Tire Pressure Monitoring Systems: The Ins and Outs of Indirect and Direct TPMS - Page 4 of 4

Tire Pressure Monitoring Systems: The Ins and Outs of Indirect and Direct TPMS

TPMS RELEARNING PROCEDURES
This is the part that causes the most confusion and headaches. On vehicles where the TPMS has to know the wheel position of each sensor, the system must be programmed or taught the location of each sensor. On a few, such as the new Acura MDX, the system will automatically learn each sensor location. But on most Asian import applications, each sensor has a code that is programmed into the TPMS control module at the factory.

If one or more of these original equipment sensors is later replaced with another OEM or aftermarket sensor, the new sensor code(s) must be manually programmed into the TPMS system using a scan tool. That means a trip to the dealer if you do not have a factory scan tool or an aftermarket scan tool with the appropriate software in your shop. Vehicles that currently require this kind of reprogramming include most Hyundai, Infiniti, Kia, Lexus, Mitsubishi, Nissan, Subaru, Suzuki and Toyota models.

Removing a wheel from a vehicle when doing brake or suspension repairs doesn’t require any special procedures on TPMS-equipped vehicles. Just remount the wheel in the same location as before when you’ve finished the repairs. But if you’re rotating tires, or moving a wheel from one location to another (as when troubleshooting a steering pull or vibration problem), the TPMS will have to be taught the new position of each sensor. This will require a scan tool or a special TPMS test/relearn tool.

When removing more than one wheel at a time from a TPMS-equipped vehicle, use a piece of chalk to mark each wheel’s position (RF, LF, RR, LR). That way, you won’t forget which wheel went where and accidentally mount the wheels in the wrong locations.

Aftermarket TPMS testers are available from a number of sources and typically sell for $500 or less. Most of these testers cover a wide range of makes and models (import and domestic), but some may be limited to specific models or types of sensors (such as sensors that operate in continuous mode or modulated mode only).

The tester communicates electronically with the sensors and TPMS. The unit typically activates the pressure sensors so they will broadcast a signal. The unit then programs the TPMS module or receiver in the vehicle so it will recognize which sensor is which (RF, LF, RR, LR). The tool can also be used to verify the operation of each individual sensor and troubleshoot TPMS faults. Many of these tools have a USB port that allows the tool’s software to be updated as needed, and to download information from the tool to a PC for printing or recording. For more advanced diagnostics involving communication problems between the TPMS module in the vehicle and the PCM or keyless entry system, an OEM scan tool or aftermarket professional-grade scan tool with OEM-level software will be needed. A scan tool is also needed for most indirect (ABS) TPMS systems, for diagnostics and resetting the system.

All TPMS systems have self-diagnostic capability and will set a diagnostic trouble code (DTC) if a pressure sensor fails. If you find DTCs for all four pressure sensors, it means the TPMS module has forgotten the locations of the sensors because the vehicle battery has been disconnected or has run down. It could also mean there is a problem with the TPMS or keyless entry system receiver. Refer to the diagnostic flow charts in your service literature when troubleshooting these types of DTCs to avoid unnecessarily replacing parts.

TPMS RESET
If you add air to a low tire, or have repaired or replaced one or more tires, refer to the owner’s manual or service literature to see if a reset procedure is required. This may involve pressing a system reset button and/or driving the vehicle in a straight line above a specified speed for a specified length of time to complete the system reset.

On many Toyotas, for example, there is a reset button inside the glove box. To reset the system, turn the ignition ‘on’, then press and hold the reset button for three seconds. When the TPMS warning light blinks three times, the system is reset. Wait at least five seconds before turning the ignition ‘off’ so the system will recognize the new tire pressure readings.

On a Toyota Land Cruiser, there is a Main/2nd switch that allows the vehicle owner to use two different sets of wheels and tires (on-road and off-road). The switch tells the TPMS which set of sensors to look at using the ID numbers that were programmed in at the factory.

On a 2006 Volkswagen Jetta, the TPMS won’t reset unless the car has been parked for at least 20 minutes. The car must then be driven at 16 mph or faster for at least seven minutes for the system to reset and relearn the new pressure settings. Only then will the TPMS warning light go out.

OTHER SERVICE ISSUES
The TPMS is calibrated for the original equipment wheels and tires, so replacing the OEM parts with aftermarket parts may cause some problems. As mentioned earlier, the OEM sensors may not fit certain aftermarket wheels. Also, if the tire sizes are different and require a different inflation pressure, the TPMS may have to be reprogrammed for the new pressure using a factory scan tool or equivalent (if this is even possible).

If a vehicle has an indirect TPMS with no tire pressure sensors, replacing the original tires and/or wheels with different sizes may upset the operation of TPMS. “Plus sizing” (installing lower-profile tires on larger diameter rims to maintain the same overall tire diameter) may be necessary for the TPMS to function properly if the replacement wheels are larger than the original wheels.

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