Toyota Sienna Service Manual: Identification of noise source
1. Radio Description
- Radio frequency band
- Radio broadcasts use the radio frequency bands
shown in the table below.

- Service area

- The service areas of AM and FM broadcasts are
vastly different. Sometimes an AM broadcast
can be received very clearly but an FM stereo
cannot. FM stereo has the smallest service area,
and is prone to pick up static and other types of
interference such as noise.
- Radio reception problems
HINT:
In addition to static, other problems such as
"phasing", "multipath", and "fade out" exist. These
problems are not caused by electrical noise, but by
the radio signal propagation method itself.

- Phasing
AM broadcasts are susceptible to electrical
interference and another kind of interference
called phasing. Occurring only at night, phasing
is the interference created when a vehicle
receives 2 radio wave signals from the same
transmitter. One signal is reflected off the
ionosphere and the other signal is received
directly from the transmitter

- Multipath
Multipath is a type of interference created when
a vehicle receives 2 radio wave signals from the
same transmitter. One signal is reflected off
buildings or mountains and the other signal is
received directly from the transmitter.

- Fade out
Fade out is caused by objects (buildings,
mountains, and other such large obstacles) that
deflect away part of a signal, resulting in a
weaker signal when the object is between the
transmitter and vehicle. High frequency radio
waves, such as FM broadcasts, are easily
deflected by obstructions. Low frequency radio
waves, such as AM broadcasts, are much more
difficult to deflect.
- Noise problem
Technicians must have a clear understanding about
each customer's noise complaint. Use the following
table to diagnose noise problems.

HINT:
If the noise does not match the examples above, refer to the
descriptions about phasing and multipath.
1 VEHICLE BROUGHT TO WORKSHOP
2 INSPECT BATTERY VOLTAGE
Standard voltage:
11 to 14 V
If the voltage is below 11 V, recharge or replace the battery
before proceeding.
3 BASIC INSPECTION
Turn ...
HINT:
Before inspecting the suspected areas listed in the table
below, check the fuse and relay.
Before inspecting the suspected areas listed in the table
below, check for DTCs.
...
Other materials:
High pitched horn
COMPONENTS
REMOVAL
1. REMOVE FRONT BUMPER COVER
2. REMOVE HIGH PITCHED HORN
Disconnect the connector.
Remove the bolt and horn.
INSPECTION
1. INSPECT HIGH PITCHED HORN
Apply battery voltage and check operation of the
horn, as shown in the table.
Standard ...
Disassembly
1. Remove park/neutral position switch assembly
(A) remove the nut, washer and control shaft lever.
(B) using a screwdriver, unstake the nut stopper, and
remove the lock nut and nut stopper.
(c) Remove the 2 bolts and pull out the park/neutral
position switch.
2. REMOVE BREATHER PLUG H ...
Operation check
1. INPUT SIGNAL CHECK
Connect the intelligent tester to the DLC3.
Check the cruise control main switch using the
DATA LIST function in the intelligent tester (ONOFF,
CANCEL, - (COAST)/SET, + (ACCEL)/RES
(RESUME), and MODE).
2. INSPECT MODE SWITCH
Turn the ...