Turbo four-cylinder petrol (320i, 528i, X1, X3). Early years had weak chain guides; high-pressure fuel pumps and coils also act up.
Click a code for the full breakdown: symptoms, causes, and whether you can keep driving.
Crankshaft/Camshaft Position Correlation (Bank 1 Sensor A)
The crankshaft and camshaft positions do not match what the ECU expects - the mechanical timing may be off.
Camshaft Position Timing Over-Advanced (Bank 1)
The intake camshaft timing is more advanced than commanded - the variable valve timing system is not responding correctly.
Random/Multiple Cylinder Misfire Detected
The engine control unit detects misfires occurring randomly across multiple cylinders, meaning combustion is failing intermittently in more than one cylinder.
Cylinder 1 Misfire Detected
Combustion is repeatedly failing in cylinder 1. The ECU counts crankshaft speed fluctuations and attributes them to that specific cylinder.
System Too Lean (Bank 1)
The engine is getting too much air or too little fuel on bank 1 - the ECU has hit the limit of its ability to compensate.
Catalyst System Efficiency Below Threshold (Bank 1)
The downstream oxygen sensor shows the catalytic converter on bank 1 is no longer cleaning exhaust gases efficiently.
Fuel Rail/System Pressure Too Low
Measured fuel pressure is below what the ECU commands - the engine may be starved of fuel under load.
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