Car Bugs

Six weeks ago returning from some trip, I landed in Boston and went to the airport garage to find my car. It wouldn’t start. The entire electrical system was dead, and not even the remote key would work. So I had it towed home, jumped it off one of those handy portable battery units, drove it around for 45 minutes to let the alternator charge the battery and switched it off. And tried to switch it back on. Nothing.

So I figured either the alternator or battery was dead. I don’t drive very much, so for weeks the car just sat idle and lifeless behind my house. This weekend I finally got around to having it towed to the dealer to get repaired, and today I picked it up, fully working. The service receipt says:

CUSTOMER STATES VEHICLE HAD TO BE JUMPED AND AFTER DRIVING FOR AWHILE, THE VEHICLE DID NOT START. CUSTOMER ALREADY HAD A BATTERY REPLACE. HE THINKS IT IS THE ALTERNATOR. PERFORMED DIAG AND REPLACED FAULTY BATTERY. TESTED ALTERNATOR, NO PROBLEMS FOUND. FOUND LSZ DRAWING POWER. RECODED LSZ.

So it sounds like I had a bum battery, but that bit about “RECODED LSZ” at the end sounded interesting and so I decided to check it out.

It turns out that LSZ stands for the German equivalent of “Lamp Switching Center” and is one of the several software modules that control the various systems on a BMW. For example, the “ZKE” module controls the locks and power windows. The LSZ seems to control the various indicator lights inside the car, as well as some elements of the air conditioning and heating (which BMW calls the IHKA).

Well, it turns out that there was a bug in the BMW’s lamp control software program that can render your BMW useless. The official BMW service report states that

If two or more [heating or air conditioning] settings are modified during an ignition cycle (e.g. the temperature and blower setting), the result is an increase in closed circuit current of approximately 800 mA. This could cause a discharged battery when vehicle is not used for 2 to 3 days.”

You can read the entire bulletin here. Instructions for accessing the secret/diagnostic functions on the BMW on-board computer are here.