Learn how to diagnose & repair BMW Electrical problems:
BMPdesign will help you recognize BMW electrical problems & issues before it is too late. The following BMW electrical repair technical advice, recommendations, tech tips, and videos will teach you how to diagnose, and repair your BMW's damaged or worn electrical components.
With over 30 years experience, our BMW repair videos and instructions will give you helpful tips on weaknesses that your specific model may have. Knowing this information in the beginning will save you hundreds of dollars by aiming you in the right direction before you purchase unnecessary parts. Send us a repair request!
A quick overview, the major components, and some troubleshooting tips of your BMW's electrical system are explained below.
The battery is an electrical storage device (12 volts) used to start the engine and help operate the electrical accessories installed on your BMW. The battery consists of six cells. Each of the six cells "stores" 2.1 volts for a total of 12.6 volts.
(WARNING: The chemical reaction creates dangerous, explosive gases that vent through the battery cover vents. Care should always be taken when charging or jump starting low batteries and whenever working under the hood of the car. Always keep the battery clean to allow proper ventilation. Some batteries use a gel to replace the electrolyte for a somewhat safer battery and the use of "maintenance-free" batteries has eliminated the need for refilling the electrolyte. However, all batteries lose charging capacity over time through the loss of the electrolyte, deterioration of the plates and chemical breakdown of the connections.)
Charging or starting system failure:
1. Before replacing any battery due to a failure, have the battery and the car's electrical system tested for proper functioning. (a weak alternator charging system will damage and drain a new battery)
2. The most basic test that should be performed first is a visual and voltage test of the battery. Knowing the exact condition of the battery is the best way to know whether or not to suspect other system components.
3. To analyze the condition of a battery, use a Digital Volt Ohm Meter to check the amount of charge, and a battery charger to create an external charge. (Be sure to follow your chargers instructions, and select the lowest amp charge for better results.)
4. An average battery should last 3-5 years in average climates but those in high heat or extreme cold areas may last only 2-3 years. The replacement battery should always have the same or higher CCA rating (cold cranking amps) as the original and be of the same or compatible "group size" to fit the battery tray and cable connections.
The BMW alternator produces electricity used to maintain battery storage charge and to help run all the electrical accessories.
Most alternators now use internal voltage regulators to maintain the proper system voltage, from 12.6-14.5 volts.
A BMW alternator does not constantly produce electricity. It cycles on and off as demand goes up and down.
As the demands from electrical devices are placed on the alternator and battery, the average BMW alternator may only last 3-4 years, causing a dead battery prematurely.
Typical Charging System Power Demands:
Equipment Electrical Draw
Rear Window Defogger 25 amps
High Blower 20 amps
Headlamps (low) 15 amps
Windshield Wipers 6 amps
Ignition 6 amps
Brake Lights 5 amps
Total 77 Amps
This doesn't include amperage requirements for items like cell phones, laptops, CD players, or additional lights.
Having an operational warning light for the alternator is crucial to catching problems.
This signal light is linked directly to the alternator through its terminal.
Check the warning light circuit by turning on the ignition without cranking the engine; If the light comes on briefly, the alternator and wiring are okay, but if the light does not come on, the alternator and wiring should be checked. (Don't forget to check the fuse that controls the light circuit also.) Checking out these simple circuits first can greatly reduce your troubleshooting time and unnecessary replacement of your alternator.
As the car idles for extended periods of time during high heat conditions, a number of things happen that contribute to "lowered" alternator output.
Heat created reduces the alternator's charging capacity to reduce the chance of overcharging the battery.
Newer designed alternators have a "delay/soft start" built into the regulator circuit which delays the load being placed upon the engine when starting up.
An alternator may only be able to produce up to 70% of its rated output under adverse conditions.
The starter is the largest power consumer on your vehicle, which is a DC motor that turns the engine crankshaft through the flywheel, starting the combustion process by creating compression within the cylinders. Voltage to the starter is supplied directly from the battery and is controlled by a relay and/or solenoid operated from the key switch inside your BMW.
A slow cranking engine may be a sign of a bad starter and with age, that's more and more likely. But on most cars today, it's due to low battery voltage, poor electrical connections at the battery or a failed relay or fusible link.
Starting your BMW with the major components turned off (like the AC compressor, blower motor and high-powered stereos) will greatly ease the load on the starter. Most new cars have relays that will not allow the AC compressor and alternator to turn on until after the vehicle has been started.
It is best to replace the BMW starter and solenoid as a unit and have the electrical system checked at the same time to prevent further problems.
BMW Troubleshooting & Maintenance Tips
Your BMW's electrical system should be completely checked and tested every two years or whenever serviced for any type of driveability problem.
Many problems associated with day-to-day driving are caused by voltage variations and must be the first step in troubleshooting any problem.
Your BMW's electrical system must be load tested to certain standards. Electrical systems operating at 80%-100% of capacity are needed. It is crucial that it be up to standards.
If voltmeter testing doesn't pinpoint the problem, get a thorough checkup done from an auto electrical technician who knows your BMW's system. Most major chain auto parts stores offer a free service test good enough to notify you of any major problems.
Most early problems start from poor electrical connections due to loose connections and/or buildup of corrosion, especially at the battery posts. Keep that battery clean!
Parts you should consider when working on BMW electrical problems:
Battery BMW Alternator BMW Starter Battery Cables & Connectors DVOM (digital volt-ohmmeter) Ammeter (for testing circuit load) Battery post cleaner brush or tool Battery charger (w/overcharge protection) Spare fuses of all sizes in car Repair manual with electrical schematic
BMP Design Repair Tech Tips are added regularly. Come back often to check for new BMW Repair topics. These repair tips are designed only as a starting point. Please seek the assistance of a professional BMW mechanic for all repair problems beyond your capabilities.
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