Over the few years I have owned my car (BMW 318i e46 N42) I have come across a few issues which were down to wear and tear of sensors / consumable parts and also some faults. Below is the list of the problems I faced and how they were resolved. Generally most BMW e46s would show similar symptoms and the solution would most probably be the same too. This article will help you diagnose the fault up to a certain extent and you may also be able to fix the problem yourself by following one of my DIYs.

Note: The remedy for each fault may 'not always' be as below.

Air Conditioning
PROBLEM	FAULT	REPAIR
The Air Conditioning sounds like it is working (the compressor engages), but gives no cool air, even when re-gassed.	The compressor is faulty - Needs replacing + re-gassing. Total OEM solution will cost £850.	OEM part cost £520 BMW part costs £750
The air blower in the car blows high and low (fluctuates) for a few minutes when you start the car.	Final Stage / Heater Blower Resistor - Needs replacing.	OEM part cost £47 BMW part cost £102
Most times the Air Conditioning does not give cool air, however some times it does.	Either the Air Conditioning System needs re-gassing or Check if the Compressor is engaging, if not, then check if the Radiator fan is spinning. If the Radiator fan does not work, then replace the fan, it will fix the Air Conditioning The Air Conditioning System requires re-gassing every 2 / 3 years. It can be done at Kwik Fit, costs £45 and takes 1 hour. Private Air Conditioning companies charge £80.	OEM part costs £138 BMW part costs £280

 

Engine
PROBLEM	FAULT	REPAIR
Engine cuts outs randomly / power loss, every so often and then while driving (and red light goes on) and it is not possible to restart the engine for up to 20 mins, no matter what you do.	Crankshaft Sensor Faulty - Needs replacing.	BMW part costs £68
Every now and then the engine takes up to 40 seconds to start, even if you keep the key fully turned.	Cam Sensor Faulty - Needs replacing.	BMW part costs £68
The engine yellow lights goes on and the car engine knocks / vibrates. You need to take the car up to 4000 revs to be able to change the gear to stop the car knocking. Loss of power, i.e. you only get 75% of the engine power.	One of more of the Ignition Coils are faulty - Needs replacing. When the ignition coils are changed, it is recommended that all Spark Plugs are also changed.	Each Plug from BMW costs £8 Each Ignition Coil from BMW costs £35

Mechanical
PROBLEM	FAULT	REPAIR
You hear a loud crack while rolling up / down your electric window, after which the window may not move any more or only very slowly.	Window Regulator Glider clip has broken - Either DIY repair it, or replace the whole Window Regulator.	Glider Clip is available as a separate part on eBay £5 BMW cost for whole Window Regulator Costs £85
The Radiator Fan turns on automatically while the car engine is already switched off. It remains on until you do something about it.	The Radiator fan is faulty - Needs replacing.	OEM part costs £138 BMW part cost £280
The front of the car vibrates when you brake, while driving fast.	Possibly the Ball Joints have play, and or the Bushes need changing. if ball joints have play, then the entire Wishbone will have to be replaced.	BMW Wishbone costs £120 BMW Bush set costs £85
There is a continuous humming sound when the car is moving.	Either of the 4 wheel bearing needs replacing.	OEM parts costs £76 + 2 hrs labour
The steering wheel gets locked and stuck when turned to the extreme left or right.	The alignment is out by quite a bit.	Alignment costs £30

Electrical
PROBLEM	FAULT	REPAIR
A bulb warning light indication keeps coming on, even though the front or back light bulbs are ok.	A particular bulb socket and contact is faulty - replace them and also the housing.	BMW Parts cost £35 BMW total cost £155
CD Changer doesn't work, or isn't recognised by the Radio.	Try pulling out and re-inserting the 3 fuses for the Radio. This some times resets the CD Changer.	Free
CD changer magazine cartridge is stuck / cd is stuck in changer / display says No Magazine Found.	You can open it up, release the stuck CD and it will start working again, but it will only last a few days before jamming again. You need a new CD Changer, or convert the cable connector to use another compatible / brand CD changer.	BMW sell the CD Changer for £700. eBay have 2nd hand ones, but how long before they will also fail?
Air Bag light goes on intermittently, may be only when the passenger is in the car.	The occupancy sensor matt for passenger recognition is faulty - Needs replacing.	BMW part cost £80 BMW total cost £307