How TPMS Works

How TPMS Works
The TPMS (Tire Pressure Monitoring System) has six indicators; four tire indicators, a low pressure indicator, and a system indicator. When the TPMS control unit detects low pressure in a tire, or a problem in the system, it turns on the appropriate indicator(s).

^ If low tire pressure is detected, the low tire pressure indicator and the appropriate tire indicator(s) come on.
^ If a problem in the system is detected, the TPMS indicator comes on.
^ If low tire pressure and a problem in the system are detected, only the TPMS indicator comes on.

If the system is OK, the TPMS indicator, the low tire pressure indicator and the four tire indicators should come on when you turn the ignition switch ON (II), and then go off 2 seconds later. If they don't, there is a problem with the system.

If the system detects low pressure in any of the four tires, the low tire pressure indicator and the appropriate tire indicator(s) will come on, and the control unit will set one or more of these codes: DTC 11, 13, 15, 17. When the tire pressure returns to normal, the control unit will turn off the indicators and store the DTC(s). However, if the control unit detects a problem in the system during an indication of low tire pressure, it will turn off the low pressure and tire indicators, store the DTC(s), and turn on the TPMS indicator.

NOTE: Tire pressures will increase slightly as the temperature in the tires rises during driving at highway speeds. Pressures will also increase or decrease slightly with changes in outside air temperature. A temperature change of about 18 °F (10 °C) will change tire pressure by about 10 kPa (0.1 kgf/cm2, 1.5 psi). If the temperature drops and then rises, tire pressure could decrease just enough to turn on the low pressure and tire indicator(s), but later increase enough to turn them off. To resolve a complaint of such intermittent indications, confirm and clear the stored DTC(s) and check the tire pressures. Then explain to the customer how temperature changes can affect the system, especially when tire pressures are near the low end of the TPMS normal range - 168 to 220 kPa (1.7 to 2.2 kgf/cm2, 24 to 32 psi).

If a problem is detected in the system, the TPMS indicator will come on and stay on until the system returns to normal with most DTCs. If DTC 45, 51, 53, 55, 57, 81, 83 or 85 is set, the TPMS indicator will go off only when the ignition switch is turned off.

If a flat tire is replaced with the spare tire, and the flat tire is stored in the In-Bed Trunk, the low tire pressure indicator will stay on but the appropriate tire indicator will go off. This prevents the customer from thinking there is a problem with the spare tire. When the flat tire is taken out of the vehicle for repair, the TPMS indicator will come on (DTC 32, 34, 36 or 38) because the system is no longer receiving the signal from the tire's transmitter.

Problems That are Not System Faults
^ Tire Sealant
Fluid sealant used to repair a punctured tire can damage the tire pressure sensor mounted on each wheel. It can prevent the system from detecting the correct tire pressure, which sets a DTC 11, 13, 15, or 17 even though the system is normal.
^ Cold Weather
When the weather is extremely cold - about -40 °F (-40 °C) or colder - the output of the lithium battery in each tire pressure sensor may drop far enough that the control unit sets a DTC for low battery voltage (31, 33, 35, or 37) even though the system is normal.
^ Non-TPMS Wheels
Vehicles equipped with TPMS must use wheels made for the system. Every TPMS wheel has an exclusive mark; do not use any other type of wheel.

How a Diagnostic Trouble Code (DTC) is Set
^ When the system detects a problem, the TPMS control unit sets a code, but shifts to fail-safe mode, and will not alert the driver to low tire pressures.
^ If the TPMS control unit loses power, or fails, the TPMS indicator will come on, but no DTC will be set.
^ The memory can hold all the DTCs that could possibly be set. However, when the same DTC is detected more than once, the most recent one overwrites the previous one, so only the latest DTC of each type is stored.
^ DTCs are indicated in ascending order, not in the order they occurred.
^ Set DTCs are stored in the EEPROM (nonvolatile memory), they cannot be cleared by disconnecting the battery. To clear a DTC, connect the HDS (Honda Diagnostic System) to the data link connector (DLC), and follow the screen prompts.