Identification Of Noise Source

WARNING: This page is about a different car, the 2006 Toyota Camry Solara. However, it is still accessible from the selected car via links, so may be relevant.

RADIO WAVE BAND
1. The radio wave bands used in radio broadcasting are as follows:
  
  Fig 1: Identifying Radio Wave Band
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  
  HINT:
  - LF: Low Frequency
  - MF: Medium Frequency
  - HF: High Frequency
  - VHF: Very High Frequency
SERVICE AREA
1. There is a great difference in the size of the service areas for AM and FM broadcasting. Sometimes an FM stereo broadcast cannot be received even though AM can be received very clearly. FM stereo has the smaller service area, and it also picks up static and other types of interference ("noise") easily.
  
  Fig 2: Identifying Service Area Of AM And FM Broadcasting
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
RECEPTION PROBLEMS
HINT:

Besides the problem of static, there are other problems, such as "phasing", "multipath" and "fade out". These problems are caused not by electrical noise but by the nature of the radio waves themselves.
1. Phasing
  Besides electrical interference, AM broadcasts are also susceptible to other types of interference, especially at night. This is because AM radio waves bounce off the ionosphere at night. These radio waves then interfere with the signals that reach the vehicle's antenna directly from the same transmitter. This type of interference is called "phasing".
  
  Fig 3: View Of Phasing
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Multipath
  Interference caused by reflection of radio waves against obstructions is called "Multipath". Multipath occurs when radio signals emitted from the broadcast transmitter antenna are reflected against tall buildings or mountains and interfere with other signals which are to be received directly.
  
  Fig 4: View Of Multipath
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. Fade Out
  FM radio wave tends to be reflected against obstructions such as tall buildings or mountains because FM frequency is higher than AM. For this reason, FM signals often seem to gradually disappear or fade away as the vehicle goes behind those obstructions. This phenomenon is called "fade out".
  
  Fig 5: View Of Fade Out
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

NOISE PROBLEMS

It is very important for technicians to clearly understand a customer's claim about noise. Use the following table to diagnose the phenomena.

NOISE PROBLEMS CONDITIONS AND PROBABLE CAUSES NOISE PROBLEMS CONDITIONS AND PROBABLE CAUSES

Radio wave	Condition in which noise occurs	Probable cause
AM	Noise occurs at a specific place.	Strong possibility of foreign noise.
AM	Noise occurs when listening to faint broadcasting.	The same program may be broadcasted from some local stations. If the program is the same, one of those may be tuned in.
FM	Noise occurs only at night.	Strong possibility of an interfering beat from a distant broadcast.
FM	Noise occurs at a specific place during driving.	Strong possibility of multipath noise and phasing noise caused by changes of FM frequency.

HINT:

If the condition when the noise occurs does not meet any of the above, find out the cause based on "Reception Problems". Refer to the description about multipath and phasing mentioned previously.

Identify the conditions under which the noise occurs, and check the noise filter on the relevant part.

NOISE CONDITIONS REFERENCE NOISE CONDITIONS REFERENCE

Conditions under which noise occurs	Noise type
Noise increases when the accelerator pedal is depressed, but stops when the engine is stopped.	Generator noise
Noise occurs during A/C or heater operation.	Blower motor noise
Noise occurs when the vehicle accelerates rapidly on an unpaved road or after the ignition switch is turned to the ON position.	Fuel pump noise
Noise occurs when the horn switch is pressed and released or when pressed and held.	Horn noise
Quiet noise occurs while the engine is running, but stops when the engine is stopped.	Ignition noise
Noise occurs synchronously with the blink of the turn signal.	Flasher noise
Noise occurs during window washer operation.	Washer noise
Noise occurs while the engine is running, and continues even after the engine is stopped.	Water temperature sensor noise
Noise occurs during wiper operation.	Wiper noise
Noise occurs when the brake pedal is depressed.	Stop light switch noise
Others	Static electricity stored on the vehicle

Reference:

Make sure first that there is no noise from the outside. Failure to do so makes noise source detection difficult and may lead to a misdiagnosis.
Noise should be removed in descending order of loudness.
Tuning the radio so that no station is received makes the noise more noticeable, making the recognition of the phenomenon easier.