How the Subaru Tire Pressure Monitoring System TPMS works

The Subaru Tire Pressure Monitoring System (TPMS)
an unofficial information page to help you understand the tire pressure monitoring system

US Government (NHTSA) Safety Regulations require all new 4-wheeled vehicles weighing 10,000 pounds or less to be equipped with a tire pressure monitoring system detecting  25% drop in tire pressure by the 2008 model year. A TPMS was required by Congress in the 'Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act' of 2000.

Quick note - after adding air to tires please drive the car app 5 miles to give the sensors time to reset. The monitors will need to be re-synced when tires or wheels are replaced.

what models is it in  -  how it works  -  inflating  -  cold temperature  -  replacing a monitor - using nitrogen wheel and valve images  -  warning light

subaru tire pressure monitor information sticker
Subaru tire pressure monitor information sticker on 2010 models

Please read- this unofficial independent Subaru research site by Joe Spitz is designed to help you learn about Subarus. It is not sponsored, authorized,  supported or approved by Subaru or any dealer, and is not connected to or affiliated with, any dealer. Always contact your local dealer. Inspect any vehicle prior to purchasing. Information subject to change, correction, updating. contact
All information and formatting © J Spitz who is responsible for content. Always check with your local dealer-mechanic. Unauthorized reproduction, copying or use prohibited.
thanks for visiting. you are here:  v  11.11.12
Research-   Homepage  Subaru-speak? terms   Warranties safety: airbags, child seats
Buy a Subaru- Subaru sales in Seattle  I Current Interest rates, rebates  I Classifieds, Forum  I   Sitemap   I    contact

Updated April 2012
If the car is supposed to have monitors, if it came with monitors,  a tire/wheel dealer is required to install them.
That means either buy monitors or remove them from other wheels and install them.

The National Highway Safety Administration (NHTSA), a division of the U.S. Department of Transportation, recently clarified provision 49 U.S.C. 30122(b) within the Motor Vehicle Safety Act of 2010.
The provision exactly states:
A manufacturer, distributor, dealer, or motor vehicle repair business may not knowingly make inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable motor vehicle safety standard prescribed under this chapter unless the manufacturer, distributor, dealer, or repair business reasonably believes the vehicle or equipment will not be used (except for testing or a similar purpose during maintenance or repair) when the device or element is inoperative.

The NHTSA further clarified this provision in relation to TPMS in a letter to the Tire Industry Association dated November 22, 2011. In this letter the NHTSA presents the following response to a scenario presented by the TIA:
Scenario: If a motorist purchases a set of aftermarket winter tires and wheels and declines to purchase new TPMS sensors, does the service provider violate 49 USC 30122(b) because they would be installing assemblies that knowingly make the system inoperative?
NHTSB response: In this scenario, we assume that the vehicle has functioning TPMS system at the time he or she purchases aftermarket tires and wheels. In that case, a service provider would violate the “make inoperative” prohibition of 49 USC 30122(b) by installing new tires and wheels that do not have a functioning TPMS system. To avoid a “make inoperative” violation, the service provider would need to decline to install the new tires and rims, use the TPMS sensors from the original wheels (if they are compatible), or convince the motorist to purchase new TPMS sensors and ensure that the sensors aer properly integrated with the vehicle’s TPMS system.

TPMS is standard on the following Subarus
All 2008 and newer Outback
2007: all except Basic
2006 LL Bean, VDC, 3.0R sedan
2005 LL Bean, VDC, 3.0R sedan
All 2008 and newer Legacy
2007 GT
2006 GT
All 2008 and newer Foresters
2007 and before: none
all since 2088
All 2008 and newer Imprezas
2007 and before: none
all since 2012 models
all since 2012 model
all since 2006

How it works:

When the car is turned on the warning light on the dashboard will come on for about 2 seconds. This is normal.
If the light flashes (3 seconds off, 1 second on), that indicates a problem with the system. Contact your dealer.

Each sensor has an separate ID code. When the vehicle goes 7-20 mph, a roll switch inside the sensor turns on and the sensor starts to take measurements every 30 seconds, and sends the results about once a minute to a receiver module under the carpet by the drver's door. The sensors are off when there is no motion (or 15 minutes after stopping).

