Sep. 26, 2024
The primary function of the Tire Pressure Monitoring System (TPMS) is to inform the driver about the tire pressure status. During normal operation, the TPMS alerts the driver when the PSI reading of one or more tires drops below 25% of the vehicle's specified limit. When a tire sensor detects low pressure, it transmits a radio frequency (RF) signal of either 315 or 433 MHz to the vehicle's ECU. The ECU then assesses whether the pressure is below the threshold and activates a TPMS warning symbol or a position-specific display, depending on the vehicle model.
TPMS systems are categorized into two types: direct and indirect.
Direct TPMS utilizes sensors located within each wheel to provide real-time pressure data directly to the vehicle's ECU. This type is commonly found in Asian, domestic, and European vehicles.
In contrast, Indirect TPMS relies on the ABS system to monitor wheel speed as a means of estimating tire pressure. Indirect systems are typically used in certain Asian and European vehicles.
The TPMS warning light activates when a tire is under-inflated and should turn off once the tire is inflated to the recommended pressure as indicated on the vehicle's door placard. Upon starting the vehicle, the TPMS icon will illuminate for a few seconds; if it remains on, this indicates that one or more tires are at least 25% below the recommended pressure. A flashing light for about one to two minutes signals a malfunction in the TPMS system.
Several factors can trigger a TPMS warning light to illuminate or flash. Common issues include:
- Dead sensor batteries
- Physical damage, corrosion, or missing components in the valve
- Malfunctions in the TPMS system's voltage supply, wiring, or internal electronics
- Improperly performed relearn procedures after tire servicing or rotation
It's crucial to check the TPMS system before servicing a customer's vehicle. To diagnose the issue, use a TPMS diagnostic tool. You can either manually select the vehicle's make, model, and year or quickly scan the VIN barcode located on the vehicle's doorjamb to access the sensor information.
To reset a TPMS system for vehicles with direct TPMS, follow these steps:
1. Use a TPMS diagnostic tool to trigger and read the sensor information before servicing the vehicle.
2. Carry out the necessary service on the vehicle's wheels, such as adjusting air pressure, rotating tires, or replacing sensors.
3. After completing the service, use the TPMS diagnostic tool to perform the correct relearn procedure to reset the TPMS system.
For vehicles with indirect TPMS, follow the appropriate initialization procedure. This may involve using a TPMS diagnostic tool to identify the necessary steps for resetting the system.
Vehicles with direct TPMS systems contain TPMS sensors that must be replaced if they are malfunctioning before a relearn procedure can be executed. A damaged sensor can be replaced with either an OE sensor or an aftermarket option. Aftermarket TPMS sensors come in various types, including universal, configurable, and programmable sensors. OE, universal, and configurable sensors come with new sensor IDs pre-encoded and require activation using a TPMS diagnostic tool. Programmable TPMS sensors necessitate a diagnostic tool to create new sensor IDs or transfer IDs from the old sensor.
After servicing a vehicle's direct TPMS system—such as adjusting air pressure, rotating tires, or replacing sensors—a TPMS relearn must be performed. This process enables the vehicle's ECU to recognize the IDs of each sensor in the wheels. Completing the relearn clears TPMS diagnostic fault codes and ensures the system operates correctly.
Relearn procedures differ by manufacturer, so technicians must be familiar with the appropriate method to enter learn mode. The three main types of relearn procedures are auto relearn, stationary, and OBD, with some vehicles potentially using a combination of these methods. Indirect TPMS systems require an initialization procedure, which may involve a TPMS tool to determine the steps needed to reset the system.
According to AMRA, among Asian, Domestic, and European vehicles with direct TPMS systems, the breakdown of relearn procedures is as follows: 38% use auto relearn, 27% use OBD, and 35% use stationary.
An auto relearn procedure allows a vehicle to learn single or multiple TPMS sensor IDs without needing a TPMS tool for the relearn process. After a technician adjusts the inflation pressure, rotates tires, or replaces sensors, the TPMS system will reset itself once the vehicle has been driven for a certain period. However, it is advisable to use a TPMS tool to trigger each sensor before servicing the tires or wheels to ensure they are functioning correctly.
For example, the auto relearn procedure for a 2008 Dodge Charger involves:
- Inflating all tires
- Driving the vehicle for 20 minutes
The stationary relearn procedure, also known as manual relearn, allows new TPMS sensor IDs to be transferred to the vehicle's ECU without driving the vehicle. This process requires a TPMS activation tool to trigger the sensors while the vehicle is in learn mode, using either a TPMS diagnostic tool or a diagnostic scan tool. The vehicle communicates with the ECU via a radio frequency (RF) signal to identify the location of each sensor.
For example, the stationary relearn procedure for a 2014 Ford Escape with standard ignition involves the following steps:
1. Inflate all tires.
2. Turn the ignition off.
3. Press and release the brake pedal.
4. Cycle the ignition from "off" to "run" three times, ending in "run."
5. Press and release the brake pedal again.
6. Turn the ignition off.
7. Cycle the ignition from "off" to "run" three times, ending in "run."
8. The horn will sound twice.
9. Use the tool to activate the left front sensor; a single horn sound will confirm activation.
10. Repeat for the right front sensor, right rear sensor, and left rear sensor.
The OBDII relearn procedure involves using a TPMS diagnostic tool to transfer new sensor IDs directly to the vehicle's ECU. This process requires triggering each TPMS sensor, connecting the tool to the vehicle's OBD port, and following the step-by-step instructions provided by the tool. Most Asian and specialty European vehicles necessitate an OBD relearn.
For example, the OBDII relearn procedure for a 2011 Toyota Camry includes the following steps:
1. Inflate all tires.
2. Read all sensor IDs using the TPMS diagnostic tool.
3. Connect the tool to the OBDII port.
4. Reset the ECU with the tool.
5. Turn the ignition OFF, then ON.
6. Drive the vehicle at 12 mph for up to 5 minutes.
Manual and stationary relearn systems often involve multiple steps, making the TPMS relearn process time-consuming and complex. While TPMS diagnostic tools provide step-by-step instructions for auto, stationary, and OBD relearns, the procedures can still be lengthy and intricate. OBD relearn procedures are increasingly becoming the standard in shop environments for several reasons. Primarily, they simplify the process, as the same procedure can be applied across various vehicle types. Additionally, OBD relearn saves time and reduces confusion for technicians, requiring fewer steps to complete.
According to the Automotive Maintenance & Repair Association (AMRA), 62% of vehicles need a TPMS diagnostic tool, with 27% requiring OBD functionality. Therefore, having a reliable TPMS diagnostic tool with comprehensive OBD coverage is essential for keeping pace with the evolving TPMS industry.
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