What is TPMS?
The tire pressure monitoring system's (TPMS) primary function is to make the driver aware of the state of tire pressure within the wheels. Under normal system operations, the TPMS system will alert the driver when one or more affected tires PSI reading falls below 25 percent of the placard. When the tire sensor indicates “low tire pressure”, it sends a radio frequency (RF) signal of 315 or 433 MHz to the ECU on the vehicle that determines if the pressure is below the threshold, which then will indicate a TPMS symbol or position-specific display, depending on the vehicle.
Direct vs. Indirect TPMS systems
There are two types of TPMS systems: direct TPMS and indirect TPMS. Direct TPMS systems use TPMS sensors inside the wheel to accurately report pressure data to the vehicle’s ECU in real time. Direct systems include Asian, domestic and European vehicles. An indirect TPMS system uses an ABS system to monitor the speed of the wheel in order to approximate tire pressure. Indirect systems include Asian and some European vehicles.
How does the TPMS dashboard light/warning indicate?
The light will illuminate when a tire is low, and should eventually go out after a tire has been inflated to its recommended pressure according to the vehicle’s door placard. After starting a vehicle, a TPMS icon will turn on for a few seconds, however, if it stays on, it indicates that one or more of the tires on the vehicle is at least 25 percent below the recommended pressure. If the light flashes for approximately one to two minutes, it indicates there is a malfunction in the TPMS system.
There are numerous situations that can cause a TPMS warning light to come on or flash. Some TPMS problems include:
- Sensor batteries may be dead.
- Valve itself may have physical damage, corrosion or missing components.
- The TPMS system voltage supply, wiring or internal electronics may not be functioning properly.
- The tires were serviced or rotated and the relearn procedure was not properly performed.
It is important check the TPMS system before working on a customer’s vehicle. Using a TPMS diagnostic tool, select the vehicle’s make, model and year manually or, for faster service, scan the vehicle’s VIN barcode located on the placard on the vehicle door jamb to read the sensor information.
Steps to reset TPMS system
The proper steps to reset a TPMS system for a vehicle with direct-TPMS:
- Use a TPMS diagnostic tool to trigger and read sensor information before working on vehicle.
- Perform service to vehicle’s wheels (air pressure adjustment, tire rotation, replace sensors, etc.).
- After the service has been performed, use a TPMS diagnostic tool to perform the correct relearn procedure to reset the TPMS system.
The proper steps to reset a TPMS system for a vehicle with indirect TPMS:
- Perform the correct initialization procedure. This may require a TPMS diagnostic tool to find the steps involved to reset the system.
Replacing TPMS sensors
Vehicles with direct-type TPMS systems are equipped with TPMS sensors. If a TPMS sensor is not working, it must be replaced before a relearn procedure can be performed. The damaged TPMS sensor can be replaced by an OE sensor or an aftermarket sensor. There are different types of aftermarket TPMS sensors, including universal, configurable and programmable sensors. OE sensors, universal and configurable sensors have new sensor ID’s already encoded within the sensor and need to be activated by using a TPMS diagnostic tool. Programmable TPMS sensors require a TPMS diagnostic tool to create new sensor ID’s or transfer sensor ID’s from the old sensor.
Relearn procedures
When service has been performed to the vehicle’s direct TPMS system, such as air pressure adjustment, tire rotation or replacement of sensors, vehicles require a TPMS system relearn to be performed. A relearn allows the vehicle’s ECU to see the ID’s of each sensor in each wheel. Completing the relearn procedure clears TPMS diagnostic fault codes and allows the vehicle’s TPMS system to function properly.
Relearn procedures vary by manufacturer, so a technician must know which proper relearn procedure is necessary to put the vehicle in learn mode. Although relearn procedures differ from manufacturer to manufacturer, the three types of relearn procedures are auto relearn, stationary and OBD. Furthermore, some vehicles may use a combination of two or more relearn types. Indirect TPMS systems use an initialization procedure which may require a TPMS tool to figure out the steps involved to reset the system.
Auto relearn procedure
An auto relearn procedure is when a vehicle has the ability to learn single or multiple TPMS sensor IDs without the need of performing the relearn procedure with a TPMS tool.
Furthermore, a technician can adjust the inflation pressure, rotate or replace sensors and the TPMS system will reset itself after the vehicle has been driven for a period of time. However, before servicing the tires/wheels, it is always recommended to use a TPMS tool to trigger each of the vehicle's sensors to make sure they are working properly.
For example, a 2008 Dodge Charger requires the following auto relearn procedure:
- Inflate all tires.
- Drive for 20 minutes.
Stationary relearn procedure
A stationary relearn (sometimes called manual) procedure allows new TPMS sensor IDs to be transferred to the vehicle’s ECU without driving a vehicle. This type of relearn procedure requires a TPMS activation tool to trigger the sensors when the vehicle is in learn mode either by using a TPMS diagnostic tool or a diagnostic scan tool. The vehicle then uses a radio frequency (RF) signal to communicate with the vehicle’s ECU to establish which sensor is in which specific location.
For example, a 2014 Ford Escape (with standard ignition) requires the following stationary relearn procedure:
- Inflate all tires.
- Turn ignition off.
- Press and release brake pedal.
- Cycle ignition from “off” to “run” three times ending in “run.”
- Press and release brake pedal.
- Turn ignition off.
- Cycle ignition from “off” to “run” three times ending in “run.”
- Horn sounds twice.
- Use tool to activate left front sensor.
- Single horn will sound.
- Repeat for right front sensor, right rear sensor, left rear sensor.
OBD-II relearn procedure
An OBD-II relearn procedure requires a TPMS diagnostic tool to transfer new sensor IDs directly to the vehicle’s ECU. The user will need to trigger each TPMS sensor, connect to the vehicle’s OBD port, then follow the step-by-step instructions on the tool. The new TPMS sensor IDs are then transferred to the vehicle. Most Asian and specialty European vehicles require OBD relearn.
For example, a 2011 Toyota Camry requires the following OBDII relearn procedure:
- Inflate all tires.
- Read all sensor IDs using TPMS diagnostic tool.
- Connect tool to OBD-II port.
- Reset ECU with tool.
- Turn ignition OFF, then ON.
- Drive at 12 mph for up to five minutes.
The importance of OBD relearn
Manual and stationary relearn systems can sometimes take several steps to relearn the TPMS system. TPMS diagnostic tools have the step-by-step instructions for auto, stationary and OBD relearn, however, the steps involved can be long and complicated. OBD relearn procedures are becoming standard in a shop environment for many reasons. First and foremost, it is the easier to work with since the same procedure can be performed no matter what the vehicle type is. Secondly, OBD relearn saves time and confusion for the technician since there are less steps to perform. According to amra.org, 62 percent of vehicles require a TPMS diagnostic tool and 27 percent require OBD functionality. It is important to have a reliable TPMS diagnostic tool with excellent OBD coverage to keep up with the growing industry of TPMS.
Information provided by: ATEQ TPMS Tools
