Fault Tracing
GeneralIn event of charging problems where no direct fault symptoms are evident it is advisable to check the complete circuit as described in this section.
However, if you only want to check the voltage, start from:
- B6 Measurement of unloaded charging voltage.
- B7 Measurement of charging voltage under load.
Symptoms and causes
1 Battery partly or completely discharged
- fan belt, loose
- current loss
- defective battery
- faulty diodes or dirty slip ring
- faulty voltage regulator
- cables between battery - alternator or between battery - ground, damaged or loose (voltage drop)
- too many electrical circuits connected
2 Warning lamp does not glow with ignition turned on
- fuse blown - check
- bulb blown - check
- worn brushes
- break in armature circuit
- faulty voltage regulator
- damaged or loose cables
3 Warning lamp glows after ignition switch has been turned off and engine has stopped
- shorted positive power diode in alternator (heavy drain on battery - disconnect to avoid complete discharge)
4 Warning lamp glows brightly at high engine speeds
- defective fan belt
- faulty voltage regulator
- faulty diodes or dirty slip rings
- short circuited armature coil or "DF-lead" to ground
- short circuited D+/61 lead to ground
5 Warning lamp glows brightly with ignition turned on and engine not running, but glows or flashes with engine running
- fan belt loose
- faulty voltage regulator
- loose cables causing voltage drop
- break in alternator diode circuit
B1 Checking fan belt tension
Belt is set correctly when it can be depressed 5 - 10 mm (0.2 - 0.4 in). A damaged or worn belt must be replaced.
B2 Checking current loss
WARNING! Wear safety glasses when checking battery. If battery is dirty it should be cleaned with luke warm water and dried properly to avoid surface discharge.
There should be no current drain when ignition is switched off. Current consumption of clock is negligeable. It draws approx. 5 mA which can be compared to a test lamp that requires 230 mA.
Test method:
- switch off ignition and all electrical circuits
- disconnect battery ground lead and connect a test lamp between battery pole and lead, test lamp should not glow. If it does, it indicates a current loss. (Currents less than 100 mA can only be measured with a millimeter.)
B3 Checking specific gravity
Measure specific gravity of all cells:
Condition of battery Specific gravity Voltage
Fully charged 1.28 12.7
Half-discharged 1.21 12.3
Discharged 1.13 11.6
B4 Charging battery
Charge battery for approx. 10 hours at 5 - 6 A. Measure specific gravity of all cells. Specific gravity of a fully charged battery is 1.28 (20 °C = 68 °F). Difference between highest and lowest values measured must not exceed 0.03
B5 Testing battery 1*
WARNING! Wear safety glasses when checking specific gravity.
NOTE: Specific gravity of battery musts be at least 1.21 (see B3). 1* A battery tester can also be used.
- disconnect battery negative lead (lead 1) from ignition coil
- crank starter motor for 10 sec. and check voltage. Voltage must not be less than 9.5 V
- check if air bubbles appear in electrolyte when starter motor is operated.
B6 Measuring unloaded charging voltage
NOTE: Specific gravity of electrolyte must be at least 1.21 (see B3).
- connect a voltmeter across battery poles
- run engine at 33.3 r/s (2000 rpm)
- with exception of day running lights, no other electrical consumers should be connected.
Voltage should be 13.5 - 14.5 V (20 °C = 68 °F)
B7 Measuring charging voltage under load
NOTE: Specific gravity of battery must be at least 1.21 (see B3).
- voltmeter should still be connected across battery poles
- run engine at 33.3 r/s (2000 rpm)
- load alternator according to B10.
Max. voltage drop:
Measure voltage and compare with previous reading. Max. voltage drop = 0.4 V.
Checking voltage drop:
B8 Positive circuit
- connect a voltmeter (range 0 - 4 V) across alternator B+ and battery positive pole
- run engine at 33.3 r/s (2000 rpm)
- load alternator according to B10.
Negative circuit
- connect voltmeter (range 0 - 4 V) across alternator ground and battery (-)
- run engine at 33.3 r/s (2000 rpm)
- load alternator according to B10.
B9 Eliminating voltage drop
Check all connections
- if necessary scrape and clean battery terminals
- check - tighten all connectors
- check ground lead between battery, engine and body
- check B+ starter motor terminals and alternator.
