BMW 3 Series: N20 2.0T turbocharger wastegate flap rattle and underboost (320i/328i)
N20 2.0T turbocharger wastegate flap rattle and underboost (320i/328i) is a common engine fault on the BMW 3 Series on the 2012–2018 cars, and we rate it major. Putting it right costs $1,100 to $4,800 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 88 documented faults on the BMW 3 Series.
- Vehicle
- BMW 3 Series
- Engine
- N20
- Years
- 2012–2018
- Fuel
- petrol
- System
- Engine
What you are looking at
No photograph available
What goes wrong
The N20's turbocharger controls boost with a small exhaust flap on an arm inside the turbine housing. The bush the arm runs in wears oval, so the flap knocks against its seat at idle and light load and makes a fast metallic clatter that most people mistake for a loose heat shield. Left alone the flap stops sealing, boost control drifts out of range and the car drops into limp mode with an underboost fault, usually the first time you really need the power. BMW has no separate repair part, so the official answer is a complete turbocharger — independent specialists rebuild the flap assembly for considerably less.
What you would notice
- Fast, light metallic chatter low on the exhaust side at idle, worst when warm
- Rattle that vanishes the moment you touch the throttle and returns as revs drop
- Sudden flat spot and a drop into limp mode on a hard climb or overtake
- Engine warning light with a boost or charge-pressure complaint
How to check it
Where to look. Turbocharger mounted to the exhaust manifold on the right-hand side of the engine, low down towards the bulkhead, under the heat shield.
Stand at the front of the car with the bonnet up while the engine idles warm and listen low down on the exhaust side for a fast, light metallic chatter — blip the throttle and it should disappear, then come back as the revs fall. Ask the seller to hold a fast idle for you while you listen, and compare that against how the car sounds from stone cold. On the test drive use full throttle in third gear at least twice, up to about 4,000 rpm, and watch for a sudden flat spot, a warning light, or a reduced-power message. A car that is only ever driven gently can hide an underboost fault, so it has to be worked before you believe it. Ask whether the turbocharger has been replaced or rebuilt and get the invoice.
What it costs to put right
$1,100 to $4,800 at New Zealand independent workshop rates. That is for this job on its own, not for the car.
Ask the seller
- “Has the turbocharger ever been replaced or rebuilt?”
- “Has the car ever gone into limp mode or shown a reduced-power message?”
- “How often has the oil been changed, and with what grade?”
Now check the BMW 3 Series you are actually looking at
Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.
Where this comes from
- BIMMERPOST F30 forum thread — 'N20 Wastegate rattle :('
- MRI Auto Diagnostics service document — 'Wastegate Replacement, 2013 BMW 328i Sedan (F30) L4-2.0L Turbo (N20)'
- MS Motor technical article — 'BMW N20 Turbo Wastegate Rattle: Causes, Codes & Fix'
- BimmerShops — E84 X1 common problems (turbocharger wastegate failure and boost pressure faults)
BMW 3 Series buyer questions
Is n20 2.0t turbocharger wastegate flap rattle and underboost (320i/328i) serious on a BMW 3 Series?
We rate it major and common on the BMW 3 Series. The N20's turbocharger controls boost with a small exhaust flap on an arm inside the turbine housing. The bush the arm runs in wears oval, so the flap knocks against its seat at idle and light load and makes a fast metallic clatter that most people mistake for a loose heat shield. Left alone the flap stops sealing, boost control drifts out of range and the car drops into limp mode with an underboost fault, usually the first time you really need the power. BMW has no separate repair part, so the official answer is a complete turbocharger — independent specialists rebuild the flap assembly for considerably less.
How much does it cost to fix on a BMW 3 Series?
$1,100 to $4,800 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.
Which BMW 3 Series years are affected?
Our research records this fault on the 2012–2018 BMW 3 Series. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.
How do I check for it before I buy?
Stand at the front of the car with the bonnet up while the engine idles warm and listen low down on the exhaust side for a fast, light metallic chatter — blip the throttle and it should disappear, then come back as the revs fall. Ask the seller to hold a fast idle for you while you listen, and compare that against how the car sounds from stone cold. On the test drive use full throttle in third gear at least twice, up to about 4,000 rpm, and watch for a sudden flat spot, a warning light, or a reduced-power message. A car that is only ever driven gently can hide an underboost fault, so it has to be worked before you believe it. Ask whether the turbocharger has been replaced or rebuilt and get the invoice. Look here: Turbocharger mounted to the exhaust manifold on the right-hand side of the engine, low down towards the bulkhead, under the heat shield.