Subaru Tribeca. FUEL tank pressure low diagnosis

The Subaru Tribeca can receive the OBD II generic code P0452.  It means that your Tribeca’s EVAP system has detected low fuel tank pressure.

The fuel vapors are sent from the tank to the intake to be burned.  The system generates P0452 if the pressure gets too low.

When P0452 is not the sole code you experience, don't consider it a breakdown danger. It can usually be fixed with a new fuel cap.

A bad gas cap is often the cause of P0452

Signs

P0452 will not usually be associated with any visible symptoms. Tribeca will continue running fine.

Below are some common symptoms of this code.

• Check engine light (obviously)
• A smell of fuel indicates that there is a leak in the fuel tank or loose fuel cap.
• A hissing sound is an indication of a vacuum leak

Subaru Tribeca: P0452 Causes

These are the most common reasons for P0452 in Subaru Tribeca.

• Gas cap loose
• Low fuel tank pressure sensor, or wiring
• Canisters clogged with charcoal
• Vacuum leak
• Failure to purge the solenoid of EVAP

Subaru Tribeca P0452 Diagnostic Procedure

Here’s a solid order of diagnosis when dealing with P0452 in your Tribeca:

1. You can also check for additional codes

Skip to next section if P0452 is your only trouble code.  If it is not, cross referencing the other code’s causes with the common causes of P0452 can really help you eliminate some possibilities.

2. The Gas Cap

P0452 indicates that your Tribeca’s fuel tank pressure sensor has detected that the pressure in the fuel tank is too low.  The code can be caused by gas caps that are not tightly sealed or not making good seals.

Take off the fuel cap.  You should pay attention to how the rubber ring fits into the fuel inlet.  It is possible to replace P0452 if it has become dryrotted or is damaged.

OBDII codes can remain in your system even after you have fixed the problem.  If you believe that the fuel cap was loose, or you changed it, you’ll need to clear the code with a code scanner and see if it comes back or not.

Make sure there is nothing blocking the fuel inlet.  If it has gunk built up or mud on it, you’ll need to use a wet rag or some WD-40 to clean it off.

If it does come back, we’ll need to move on to the next step.

3. Take fuel pressure measurements

P0452 diagnosis can be difficult, if not for the simple task of checking your gas cap.

A mechanic would use a professional OBDII scanner to check the fuel tank pressure readings from your Tribeca’s fuel tank to see if there is vacuum in the tank.

If it doesn’t look right, the wiring to the fuel pressure sensor would need to be inspected.  

If that doesn’t help anything, the tank pressure sensor itself would need to be replaced.

If everything looks fine, they’d move on to checking the EVAP system.

4. EVAP System Questions

Failures in the EVAP can result in P0452.  Here’s how a good mechanic would go about diagnosing it.  This video is worth watching if this is something you want to tackle yourself.

An Often Mistaken Diagnostic With P0452

When diagnosing P0452, a common mistake is not to check the gas cap before doing so.  

Or, they’ll keep going on with the diagnostic process after addressing the fuel cap because they did not clear their trouble codes.

After you have tightened the cap, start your Tribeca and drive it for awhile to check if the code is clear before proceeding with the diagnosis.

Subaru Tribeca P0452 Conclusion

Bad gas caps are more common than you might think.  It is possible to diagnose P0452 if the gas cap is in good condition.