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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8612
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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2002 Diamante: Mitsubishi..Circuit..P0455..Leak..the 02 sensor

Resolved Question:

2002 Diamante Mitsubishi emission code P0155:02 Sensor Heater Circuit Bank 2 Sensor 1 and P0455:Evaporative Emission System Leak Detected (Large Leak). I have changed the 02 sensor but still get the reading to change. Any solutions for these issues?
Submitted: 6 years ago.
Category: Mitsubishi
Expert:  Doug replied 6 years ago.

A few questions here about your problem:

Have you cleared the codes and they have returned, or are you waiting for them to go away on their own and they have not yet?

Which O2 sensor did you replace (describe it's physical location), and what brand sensor was it?

Was anything done regarding the P0455?

Customer: replied 6 years ago.
I have cleared them and they returned. The O2 sensor was located on the pass. side of vechile at the rear upper.
nothing else done for p0455
Expert:  Doug replied 6 years ago.
Okay thanks.

The first problem we have is that the wrong O2 sensor was replaced.
Bank 2 sensor 1 is located on the radiator side of the engine, upper sensor. A good way to identify sides of the V6 engines is by head placement.... "Bank 1" and "Bank 2" refer to which side (or bank) of the engine contains cylinder 1 and cylinder 2. The side or bank of the engine which will always have cylinder 1, is the head that is shifted slightly forward compared to the other head.

In any event. on this vehicle, Bank 1 is the firewall/rear side of the engine, and Bank 2 is the radiator/front side of the engine. So you will need to replace the radiator upper sensor to take care of the P0155.

Now in regards XXXXX XXXXX P0455, this is going to be an unrelated code as far as the O2 sensor goes, and will need to be addressed separately. The code is referencing a vacuum leak in the evaporative system. The first thing I would do is pull your gas cap off and inspect the center of it, make sure there is no large hole there (early caps and aftermarket caps have a tendency to fall apart, dropping the center portion of the cap into the tank).

If the cap looks good, we are going to be dealing with either a major damage to a hose (P0455 is a very large leak), or a stuck open purge or vent solenoid. The most common is a stuck open vent solenoid, these get changed quite often on these cars. The vent solenoid is located on the charcoal canister in the back of the vehicle. Testing is easiest with a proper scan tool but can be checked manually as well. Air will pass through the solenoid at rest, and air will be blocked when energized. The coils fail on these as well as the solenoid will stick; both will prevent it from energizing, preventing it from blocking air flow, allowing a very large leak in the evap system, causing the code to set.
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