Subaru Forester: P0453: Too high Fuel Tank Pressure Sensor/Switch

Subaru Forester's evaporative emissions controller (EVAP) uses a system that moves fuel vapors between the fuel filler neck of the tank and the fuel tank to send them to the engine for burning.  If the fuel tank pressure is too high P0453The check engine light turns on when a, is thrown.

The Forester won't fail to function if P0453 is the only code of concern.  The EVAP system controls the movement of fuel vapor.  The EVAP system's ability to move fuel vapor has no bearing on your engine's performance.  We don't endorse ignoring this code.

The EVAP isn't always functioning.  It uses a  valve to open and close the system to release fuel vapor into the engine to be burned off.

It is the fuel tank pressure sensor that detects excessive pressure.  This sensor measures air pressure within the tank. It does not measure fuel pressure.  If it does so, then P0453 will be thrown.  The fuel tank pressure sensor, also known as the fuel pump pressure sensor, is usually located on top of your gas tank or fuel pump.

The opposite of this code is P0452, which is thrown whenever the system pressure is too low.

P0453 Symptoms:  Subaru Forester

This code is usually not associated with any symptoms.  The check engine light will illuminate (that’s why you’re here).

You may only notice the fuel smell.  If your EVAP system doesn't properly remove fuel vapor it will seek other escape routes.

There are many causes

These are some of the most common reasons for P0453.

• Charcoal canister Clogged vent valve
• Fuel tank pressure sensor damaged (sensor or wiring).
• Fuel tank damaged
• PCM/ECM (highly unlikely)

Diagnose P0453 with the Subaru Forester

Diagnosing P0453 in your Forester can be challenging if you don’t have a scan tool that is capable of reading the fuel pressure sensor data or capable of commanding the vent valve to open and close.

Here are some things you can do at home

• If you happen to notice the sound of air escaping when you take your Forester’s gas cap off, that is a telltale sign that the vent valve is bad, or the charcoal canister is bad(it’s pressure leaving the gas tank).  Once you have driven for some time, turn off the gas cap and go somewhere else.  It’s hard to notice the sound when you’re at a noisy gas station.
• You should check the wiring for the fuel tank pressure sensor to see if there are any frayed wires.  If it isn’t then the only way to really diagnose it is with a professional mechanic’s scanner.  It can be difficult to look at the tank without dropping it.

What a Mechanical Engineer Will Do

• To determine if the sensor detects vacuum, a mechanic will take data from the fuel pressure sensor.
• The vent valve will be opened and closed by them.  You can also hear the engine running depending on your vehicle's year.

A mechanic can inspect the wiring leading to the fuel pressure sensor if the fuel tank pressure is not within the specifications.  A mechanic will inspect the wiring leading to the fuel pressure sensor and replace it if that is found.

The charcoal canister must be replaced if the vent valve turns on and the pressure sensor works fine.  If the vent valve doesn’t come on, it will need replacement in order to clear P0453.

If all appears to be in order, it could indicate that the PCM may not work properly.

Subaru Forester: P0453 Conclusion

That’s pretty much it.  While there are only a couple of common things that’ll cause P0453, there it can be tough to diagnose it without the right equipment.  It’s not going to leave you stranded on the side of the road either.  Good luck fixing your Forester!