TPMS System Description - Low Pressure Detection Methods

Low Pressure Detection Methods 

The Indirect TPMS establishes a baseline tire pressure reading using the wheel speed sensors and indirectly monitors tire pressure to detect pressure loss in any of the four tires.

The system uses these two methods to determine loss of tire pressure:

• Wheel speed differential
• Peak tire resonance.

Both methods make use of outside temperature sensor data to correct calculated tire pressures for ambient temperature variations.

Wheel Speed Differential 

When monitoring tire pressure using the wheel speed differential method, the TPMS module compares the speed of the wheels in three different configurations:

• Diagonal comparison between the front and rear wheels
• Comparison between the two front and two rear wheels
• Comparison between the two right and two left wheels

Courtesy of HONDA, U.S.A., INC.

Tire diameter shrinks as the tire deflates, causing the wheel speed to increase.Consequently, if the difference in wheel speeds exceeds the threshold, the low tire pressure/TPMS indicator turns on as shown in the step-to-step diagram below.

Courtesy of HONDA, U.S.A., INC.

Peak Tire Resonance 

Peak resonance frequency value learned during calibration becomes the initial value. The peak resonance frequency method compares the initial peak resonance frequency value of the two front tires and the present peak resonance frequency value of the two front tires, and detects reduced pressure of the two front tires. If the present peak resonance value becomes equivalent to 25% reduced air pressure, the low tire pressure/TPMS indicator turns ON as shown in the step-to-step diagram below.

Resonance frequency is corrected based on the outside air temperature sensor information, because resonance frequency is changed by the outside air temperature.

Courtesy of HONDA, U.S.A., INC.

Courtesy of HONDA, U.S.A., INC.

The TPMS module compares the peak resonance values learned at calibration. If the value drops below a 25% pressure threshold, the low tire pressure/TPMS indicator turns on.

Temporary Suspension 

Certain situations, such as when the vehicle is turning, accelerating, decelerating, or braking will temporarily prevent the system from monitoring tire pressures due to varying tire loads. The TPMS module uses other devices such as the lateral acceleration sensor, the yaw sensor, the steering angle sensor, the master cylinder pressure sensor and the PCM data to determine how the vehicle is being driven.