BMW 1 Series: N45/N46 Valvetronic eccentric shaft sensor and motor failure (E87 116i/118i/120i)
N45/N46 Valvetronic eccentric shaft sensor and motor failure (E87 116i/118i/120i) is a common engine fault on the BMW 1 Series on the 2004–2011 cars, and we rate it major. Putting it right costs $350 to $1,700 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 50 documented faults on the BMW 1 Series.
- Vehicle
- BMW 1 Series
- Engine
- N45 / N46
- Years
- 2004–2011
- Fuel
- petrol
- System
- Engine
What you are looking at
No photograph available
What goes wrong
The N45 and N46 four-cylinders meter airflow with Valvetronic — an electric motor turning an eccentric shaft to vary how far the inlet valves open — and a single position sensor reads that shaft. Oil and combustion soot creep down the sensor's connector and coat its face, the engine management loses confidence in the valve-lift signal, and the car drops into a limp mode with almost no power. There is no second sensor to fall back on, so one dirty sensor is enough to strand the car. Sometimes it is only the sensor and its O-ring; on higher-mileage cars the eccentric-shaft motor is worn or the shaft is binding, which is a far bigger bill.
What you would notice
- Sudden loss of power with the engine warning light on, often shortly after a cold start
- Long cranking or an intermittent refusal to start
- Rough, hunting idle that comes and goes
- Warning light that clears on a restart and returns days later
- Engine feeling flat and breathless above 3,000 rpm
How to check it
Where to look. Top of the cylinder head under the plastic engine cover — the sensor screws into the head at the front, with the eccentric-shaft motor mounted alongside it.
Start the engine from cold and let it idle, because the fault most often shows in the first minute — a car already warmed up before you arrive deserves a second visit at a time you choose.
Watch the engine warning light through the whole test drive, and specifically after a hot restart: stop, switch off, wait a minute and start it again.
Listen for a hesitant, drawn-out crank rather than an instant catch.
Ask the seller whether the car has ever gone into limp mode, and whether the Valvetronic sensor or eccentric-shaft motor has been replaced.
Ask for the last two service invoices, because a heavily sooted sensor usually goes hand in hand with long oil intervals.
What it costs to put right
$350 to $1,700 at New Zealand independent workshop rates. That is for this job on its own, not for the car.
Ask the seller
- “Has the car ever gone into limp mode or lost power suddenly?”
- “Has the Valvetronic sensor or eccentric-shaft motor been replaced?”
- “Is there a warning light that comes and goes?”
Now check the BMW 1 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
- Pelican Parts DIY technical article — 'BMW E90 Eccentric Shaft Position Sensor Replacement'
- Fluid MotorUnion technical write-up — 'Fixing a BMW Valvetronic eccentric shaft failure codes'
- BimmerFest thread — 'Another Valvetronic Fault... ECU failure?'
- Motronix technical article — 'BMW Valvetronic Eccentric Shaft Sensor Failure: Oil in Connector Signs'
BMW 1 Series buyer questions
Is n45/n46 valvetronic eccentric shaft sensor and motor failure (e87 116i/118i/120i) serious on a BMW 1 Series?
We rate it major and common on the BMW 1 Series. The N45 and N46 four-cylinders meter airflow with Valvetronic — an electric motor turning an eccentric shaft to vary how far the inlet valves open — and a single position sensor reads that shaft. Oil and combustion soot creep down the sensor's connector and coat its face, the engine management loses confidence in the valve-lift signal, and the car drops into a limp mode with almost no power. There is no second sensor to fall back on, so one dirty sensor is enough to strand the car. Sometimes it is only the sensor and its O-ring; on higher-mileage cars the eccentric-shaft motor is worn or the shaft is binding, which is a far bigger bill.
How much does it cost to fix on a BMW 1 Series?
$350 to $1,700 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 1 Series years are affected?
Our research records this fault on the 2004–2011 BMW 1 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?
Start the engine from cold and let it idle, because the fault most often shows in the first minute — a car already warmed up before you arrive deserves a second visit at a time you choose. Watch the engine warning light through the whole test drive, and specifically after a hot restart: stop, switch off, wait a minute and start it again. Listen for a hesitant, drawn-out crank rather than an instant catch. Ask the seller whether the car has ever gone into limp mode, and whether the Valvetronic sensor or eccentric-shaft motor has been replaced. Ask for the last two service invoices, because a heavily sooted sensor usually goes hand in hand with long oil intervals. Look here: Top of the cylinder head under the plastic engine cover — the sensor screws into the head at the front, with the eccentric-shaft motor mounted alongside it.