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BMW N46 B20 / N46 B18 Engine Workshop Manual & Wiring Diagram, detailed repair and maintenance guide for the BMW N46B20 / N46B18 . Includes specifications, step-by-step repair instructions, and electrical diagrams for diagnostics and maintenance. The manual will be useful to owners, auto mechanics, and repair specialists for accurate restoration of engine performance and maintenance of engine reliability.
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The main problem areas of N46:
Valvetronic system
Worn eccentric shaft and Valvetronic sensor.
Symptoms: unstable speed, system errors, loss of traction.
Timing chain
Stretched chain and worn tensioner are common, especially after 120-150 thousand km.
Symptoms: metallic noise when starting, valve timing errors.
Oil consumption (increased oil consumption)
Reason: coking of oil scraper caps, wear of piston rings.
The problem can appear already by 100-120 thousand km.
Ignition coils and spark plugs
Bosch/Delphi coils often fail, causing triple and errors in cylinders.
Cooling system
Plastic elements (thermostat housing, pipes) are prone to cracking.
Overheating is possible if not replaced in a timely manner.
Crankcase ventilation (CVV)
The membrane in the ventilation valve breaks over time, which increases oil consumption and causes mixture errors.
Sensors
The camshaft, crankshaft, and mass air flow (MAF) sensors often fail.
BMW N46B20 Common Fault Codes and Causes
P0171 / P0174 – System Too Lean (Bank 1 / Bank 2)
Cause: Vacuum leaks, dirty MAF sensor, faulty intake boot, or weak fuel pump/injectors.
P0300 / P0301–P0304 – Random or Cylinder-Specific Misfire
Cause: Worn spark plugs, ignition coils failure (very common), or valve cover gasket oil leakage.
P0011 / P0012 – “A” Camshaft Position Timing Over-Advanced / Retarded (Bank 1)
Cause: Faulty VANOS solenoids, dirty oil, incorrect oil pressure, or timing chain stretch.
P0365 / P0369 – Camshaft Position Sensor “B” Circuit (Bank 1)
Cause: Defective camshaft position sensor (exhaust side) or wiring damage.
P0420 / P0430 – Catalyst System Efficiency Below Threshold (Bank 1 / 2)
Cause: Clogged or worn catalytic converter, lambda (O2) sensor malfunction, or exhaust leaks.
P0440 / P0442 / P0455 – EVAP System Leak Detected
Cause: Loose or cracked fuel cap, leaking purge valve, or damaged EVAP hoses.
P0115 / P0118 – Engine Coolant Temperature Sensor Circuit Malfunction
Cause: Bad coolant temperature sensor or wiring issue.
P0100 / P0102 – Mass Air Flow (MAF) Circuit Malfunction / Low Input
Cause: Dirty or faulty MAF sensor, intake air leaks, or disconnected sensor plug.
P0505 – Idle Control System Malfunction
Cause: Dirty throttle body, faulty idle air control valve (IAC), or intake leaks.
P1520 / P1523 – Variable Camshaft Timing (VANOS) Malfunction
Cause: VANOS solenoid failure, oil sludge buildup, or timing chain tensioner problems.
P1111 / P1112 – VANOS Inlet / Exhaust Control Faults
Cause: Incorrect camshaft adjustment due to clogged solenoids or bad oil flow.