BMW Cars 1999-06

Cables & Clamps


Once a year (or as necessary), the battery terminals and the cable clamps should be cleaned. Loosen the clamps and remove the cables, negative cable first. On batteries with posts on top, the use of a puller specially made for this purpose is recommended. These are inexpensive and available in most auto parts stores. Side terminal battery cables are secured with a small bolt.

Clean the cable clamps and the battery terminal with a wire brush, until all corrosion, grease, etc., is removed and the metal is shiny. It is especially important to clean the inside of the clamp thoroughly (an old knife is useful here), since a small deposit of foreign material or oxidation there will prevent a sound electrical connection and inhibit either starting or charging. Special tools are available for cleaning these parts, one type for conventional top post batteries and another type for side terminal batteries. It is also a good idea to apply some dielectric grease to the terminal, as this will aid in the prevention of corrosion.

After the clamps and terminals are clean, reinstall the cables, negative cable last; DO NOT hammer the clamps onto battery posts. Tighten the clamps securely, but do not distort them. Give the clamps and terminals a thin external coating of grease after installation, to retard corrosion.

Check the cables at the same time that the terminals are cleaned. If the cable insulation is cracked or broken, or if the ends are frayed, the cable should be replaced with a new cable of the same length and gauge.

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Fig. Maintenance is performed with household items and with special tools like this post cleaner

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Fig. The underside of this special battery tool has a wire brush to clean post terminals

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Fig. Place the tool over the battery posts and twist to clean until the metal is shiny

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Fig. A special tool is available to pull the clamp from the post

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Fig. The cable ends should be cleaned as well

Disconnecting The Cables

When working on any electrical component on the vehicle, it is always a good idea to disconnect the negative (-) battery cable. This will prevent potential damage to many sensitive electrical components such as the Powertrain Control Module (PCM), radio, alternator, etc.

Never disconnect a battery cable when the engine is running. Disconnecting a battery cable with the engine running is likely to cause expensive and permanent damage to the alternator, voltage regulator, and control modules, such as the PCM.

Any time you disconnect or remove the battery cables, it is recommended that you disconnect the negative (-) battery cable first. This will prevent your accidentally grounding the positive (+) terminal to the body of the vehicle when disconnecting it, thereby preventing damage to the above mentioned components.

Before you disconnect the cable(s), first turn the ignition to the OFF position. This will prevent a draw on the battery which could cause arcing (electricity trying to ground itself to the body of a vehicle, just like a spark plug jumping the gap) and, of course, damaging some components such as the alternator diodes.

When reconnecting or installing a battery, always attach the negative cable last. This is done as a safety measure, should a tool or component slip while installing the positive battery cable. If the tool touches the battery positive terminal and a chassis ground simultaneously, as long as the negative battery cable is not connected, no damage will occur. Make sure when installing a battery that the positive battery cable is fully installed and tightened before installing the negative battery cable.

When the battery cable(s) are reconnected (negative cable last), be sure to check that your lights, windshield wipers and other electrically operated safety components are all working correctly. If your vehicle contains an Electronically Tuned Radio (ETR), don't forget to reset your radio security code, the radio station presets, and reset the clock.

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Fig. The battery is neatly tucked into the right rear trunk well underneath a plastic tray on E36 3 Series vehicles

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Fig. The positive battery cable is rather lengthy on all E36 models. The cable is connected to the battery in the trunk and is routed to the jump post on the right front of the engine compartment

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Fig. The top and the front cover can be removed from the E36 positive jump post box to check the positive battery cable connection. The negative battery cable must be disconnected before attempting this

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Fig. The jump post block on E36 models serves as a junction for five cables. The large cable from the battery's positive terminal is the one on the lower left