When a low tire (app 26-27psi) is detected a warning light in the dashboard turns on. The warning light turns on, it does not flash.
The light does not indicate which tire is low, so please check all tires.
A blow-out won't show up right away.

When the vehicle stops moving for 15 minutes, the sensor enters 'sleep' or off mode to save battery life.

WHERE? A transmitter with a tire pressure sensor is located inside the each tire's air valve stem. It is designed to detect low pressure only (not high or over-inflated).
The sensor contains a battery. Battery life is 10 years or 100,000 miles. When the battery fails the sensor must be replaced.


Inflating and Adjusting tire pressure
Be sure to let the tires cool. After adjusting the pressure, drive the car at least 20 mph (32 km/h) to start the TPMS. If a light was on due to low pressure and the pressure is now normal, the warning light should go off after driving for a few minutes. When a spare or a wheel is replaced without the original pressure sensor being transferred, the low tire pressure warning light will flash. This indicates the TPMS is unable to monitor all four road  wheels. Contact your dealer as soon as possible for sensor replacement or system resetting. Do not inject any aerosol tire sealant in the tires because it will damage the sensor, do not place metal film or any metal parts under the driver's seat because this may effect the signal from the sensors.

cold temperatures? cold weather may cause the air tire pressure to drop so the warning light comes on.
This is normal and tire pressure should be checked and corrected seasonally.
When checking and adjusting tire pressure inside when it is in cold or winter outside, the difference between the indoor and outdoor temperature is large. This means that in cold air, the tire pressure may drop and the warning light come on. To avoid this, when inside, inflate the tire slightly more considering the difference between inside and outside temperatures. Or use nitrogen which is less sensitive to cold or hot outside temperatures.

Replace a wheel or use the spare? When you replace the wheel or use the spare tire without the original pressure sensor/transmitter being transferred, the low tire pressure warning light will flash. It needs all 4 sensors feeding it information.

Rotation? The system doesn't know which tire is where so there's no problem with rotations. The dashboard warning light only indicates a low tire but not which tire is low so you have to check all 4.

Parking  Try to make sure the tires aren't pressing hard against the curb when you park.

FLAT repair using a can of pressurized tire repair sealant will clog the sensor and it will have to be replaced

To reset drive the car app 5 miles after correcting for low pressure.

Tire Pressure Monitor re-set tool: To reset the system you'll need a small handheld computer. Needs to be re-synced whenever tires or wheels are replaced.
These are available from Subaru at,  or try aftermarket for less money

Nitrogen in tires - Some dealers are offering Nitrogen as an alternative to inflating tires with normal outside air. Nitrogen maintains tire pressure better than normal air which leaks out over time, and is less sensitive to cold outside temperatures. As a result, Nitrogen minimizes the Tire Pressure Monitoring light coming on.
And because it maintains tire pressure better and is less sensitive to hot and cold, nitrogen can improve economy, increase tire life, and might be safer because the tires are less likely to blow-out when driven at high speeds for a long distance, or on hot roads.
Nitrogen has been used by Nascar, Formula One, the Tour de France and the military for years.
Mixing air and nitrogen. Don't put normal air in a tire with nitrogen because you will lose the nitrogen benefit, but it's not dangerous.
The downside to Nitrogen is that you might have to pay for it (but air is free).

wheel and valve images

Watch for this warning light in the instrument panel. 
Steady illumination means a tire is low, it flashes if there's a problem with the system.

Subaru tire pressure monitor sensor
the sensor and valve stem are i piece. 
The sensor goes inside the tire 
this design was used in all models until 2007.

valve stem, Outback
valve stem
new tire montior started in certain 2008 models
this tire monitor started on 2008 models. 
Notice the brass colored threads

replace valve and stem with every tire change
according to


diagram of the wheel & 
sensor/air valve stem
tire monitor sensor
the sensor in the wheel is part of the normal air valve stem that 
goes through the side 

these images © Subaru of America

warning light

this warning light on the dashboard
goes on when the car is started, or when it senses a problem with inflation (steady on), or with the system itself (flashing).
Note: example only, the light might not be in this location on the dashboard.

This unoffical research page is by Joe Spitz for information only not for mechanical repair
contact your dealer or mechanic for any repairs or any technical questions or issues.
Thank you