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 while, indirectly, monitoring 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
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.
Peak Tire Resonance
Peak resonance values are learned during calibration and become the reference values for pressure monitoring. When using the frequency resonance method, the TPMS module compares the peak resonance values between all four tires and the two front tires.
If the present values have dropped below a 25% pressure threshold, the low tire pressure/TPMS indicator turns ON as shown in the step-to-step diagram below.
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.