How to Diagnose Why Your Late-model BMW is Stalling

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If you have a late model vehicle with a stalling issue, there are many things that can make it happen. The good news is that the check engine light should be illuminated on your dash, and that will make it simpler to diagnose.

If you have a vehicle that is a model year 1996 or newer, your vehicle is equipped with an OBDII system. This simply put is an on board diagnostic system, if the computer on your vehicle detects a fault, it will set a code and turn on your check engine light. Many different things can cause the check engine light to come on, from an engine misfire to a transmission slip, a good rule to remember, though, is that if the light is illuminated your vehicle is putting out more emissions than it was designed to. With OBDII cars, any generic computer diagnostic tool can communicate with the vehicle PCM (computer) and tell you what the fault code is, that fault code will tell you where the computer believes the fault is.

It is possible to go somewhere like Advance Auto Parts to have the code pulled from the computer for free. There are two things you need to remember, though. First, do not let them turn the light off. Chances are the light will come on again within 50 miles, and if it's an intermittent problem you have just erased the diagnostic information a repair technician needs to fix it. Second, it is possible to get a code, for example, for a bad oxygen sensor, but have a secondary issue that is causing that fault. In other words, you are almost always better off taking your vehicle to a qualified technician to have it diagnosed. You don't have to take it back to the dealership, you can take it to an independent shop that handles computerized diagnostics.

The 2001 BMW 3 series did have a problem with stalling, many times it was because of a problem with the camshaft sensor. However, it could also be related to a vacuum leak, an intake air leak or a crankcase ventilation fault.

If the check engine light is not on and you are having a stalling problem, it is highly possible that the throttle plates are carboned up and need cleaned. Another possibility is that there is an idle air control valve that is sticking. If the problem is happening more in the cold weather, it probably is a problem with carbon buildup. If you remove the air duct and see a lot of black buildup, that's what is causing the problem. Most garages should be able to clean that for you, I would also consider having the top end cleaned and possible a tune up. A healthy running engine can overcome a carbon buildup problem, but if the engine is already compensating for a problem spark plug, for example, it will lead to stalling.

If the check engine light is not on and carbon is not the problem, you should plan on leaving the vehicle with a garage for a couple days because they may have to drive the vehicle until it acts up before they can diagnose the problem. With this sort of problem, it's impossible to know exactly what is happening until the fault occurs while connected to diagnostic equipment.

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Posted on Feb 6, 2011