaps: M47 2.0 diesel in the 320d, 120d and 520d

Symptoms

Often there is no warning. A swirl flap or its spindle breaks off inside the intake manifold, is drawn into a cylinder and hits the piston and valves. The engine then knocks heavily, smokes and loses power, and the turbocharger can be damaged by the debris. Before that point some engines show rough running or an EGR or intake fault code.

Cause

The updated M47 diesel (M47TU, then M47T2) brought small flaps in the intake manifold, one per cylinder, to create swirl at low engine speeds. Their spindles wear and the flaps work loose. Wikipedia records that failures were common enough for specialist BMW magazines to cover the problem, and that BMW fitted stronger flaps and larger spindles in 2006. The engine is used in the E46 318d and 320d, the E87 118d and 120d, the E90 and E91 318d and 320d, the E60 and E61 520d and the X3 2.0d.

Fix

Remove the BMW 320d swirl flaps with the intake manifold and check each flap and spindle for play or missing pieces. Worn flaps are replaced with the later type. Some owners choose a swirl flap delete with blanking plugs instead, but that can affect emissions and fault codes. If a flap has already gone into the engine, the cylinder head comes off for inspection.

Repair instructions on this site

Sources: Wikipedia — BMW M47.

N54 HPFP failure: 335i, 135i and 535i high-pressure fuel pump

Symptoms

Long cranking before the engine starts, especially when warm. The engine goes into reduced power with a warning message, hesitates under acceleration or stalls. In the worst cases it cuts out on the move.

Cause

The N54 3.0 twin-turbo is a direct-injection engine. A pump driven by the camshaft raises fuel pressure for the piezo injectors. Some pumps fail and pressure drops. In the United States this led to a class action, a recall in October 2010 covering 2007–2010 cars, and an extended warranty of 10 years or 120,000 miles on the pump. BMW also extended the injector warranty and brought in a revised injector.

Fix

Read the fault memory and check the low-pressure and high-pressure fuel readings before replacing parts, as a weak in-tank pump or a faulty N54 high-pressure fuel sensor can cause similar symptoms. If the N54 HPFP is at fault, replace it with the latest part. Pressure in the high-pressure system must be released as the procedure describes, and the fuel lines are replaced, not reused. Check whether a recall or warranty extension applies before paying for a 335i high-pressure fuel pump replacement.

Repair instructions on this site

Sources: Wikipedia — BMW N54; NHTSA recall, October 2010 (BMW high-pressure fuel pump).

N54 wastegate rattle: 335i, 135i and 535i turbochargers

Symptoms

A metallic rattle or buzzing from the turbochargers, usually heard at low engine speed and when lifting off the throttle, and often worse when cold. As the wear increases the turbos may not hold boost, giving low power and boost fault codes.

Cause

Each of the two N54 turbochargers has a wastegate flap that opens to limit boost. Its pivot runs in a bushing in the hot turbine housing. The bushing wears early, so the flap and its linkage have play and rattle against their stops. Wikipedia records that BMW extended the warranty on wastegate faults in the United States to 8 years or 82,000 miles because of this.

Fix

First rule out the simpler causes: a loose heat shield, or a vacuum unit (wastegate actuator) that has lost its vacuum, which gives low boost without wear in the turbo. Wear in the wastegate bushing itself is not serviced separately, so the N54 turbo on that bank is replaced. The front turbo and rear turbo have separate procedures, and the job usually means lowering parts of the exhaust and intake.

Repair instructions on this site

Sources: Wikipedia — BMW N54.

N43 injector, coil and timing chain faults: 118i, 120i, 318i and 320i (2007–2011)

Symptoms

The engine misfires, runs roughly or shows the engine light, from a failed injector or ignition coil. Separately, a rattle from the timing chain at start-up. In worse cases the oil pressure warning comes on, because broken pieces of chain guide have blocked the oil pick-up.

Cause

The N43 is BMW's direct-injection, lean-burn 4-cylinder petrol engine, used in the 116i, 118i and 120i, the 316i, 318i and 320i, and the 520i. Wikipedia lists its main faults: problems with the injectors, coil packs and the NOx sensor, plus plastic cam chain guides that break, with the debris blocking the oil strainer and starving the engine of oil.

Fix

For a misfire, swap the coil to another cylinder to see if the fault follows it, then check the ignition coils and test the N43 injector on that cylinder. Treat chain noise or an oil pressure warning as urgent and stop the engine. N43 timing chain replacement includes the guides, and the oil sump comes off so the pick-up strainer can be cleared of debris.

Repair instructions on this site

Sources: Wikipedia — BMW N43.

Repair instructions for every BMW model: BMW workshop manuals