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Test battery/alternator
The following table provides an overview of the alternator check
procedure.
Battery check
1.) Measure off-load voltage
- Voltage measurement at battery terminal 30 and battery terminal
31.
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Off-load voltage, reference value:
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12,8 - 13,2 V
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Reference value not attained:
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Charge or replace battery
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2.) Battery Test:
- Test battery with tester KM-J-42000
Alternator check
3.) Visual testing:
- Connect battery to supply system
- Ensure V-belt tension complies with auto manufacturer data
4.) Measure no-load control voltage
- Start cold engine (no consumers)
- Engine speed 2000 rpm
- Measure control voltage at alternator connection B+ and
alternator housing (not at battery terminals)
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Control voltage, reference value:
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13,7 - 14,8 V
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Reference value not attained:
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Vehicle with petrol engine: continue with test step 5
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Vehicle with diesel engine: continue with test step 7
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Reference value attained:
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continue with test step 9
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5.) Test preexciting circuit:
- Remove terminal L wiring harness plug
- Voltage measurement at terminal L and battery terminal 31
- Ignition ON
- Engine OFF
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Voltage, reference value:
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less than 5 V
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Reference value not attained:
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- test wiring harness between alternator terminal L and engine
control unit for short-circuit against voltage, earth and break
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or
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- replace engine control unit
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Important:
Components must be replaced in the specified sequence.
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Reference value attained:
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continue with test step 6
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6.) Preexciting circuit:
- Connect terminal L wiring harness plug
- Voltage measurement (with adapter cable) at terminal L and
battery terminal 31
- Engine RUNNING
- switch on consumer (lights, heated rear window, heater fan,
etc.)
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Voltage, reference value:
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greater than 5 V
(depending on engine speed and output of the
connected consumer)
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Reference value not attained:
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- test wiring harness between alternator terminal L and engine
control unit for short-circuit break
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or
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- replace engine control unit
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Important:
Components must be replaced in the specified sequence.
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Reference value attained:
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- replace alternator control unit (if control unit is listed
separately according to EPC)
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or
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- Replace alternator
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Important:
Components must be replaced in the specified sequence.
7.) Test preexciting circuit:
- Remove terminal L, F wiring harness plug
- Voltage measurement at terminal L, F and battery terminal
31
- Ignition ON
- Engine OFF
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Voltage reference value, terminal L:
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greater than 8 V
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Voltage reference value, terminal F:
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less than 5 V
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Reference value not attained:
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test wiring harness between alternator terminal L, F and engine
control unit for short-circuit against voltage, earth and break
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or
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- engine control unit
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Important:
Components must be replaced in the specified sequence.
8.) Test preexciting circuit:
- Connect terminal L, F wiring harness plug
- Voltage measurement (with adapter cable) at terminal L, F and
battery terminal 31
- Engine RUNNING
- switch on consumer (lights, heated rear window, heater fan,
etc.)
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Voltage reference value, terminal L:
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greater than 5 V
(depending on engine speed and output of the
connected consumer)
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Voltage reference value, terminal F:
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greater than 5 V
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Reference value not attained:
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- test wiring harness between alternator terminal L, F and
engine control unit for break
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or
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- replace engine control unit
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Important:
Components must be replaced in the specified sequence.
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Reference value attained:
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- replace alternator control unit (if control unit is listed
separately according to EPC)
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or
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- Replace alternator
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Important:
Components must be replaced in the specified sequence.
9.) Alternator charge testing:
- Position clamp-on ammeter as close to alternator B+ connection
as possible
- Measure control voltage at battery terminal 30 and battery
terminal 31
- Start engine
- Engine speed approx. 2000 rpm
- Charge the supply system (battery) with 50 % of the current
strength specified on the rating plate.
Example: for an 80 amp (A) alternator, the following consumers
would be switched on to achieve a charge of 40 A:
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Lights:
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approx. 12 A
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Heated rear window:
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approx. 10 A
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Fog lights:
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approx. 8 A
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Interior fan:
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approx. 8 A
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Air-conditioning unit:
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approx. 8 A
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Total:
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approx. 46 A
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- Here, the control voltage must not fall more than 0.5 V below
the reference value.
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Control voltage, reference value:
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13,7 - 14,8 V
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Reference value not attained:
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continue with test step 10
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Reference value attained:
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see instruction for static current measurement
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10.) Charge test 1, charging current circuit:
- Connect bridge cable between battery terminal 31 and alternator
housing:
- Control voltage at battery terminal 30 and battery terminal
31
- Here, the control voltage must not fall more than 0.5 V below
the reference value.
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Control voltage, reference value:
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13,7 - 14,8 V
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Reference value not attained:
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continue with test step 11
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Reference value attained:
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High contact resistance between battery terminal 31 and
alternator housing
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11.) Charge test 2, charging current circuit
- Connect bridge cable between battery terminal 30 and B+:
- Measure control voltage at battery terminal 30 and battery
terminal 31
- Here, the control voltage must not fall more than 0.5 V below
the reference value.
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Control voltage, reference value:
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13,7 - 14,8 V
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Reference value not attained:
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Replace alternator
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Reference value attained:
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High contact resistance between battery terminal 31 and
alternator housing
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Oscilloscope - reference images:
- Test alternator with oscilloscope (connect as for voltage
measurement to B+ and alternator housing)
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Alternator without error
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Alternator with phase error
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Alternator with diode error (plus or minus diode break)
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Alternator with diode error, plus or minus diode (short-circuit
- alternator excited)
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Alternator with diode error, plus or minus diode (short-circuit
- alternator not excited)
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Instruction for static current measurement:
Unpermissibly high battery discharge may also
result from drawing of an increased static current.
- Drawing of the static current is dependent on:
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- vehicle equipment
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- control unit tracking time
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