Mitsubishi Montero (2002-2004). Manual - part 499

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9. If due to external noise: In almost all cases, 

prevention on the receiver side is not possible. 
Weak signals especially are susceptible to 
interference.

If there is more noise than on radios in other vehi-
cles, find out the noise condition and the name and 
frequency of the receiving stations from the owner, 
and consult with the radio manufacturer's service 
center.

INSPECTION PROCEDURE 7: Sound mixed with Noise, Only at Night (AM).

The following can be considered as possible causes 
of noise appearing only at night.
1. It is significantly easier to receive long-distance 

signals at night. This means that even stations 
that are received without a problem during the day 
may experience important to remember that the 
weaker station is more susceptible to interference. 
The appearance of a beat sound may occur in the 
evening. A beat sound is created when two 
signals close in frequency interfere with each 
other. A common sign of this type of interference 
is a repetitious high-pitched sound that may over 
power the desired radio station. This sound is 
generated not only by sound signals but electrical 
waves as well.

2. The changing system may also be a source of 

noise. When diagnosing radio noise, do not over 
look the possibility of a problem with the vehicles 
generator.

DIAGNOSIS

STEP 1. Check the vehicles lighting system.

Q: Does the noise disappear when the vehicles 

headlights are turned "OFF"?
YES : 

Go to Step 2.

NO : 

Go to Step 3.

STEP 2. Check that the following actions 
disappear the noise.
Tune to a station with a stronger wave.

Q: Is there more noise than on radio in other 

vehicles?
YES : 

Consult the radio manufacturer's service 

center.

NO : 

 Check that there is no noise.

STEP 3. Check that the noise fades away when 
the vehicle harness is moved away from the 
radio (if the harness is not in the proper 
position).

Q: Does the noise fade away when the vehicle 

harness is moved any from the radio (If the 
harness is not in the proper position)?
YES : 

Consult the radio manufacturer's service 

center.

NO : 

If there is more noise than other radios, 
consult the radio manufacturer's service 
center.

INSPECTION PROCEDURE 8: Noise is Overpowering both AM and FM.

DIAGNOSIS

STEP 1. Check the state of the antenna.

Q:  Is the mast antenna assembled?

YES : 

Go to Step 2.

NO : 

Assemble the mast antenna. Check to see 
that the noise is gone.

STEP 2. Verify that the noise occur when the 
engine is stopped or the engine is running.

Q: Does noise occur when the engine is stopped or 

the engine is running?
When the engine is stopped : 

Go to Step 3.

When the engine is running : 

Check the vehicle's 

noise suppressor. (Refer to Inspection 
Procedure 11 

P.54A-169

.)

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STEP 3. Verify that the following actions 
disappear the noise.
(1) Tune to a station with a stronger wave.
(2) Extend the antenna completely (Mast antenna).
(3) Adjust the sound quality to suppress high tones.

Q: Is the noise eliminated?

YES : 

Consult the radio manufacturer's service 

center.

NO : 

Go to Step 4.

STEP 4. Verify that the radio is correctly 
grounded
The radio is connected to the ground with an assem-
bling screw.

Q: Is the radio correctly grounded?

YES : 

Go to Step 5.

NO : 

Consult the radio manufacturer's service 
center.

STEP 5. Check the connection of the antenna 
plug and radio and CD player.

Q:  Is the antenna plug thoroughly connected to the 

radio and CD player?
YES : 

Go to Step 7.

NO : 

Go to Step 6.

STEP 6. Verify that the noise is eliminated when 
the antenna plug is properly attached.

Q: Is the noise eliminated?

YES : 

Consult the radio manufacturer's service 

center.

NO : 

Go to Step 7.

STEP 7. Verify that the antenna is in good 
condition and is it properly mounted.

Q: Is the antenna in good condition and is it properly 

mounted?
YES : 

Consult the radio manufacturer's service 

center.

NO : 

Either repair or replace the antenna 
assembly. Check to see that the noise is 
gone.

INSPECTION PROCEDURE 9: Excessive Noise on AM and FM.

.

DIAGNOSIS
Radio reception can be affected by Radio Frequency 
(RF) emissions from a variety of sources. The distur-
bance is even greater if the station is weak or poorly 
tuned. FM reception is not as sensitive to distur-
bances as AM. AM reception is sensitive to electrical 
disturbances such as power lines, lightening and 
other types of similar electrical phenomena.

