Mitsubishi Grandis. Manual - part 646

CHARGING SYSTEM

ENGINE ELECTRICAL

16-8

REGULATED VOLTAGE TEST

M1161001100473

This test determines whether the voltage regulator 
correctly controlling the alternator output voltage.
1. Always be sure to check the following before the 

test.

• Alternator installation

• Check that the battery installed in the vehicle is 

fully charged.

(Refer to 

P.54A-6

, GROUP 54A 

− Battery − 

On-Vehicle Service.)

• Drive belt tension

(Refer to 

P.11A-7

, GROUP 11A 

− On-Vehicle 

Service.)

• Fusible link

• Abnormal noise from the alternator while the 

engine is running

2. Turn the ignition switch to the "LOCK" (OFF) 

position.

3. Disconnect the negative battery cable.
4. Use the special tool Alternator test harness 

(MB991519) to connect a digital voltmeter 
between the alternator "S" terminal and earth 
[Connect the (+) lead of the voltmeter to the "S" 
terminal, and then connect the (-) lead of the 
voltmeter to a secure earth or to the battery (-) 
terminal].

5. Connect a clamp-type DC test ammeter with a 

range of 0 

− 150 A to the alternator "B" terminal 

output wire.
NOTE: The way of disconnecting the alternator 
output wire and of connecting the ammeter is 
possibly not found the problem that the output 
current is dropping due to the insufficient 
connection between terminal "B" and the output 
wire.

6. Reconnect the negative battery cable.
7. Connect the MUT-III (to show the engine speed).
8. Turn the ignition switch to the "ON" position and 

check that the reading on the voltmeter is equal to 
the battery voltage.
NOTE: If the voltage is 0 V, the cause is probably 
an open circuit in the wire or fusible link between 
the alternator "S" terminal and the battery (+) 
terminal.

9. Turn all lamps and accessories off.
10.Start the engine.
11.Increase the engine speed to 2,500 r/min.
12.Read the value displayed on the voltmeter when 

the alternator output current alternator becomes 
10 A or less.

AK304844 AB

Battery

Ignition
switch-IG

Engine-ECU
<M/T> or
Engine-A/T-
ECU <A/T>

Ammeter (clamp-type)

Load

Black

MB991519

Voltmeter (digital-type)

Red

Yellow

Blue

Alternator

B

FR

L

S

G

Charging 
warning lamp

Combination meter

+

-

+

-

CHARGING SYSTEM

ENGINE ELECTRICAL

16-9

13.If the voltage reading conforms to the value in the 

voltage regulation, then the voltage regulator is 
operating normally.
If the voltage is not within the standard value, 
there is a malfunction of the voltage regulator or of 
the alternator.

14.After the test, lower the engine speed to the idle 

speed.

15.Turn the ignition switch to the "LOCK" (OFF) 

position.

16.Remove the MUT-III.
17.Disconnect the negative battery cable.
18.Disconnect the ammeter and voltmeter.
19.Connect the alternator output wire to the 

alternator "B" terminal.

20.Remove the special tool, and return the connector 

to the original condition.

21.Connect the negative battery cable.

Voltage Regulation Table

Standard value:

WAVEFORM CHECK USING AN OSCILLOSCOPE

M1161001200179

MEASUREMENT METHOD

Connect the oscilloscope special patterns pick-up to 
the alternator "B" terminal.

STANDARD WAVEFORM

Observation Conditions

Inspection terminal

Voltage regulator ambient 
temperature 

°C

Voltage V

Terminal "S"

−20

14.2 

− 15.4

20

13.9 

− 14.9

60

13.4 

− 14.6

80

13.1 

− 14.5

AK100002

Alternator

"B" terminal

CH1

AC

Function

Special pattern

Pattern height

Variable

Variable knob

Adjust while viewing the waveform.

Pattern selector

Raster

Engine speed

Curb idle speed

CHARGING SYSTEM

ENGINE ELECTRICAL

16-10

NOTE: 

The voltage waveform of the alternator "B" terminal 
can undulate as shown in the illustration. This 
waveform is produced when the regulator operates 
according to fluctuations in the alternator load 
(current), and is normal for the alternator. In addition, 

when the voltage waveform reaches an excessively 
high value (approximately 2 V or higher at idle), it 
often indicates an open circuit due to a brown fuse 
between alternator "B" terminal and battery, but not a 
defective alternator.

EXAMPLE OF ABNORMAL WAVEFORMS

NOTE: 

.

1. The size of the waveform patterns differs largely, depending on the adjustment of the variable knob on the 

oscilloscope.

2. Identification of abnormal waveforms is easier when there is a large output current (regulator is not 

operating). (Waveforms can be observed when the headlamps are illuminated.)

3. Check the conditions of the charging warning lamp (illuminated/not illuminated). Also, check the charging 

system totally.

AKX00189

0.4

(V)

0.2

  0

–0.2

–0.4

Voltage at
alternator
"B" terminal

Time

AG

AKX00190

CHARGING SYSTEM

ENGINE ELECTRICAL

16-11

Abnormal waveform

Problem cause

Example 1 

Open diode

Example 2 

Short in diode

Example 3 

Broken wire in 
stator coil

Example 4 

Short in stator 
coil

AKX00191

AKX00192

AKX00193

AKX00194