Understanding Tire Pressure Monitoring System (TPMS) Relearn Procedures
When servicing a direct Tire Pressure Monitoring System (TPMS), a TPMS system relearn is often required after procedures such as air pressure adjustment, tire rotation, or sensor replacement. These relearn procedures, which vary by manufacturer, ensure the TPMS functions correctly. Technicians need to determine when a relearn is necessary to put the vehicle in "learn" mode. There are three main types of relearn procedures: auto relearn, stationary (manual), and OBD (On-Board Diagnostics). Some vehicles may use a combination of these. The TPMS relearn process is created by the vehicle manufacturer and involves a series of specific steps. By following the correct procedure, the entire TPMS system can be restored to proper working order. With the right TPMS tools and knowledge, TPMS relearn procedures can be easy to service.
Types of TPMS Relearn Procedures
Auto Relearn
This type of relearn is often the simplest. The vehicle automatically learns the new sensor IDs after a short driving period. Specific conditions, such as a certain speed or duration of driving, may need to be met for the relearn to complete.
Stationary (Manual) Relearn
This procedure requires a specific sequence of actions, often involving inflating or deflating tires in a particular order, or using the vehicle's controls to initiate the relearn process.
OBD Relearn
This method uses the vehicle's OBD port to directly program the new sensor IDs into the vehicle's ECU (Engine Control Unit). This typically requires a TPMS scan tool with OBD capabilities.
The Importance of Relearn Procedures
The TPMS relies on accurate sensor data to alert the driver to underinflated tires. When sensors are moved or replaced, the system needs to be updated with the new sensor locations and IDs. Without a proper relearn, the TPMS may not function correctly, leading to inaccurate readings or failure to detect low tire pressure.
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Specific Vehicle Considerations: Toyota and Lexus
Toyota and Lexus vehicles often require an OBD relearn procedure. A potential issue arises with the "SET" button, located below the steering wheel or in the glove box of some Toyota models. Pressing this button prompts the system to locate the sensor IDs that are already stored.
The Role of the "SET" Button
The "SET" button is useful in scenarios like tire rotation (especially with different front and rear tire pressures), tire pressure adjustments, tire size changes, or tire replacements. However, it's crucial to understand its limitations.
When OBD Relearn is Necessary
When replacing a sensor or installing a second set of wheels, an OBD relearn becomes mandatory. This is because the OBDII module connection programs the new sensor ID numbers directly into the vehicle’s ECU.
Addressing Conflicts with the "SET" Button
If the "SET" button is pressed when a relearn is actually required (e.g., after sensor replacement), the ECU must be unlocked for the relearn procedure to work correctly. Advanced TPMS scan tools, such as the VT56, often have an "UNLOCK ECU" function within their service TPMS menu to deactivate the "SET" button's influence.
Troubleshooting Relearn Failures
Even when all steps are performed correctly, the relearn procedure can sometimes fail. Here are some potential causes and troubleshooting tips:
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Interference Issues
Interference between the sensor and the vehicle’s ECU can occur, particularly in larger trucks like the F-Series.
Ensuring Proper Procedure
Make sure to follow each step precisely. For example, some Ford models require pressing the start button twice (without pressing the brake) to enter RUN mode (Ignition ON/Engine OFF).
Environmental Factors
Lower all windows, turn off the radio, and open the doors to minimize potential interference during the relearn process.
Audible Confirmation
Listen for a chirp sound as an indication of success during certain steps (e.g., steps 6 or 8). If the chirp is absent, the relearn procedure likely did not work.
OBD Relearn Advantages
The OBD relearn procedure offers several advantages over manual relearn methods. The manual relearn typically involves a significant number of steps (ranging from 7 to 11), which can be time-consuming for technicians.
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Tool Requirements
Note that only a few advanced TPMS diagnostic scan tools possess the necessary protocols to perform an OBD relearn.
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