B10
Example
Alternator loading
Engine Alternator rating Consumer connected Load (A)
Carb. 30A Engine 2
35A Low beam+
parking
lights 12
Heated rear
window + 12
--------------
= 26A
Injection 55A Engine 12
Low beam+
parking
lights 12
Heated rear
window + 12
-------------
= 36A
Injection 70A Engine 12
Low beam+
parking
lights 12
Heated rear
window 12
Fan pos.
3 (CU=2) + 9
---------------
= 45A
B11, Loading alternator with adjustable resistor
To prevent voltage drop when testing alternator always use proper connectors or a probe ammeter when connecting ammeter.
B12 Separating alternator faults from voltage regulator faults
Bridge Wire Between D+ and DF:
- disconnect connector from regulator and connect a bridge wire between D+ and DF (red/green wire and brown/white wire)
- connect voltmeter between alternator B+ and alternator ground
- load alternator according to B10
- run engine at 33.3 r/s (2000 rpm).
B13 Checking regulator harness (non-sealed type)
Non-Sealed Connector:
If there are connectors at both ends of wiring harness, remove from car and check for continuity with an ohmmeter or buzzer.
B14 Checking regulator wiring harness (sealed type)
- disconnect connector from regulator. Connect an ohmmeter and check that D+ is connected to alternator ground
- run engine at 25 r/s (1 500 rpm)
- check armature resistance between DF and D-. Correct resistance = 4 ohm (may be 4 - 10 ohm depending on condition of brushes).
B15 Testing alternator-mounted voltage regulator
Three possible fault symptoms are dealt with in this section:
A. Drained battery, alternator does not charge.
B. Poorly charged battery, alternator does not supply sufficient voltage.
C. Battery boils, too high a voltage in charging circuit.
A. Battery charge lamp
Check if lamp lights when engine is operating.
Lamp lights - connect D+ and B+:
Lamp lights: Check fan belts for slipping etc. Connect a bridge wire between alternator D+ and B+ when engine is running.
If lamp still lights, check for open circuit in lead between regulator (short, red) cable and alternator B+. (Current is supplied to regulator along this cable.) Replace if defective. If cable is OK, then either regulator or alternator is defective. Replace regulator and recheck. If fault remains replace alternator.
Lamp does not light
Check bulb. Replace if blown.
Check brushes in regulator
Disassemble regulator.
Check brushes. Replace regulator if brushes are worn (less than 5 mm = 0.2 in above holder).
Check alternator coil for open circuit. Connect ohmmeter to slip rings. If resistance is more than 10 ohm (indicating an open circuit), replace alternator and check regulator. Otherwise replace regulator.
B16 B. Checking voltage (low)
Measure voltage at gray B+ alternator cable, at min. 2500 rpm.
If voltage is greater than specified the battery may be poorly charged and/or there may be too many current consumers connected to circuit. If voltage is less than specified there may be a voltage drop along cable connected between battery and alternator.
Checking voltage drop on (-) side, measure voltage across battery poles. Then measure voltage between battery (+) and alternator ground (casing). It is also possible to measure voltage between alternator housing and body, and between body and battery (-). Replace cable or alternator as required.
Transistor voltage regulator: Check continuity of red cable between regulator and battery (+). If circuit is open, voltage is incorrectly regulated via alternator (B+). Replace cable or alternator as required.
B17 C. Checking voltage (high)
With engine running, measure voltage across battery poles. Install new regulator if voltage is more than 15 V. Also check (at room temperature) that alternator field coil is OK.
Measure resistance across slip rings. If less than specified, replace alternator.
If regulator voltage is less than 15 V: check voltage in relation to temperature/voltage specifications. Replace battery if voltage is not to specification. Transistorized regulator: Check cable to temperature sensor, replace if damaged.
Wiring diagram
Transistorized voltage regulator
A Battery
B Temperature sensor
C Regulator
D Alternator
E Fuse
F Ignition switch
G Battery charge lamp
Customer interview
If no faults can be established in the charging system, ask the customer to describe his driving mannerisms and how he uses the car's electrical equipment. If the car is used often for short trips and power consumption is high, occasional recharging of the battery will be necessary