System Description

WARNING: This page is about a different car, the 2008 Toyota RAV4. However, it is still accessible from the selected car via links, so may be relevant.

DESCRIPTION OF SYSTEM
1. Each tire pressure warning valve and transmitter is equipped with a tire pressure sensor and a transmitter and is installed in each tire and wheel. The sensor measures the tire pressure. The measured value and transmitter ID are transmitted to the tire pressure warning antenna and receiver on the body as radio waves and then sent to the tire pressure warning ECU from the tire pressure warning antenna and receiver. If the transmitter ID has already been registered, the ECU compares the measured air pressure value with the standard value. When the value is less than the standard value registered on the tire pressure warning ECU, the warning light on the combination meter comes on.
  
  Fig 1: Identifying Tire Pressure Warning System Description
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

INITIAL CHECK

After the ignition switch is turned ON, the tire pressure warning light comes on for 3 seconds and then goes off.

HINT:

If the tire pressure warning light does not come on for 3 seconds, troubleshoot the tire pressure warning light circuit.

SYMPTOM CHART

Trouble Area	Proceed to
Tire pressure warning light circuit	TIRE PRESSURE WARNING LIGHT CIRCUIT

Fig 2: Tire Pressure Warning Light Blinking Pattern

WHEN TIRE PRESSURE WARNING LIGHT IS LIT
1. When the tire pressure warning light does not go off, or when it comes on during driving, check the tire pressure. If the tire pressure warning light comes on within several hours to adjusting the tire pressure, the tire may have a slow air leak.
2. Under the following conditions, the system may not function properly.
  - Facilities or devices that use similar radio frequencies are located in the vicinity of the vehicle.
  - A radio device of similar frequency is used in the vehicle.
  - A large amount of snow or ice is stuck to the vehicle, especially onto the wheels and around the wheel wells.
  - The battery of the transmitter has been depleted.
  - Tires without a tire pressure warning valve and transmitters are used.
  - Tire chains are used.
  - If any wheels other than the specified ones are used, the system may not function properly because interference may prevent the radio waves from being correctly transmitted from the tire pressure warning valve and transmitter.
  - A type of film that affects radio waves is attached to the windows.
  - Depending on the tire type, the tire pressure warning system may not function properly even though the specified wheels are used.
  - The tire pressure is abnormally high (absolute pressure: 600 kPa (6 kgf/cm² , 87 psi) or more; relative pressure: 500 kPa (5 kgf/cm² , 72.5 psi) or more).
3. The average usage life of the grommets of the tire pressure warning valve and transmitter is approximately 10 years, at which time it must be replaced.
  If a tire pressure warning valve and transmitter is removed from a wheel, replace the grommets.
4. After removing and installing the ECU or a sensor, check for DTCs and check that it is a normal system code.

FUNCTION OF COMPONENTS

Components	Function
Tire pressure warning valve and transmitter	Combined as a single unit with a disc wheel air valve, it measures tire pressure and temperature and transmits an ID number for measurement value and identification Battery is built into valve
Tire pressure warning antenna and receiver	Receives necessary signals from tire pressure warning valve and transmitter and transmits them to tire pressure warning ECU
Tire pressure warning ECU	Receives signal from receiver and identifies it as vehicle's own signal. If measured value is equal to or lower than specified value, it transmits a signal so that the tire pressure warning light on the combination meter turns on.
Tire pressure warning light	Located in the combination meter, it informs driver of lowered tire pressure and system failure