Prior to September 2007, some car makers offered an optional tire pressure monitoring system that kept close tabs on a vehicle’s tire pressure and alerted the driver of any sharp decrease. Initially, this system had two types: direct and indirect. The direct system had a sensor inside each tire to monitor each tire individually. The indirect system worked through the vehicle’s antilock brake system, measuring the speed of each wheel and comparing them with each other. If one tire rotated slower than the other, a light illuminated on the dashboard, alerting the driver of the low pressure. All cars manufactured after September 2007, such as the 2008 Impreza, came standard with the direct TPMS in accordance to new federal regulations. Resetting the 2008 Impreza’s tire pressure light is not much more difficult than adding air to the tires.
Unscrew the cap from each of the valve stems — the rubber stems protruding from each rim. Place the valve stem caps in a secure location.
Press the tire pressure gauge onto the top of the valve stem — the brass part — and hold it firm to gain an accurate reading of the tire pressure. Make note of the pressure. Ideally, you should check your tire pressure prior to driving and in a temperature of 60 degrees F or above — cold weather lowers the pressure inside the tire at a rate of 1 psi per 10 degrees F.
Repeat Step 3 on all four tires.
Compare the pressures noted in Steps 2 and 3 with the correct tire pressure for the 2008 Impreza — 33 psi in the front tires and 32 psi in the rear tires — to determine what tires require more air. Please note: only tires lower than the recommended psi by more than 2 psi require air.
Park the Impreza near an air hose connecting to a compressed air source and turn the vehicle off.
Press the air chuck onto the top of the valve stem — in the same manner you did with the pressure gauge — to start the flow of air into the tire. To estimate the amount of time to hold the air chuck onto the tire, a good rule-of-thumb is every 3 to 5 seconds increases tire pressure by 1 psi.
Remove the air chuck and check the pressure in the tire by following Step 3.
Repeat Steps 7 and 8 until the air pressure is within 2 psi of recommended tire pressure of 33 psi on the front and 32 psi on the rear.
Repeat Steps 6 through 8 to adjust any other tires that are low on air pressure.
Screw the valve cover caps back onto all four valve stems.
Start the Impreza and drive to an open road with little or no traffic.
Accelerate to a speed of at least 20 mph.
Observe as the “Tire Pressure” light on the instrument cluster turns off after about 2 minutes.