STEP 1. Check if the customer heard the noise 
under any of the following conditions.

• A motorcycle was passing.

• Lighting was flashing.

• Passed beneath a power line.

• Passed beneath a telephone line.

• Passed by a signal generator.

• Passed by any other sources of electrical noise.

• Passed under a bridge or through a tunnel.

Q: Did the noise occur during any of the 

circumstances listed above?
YES : 

The observed noise is normal.

NO : 

Go to Step 2.

STEP 2. Compare the customers radio to another 
identical model.
Operate the radio in a vehicle with a known good 
audio system of the same type as the customer's.

Q: Is there more noise on the customers radio?

YES : 

 Check all power and ground connections. If 

all connections are in good condition, 
consult the radio manufacturers service 
center.

NO : 

The observed noise is normal.

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INSPECTION PROCEDURE 10: Noise is Detected with Engine Running.

.

DIAGNOSIS

CAUTION

• Never connect a noise filter to the high ten-

sion cable (spark plug wire). Spark plug wires 
incorporate resistors which have the effect of 
suppressing noise. If a spark plug wire is 
found to be causing noise, it must be 
replaced.

• Confirm that the noise is not from an external 

source.

• Noise prevention should be performed by 

suppressing strong sources of noise first.

NOTE: Voltage surges can be induced in the electri-
cal system by the collapse of a field (i.e. When power 
is removed from the coil in an A/C compressor 
clutch). This induced voltage surge will radiate a 
Radio Frequency (RF) signal that is picked up by the 

audio unit. In the case of the compressor clutch a 
"pop" will be heard through the speakers. The capac-
itor, installed on this vehicle, will store the excess 
voltage and prevent the production of RF noise. This 
is because the capacitor will charge and discharge 
as the voltage fluctuates. This has the effect of 
"attracting" noise and bleeding it to ground without 
interfering with the normal flow of current through the 
system. 

DESCRIPTION OF NOISE CONDITIONS

CAUSE

SOLUTION

AM, FM: ignition noise 
(popping, snapping, 
cracking, buzzing)

• Increasing the engine 

speed causes the 
generator whine to 
speed up and the 
volume to decrease.

• Disappears when the 

ignition switch turned 
to "ACC", and engine 
is off.

• Electrical interference 

from the spark plugs.

• Engine noise.

• Check or replace the 

ground cable.

• Check or replace 

spark plug wires.

• Check or replace the 

noise capacitor.

Other electrical 
components

-

• Noise may intensify 

due to aging electrical 
components.

• Repair or replace the 

electrical components.

Static electricity (cracking, 
crinkling)

• Noise disappears 

when the vehicle is 
completely stopped.

• Noise is severe when 

the clutch is engaged.

• Noise occurs when 

parts or wiring move 
and contact vehicle 
body.

• Return parts or wiring 

to their proper 
position.

Static electricity (cracking, 
crinkling)

• Various noises are 

produced depending 
on the body part of the 
vehicle.

• This may be due to 

the recent removal of 
the front hood, 
bumpers, exhaust 
pipe and muffler, 
suspension, etc.

• Properly ground parts.

• Properly ground all 

body parts.

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INSPECTION PROCEDURE 11: Noise Appears During Vibration or Shocks.

DIAGNOSIS

STEP 1. Check radio and CD player connector D-06 and 
amplifier connector G-19 <with amplifier> for loose, 
corroded or damaged terminals, or terminals pushed back 
in the connector.
Q: Are radio and CD player connector D-06 and amplifier 

connector G-19 <with amplifier> in good condition?
YES : Go to Step 2.
NO :  Repair or replace the damaged component(s). Refer 

to GROUP 00E, Harness Connector Inspection 

P.00E-2

. Check that there is no noise.

AC204915AB

GROUND CABLE

ACX02360AB

GROUND CABLE

AC204170

CONNECTOR : D-06

CS

HARNESS SIDE

1
7

2
8

10

11

5

13

6

14

12

4

9

3

AC204179

CONNECTOR : G-19

AV

HARNESS SIDE

3 2

1110

4

1312

1
9

5

6

1615

7

8

1817

14