BMW 3 Series Service Manual (E39)

Battery, Starter, ~iternatorl

The battery is mounted in the right side of the luggage compartment, concealed behind a trim panel. Battery capacity is determined by the amount of current needed to start the vehicle and by the amount of current consumed by the electrical system. This will vary from model to model.

BMW batteries are rated by amperelhours (Ah) and cold cranking amps (CCA) rating, which are listed on the battery. The Ah rating is determined by the average amount of current the battery can deliver over time without dropping below a specified voltage. The CCA is determined by the battery's ability to deliver starting current at On F (-18" C) without dropping below a specified voltage. Always replace the battery with one having the same or higher ratings.

Battery testing

Battery testing determines the state of battery charge. On conventional or low-maintenance batteries. the most common method of testing the battery is that ofchecking the specific gravity of the electrolyte using a hydrometer. Before

testing the battery, check that the cables are tight and free of

-

corrosion.

Hydrometer testing

Before hydrometertesting, load the battery with 15 amperes for one minute. If the battery is installed in the vehicle, this can be done by turning on the headlights without the engine running. The state of battery charge based on specific gravity values are given in Table b. Specific gravity of battery electrolyte at 27" C (80°F).

The hydrometer indicates the specific gravity of the electrolyte. The more dense the concentration of sulfuric acid in the electrolyte, the higher the state of charge

NOTE-

Electrolyte temperature affects hydrometer reading. Checlc the electrolyte temperature with a thermometer. Add0.004 to the hydrometerreading forevery 6°C (10°F) that the electrolyte is above 27°C (80°F). Subtract 0.004 from the reading forevery 6°C (10°F) that the electrolyte is below27"C

(80°F).

.

Battery, Starter, Alternator

Table b. Specific gravity of battery electrolyte at 27°C (80°F)

if the specific gravity is at orabove 1.225, butthe battery lacks Dower for startinq, determine the battew'sservice condition with a load volta& test. if the average specific gravity of the six cells is below 1.225, remove the battery from the luggage compartment and recharge.

Battery open-circuit voltage test

Before testing, load battery with 15 amperes for one minute with battery load-tester or turn on headlights for about one minute without engine running. Connect digital voltmeter across battery terminals. Open-circuit voltage levels are given in Table c. Open-circuit voltage and battery charge.

If open-circuit voltage is OK but battery still lacks power for starting, perform a load voltage test.

If open-circuit voltage is below 12.4 volts, recharge battery and retest.

Table c. Open-circuit voltage and battery charge

Battery load voltage test

A battery load tester is required for a load voltage test. The test is made by applying a high resistive load to the battery terminals and then measuring battery voltage. The battery should be fully charged forthe most accurate results. The battery cables must be disconnected before malting the test. Replace the battery if the voltage is below that listed in Table d. Battery load test -minimum voltage.

Battery, Starter, ~lternatorl

WARNING-

Always wear protective goggles and clothing when performing a loadtest.

* Measure after applyinga 200 amp load for 15 seconds.

Closed-circuit current measurement

If the vehicle battery is discharged for an unknown reason, perform a closed-circuit current measurement as the first test. For diagnostic purposes, it is important to not disconnect the battery. Disconnecting the battery may reset a faulty control unit, preventing proper diagnosis.

The following test is generally completed overnight using a multimeterwith a closed circuitcurrent measurement adaptor with a recording function

-Check that battery voltage is 12 volts or higher. If lower, recharge battery.

-Switch off electrical consumers (interior lights, telephone, aftermarket equipment, or others).

-Open luggage compartment and remove battery trim panel. Use screwdriver to lock latch on trunk lid or hatch, simulating closed luggage compartment. Close other doors.

-Open driver's door,then close it, simulating driver entering vehicle.

-Switch ignition to RUN position for at least five seconds, then turn ignition to OFF position. This simulates driving vehicle.

-Open and close driver'sdoor, simulating driver leaving vehicle.

-Lock car and arm alarm.

-Wait at least 16 minutes for consumer cut-off.

Battery, Starter, Alternator

Water-cooled alternator

The water-cooled alternator, used on 1999 and later M62TU engines, is a sealed unit housed inside the engine block water jacket. It is cooled via the engine cooling system. It is a "brushless" sealed unit that cannot be serviced. Maintaining consistent alternator temperatures increases the life span of the alternator, and elimination of the alternator cooling fan reduces alternator noise significantly.

The M62 TU water-cooled alternator incorporates load start reduction. This function is intended to shorten the duration of engine starting, particularlyat low ambienttemperatures.The current load is limitedto 20 amps during starting in order to reduce alternator braking torque on the engine. Followingthe current limiting phase, full power output is then progressively reached.

Charging system diagnostics requires special test equipment. If the test equipment is not available, charging system fault diagnosis can be performed by an authorized BMW dealer or other qualified repair shop. See Table a. Battery, alternator and starter troubleshooting for general electrical component troubleshooting.

Before checking the alternator, make sure the battery is fully charged and capable of holding a charge. Check that the battery terminals are clean and tight and the alternator drive belt is properly tensioned and not severely worn.

NOTE-

Some model require up to 15 second to reacli full alternator output.

CAU T I O G

If the charge indicatorlight in the instrumentcluster remains on, the charge warning circuit in the instrumentcluster may be faulty. Check that the groundleadis securelyaffachedto the groundingstudon the cylinder head (A). Replacingthe instrumentcluster before repairingthe groundlead willboth damage the instrumentcluster andcause the failure to reoccur.

Battery, Starter, ~lternatorl

Charging system quick-check

Use a digital multimeter to measure voltage across the battery terminals with key off andthen again with engine running. Battery voltage should be about 12.6 volts with key off and between 13.5 and 14.5 volts with engine running.

NOTE-

The regulated voltage (engine running) shouldbe between 13.2 and 14.5,depending on temperature andoperating conditions. If the voltage is higher than 14.8, the voltage regulator or mulitfunction controller is most likely faulty

Check for clean and tight battery cables. Check groundcable running from negative (-) battery terminal to chassis and ground cable running from engine to chassis. Check alternator drive belt condition and tension.

Charging system, checking

CAUTIOI\C

*Do not disconnect the battery while the engine is running. Damage to the alternatorand/or engineelectronicsystems may result.

Only use a digital multimeter when testing charging system components.

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4 Turn ignition key on. Check that battery warning light comes on.

NOTE-

If the warning light does not come on, repair bulb or wiring faults before continuing to checlc the charging system.

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Charge indicator

502820805

4 6-cylinder engines only, remove complete air filter housing:

Loosen intake duct hose clamp (A) at throttle assembly.

Loosen clamp and remove idle control hose from intake duct (B) and disconnect idle speed control valve electrical harness connector.

Disconnect electrical harness connector (C) from mass air flow sensor.

Remove air filter housing mounting screw (D).

Disconnect vent tube (E).

Loosen air intake duct clamp (F).

Carefully lift air filter housing out of engine bay.