DTC Advanced Diagnostics: P0456: General Description

Courtesy of HONDA, U.S.A., INC.

Courtesy of HONDA, U.S.A., INC.

The evaporative emission (EVAP) leak detection system uses an engine off natural vacuum (EONV) method. The EONV method detects leakage from the change in fuel tank pressure via the fuel tank pressure (FTP) sensor with the engine off.

Here is an overview of the malfunction detection for the EONV method:

Judgment 1: Judgment of detection of 0.09 inch leak as normal operation

Judgment 2: Judgment of detection of 0.02 inch leak as normal operation

Judgment 3: Detection of 0.02 inch leak

<Judgments 1, 2, and 3 happen at the same time.>

Judgment 1: 

After the engine has stopped, the powertrain control module (PCM) monitors the variation of the FTP sensor output to detect "no 0.09 inch leak" depending on the variation of the pressure inside the fuel tank.

• If the variation of the pressure is a specified value or more before first monitoring duration has passed, it is identified as normal and the diagnosis completes.
• If the variation of the pressure is less than a specified value for a specified duration after first monitoring duration has passed, it is identified as a "0.09 inch leak" and the diagnosis completes. (P0455)
• If the variation of the pressure is a specified value or more before maximum monitoring duration has passed, it is defined as "no 0.09 inch leak", the judgment of detection of a 0.09 inch leak is completed, and it goes to 0.02 inch leak monitor.

Judgment 2: 

After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect "no 0.02 inch leak" depending on the variation corresponding to the change rate of pressure decrease gradient inside the fuel tank.

• If a "0.02 inch leak" is detected, it is identified as a malfunction; the diagnosis is completed. (P0456)
• If "no 0.02 inch leak" is detected, it is identified as normal; the diagnosis is completed.
• If the pressure is not atmospheric pressure or less when the detection is completed, Judgment 2 is suspended and determines the judgment by result of Judgment 3.

Judgment 3: 

After the engine has stopped, the PCM monitors the variation of the FTP sensor output to detect "no 0.02 inch leak" depending on the variation corresponding to the change rate of pressure increase gradient inside the fuel tank.

• If "no leakage" is detected and Judgment 2 is suspended, it is identified as normal; the diagnosis is completed.
• If a "0.02 inch leak" is detected and Judgment 2 is suspended, it is identified as a malfunction; the diagnosis is completed.
• If "no leakage" is detected and the pressure inside the fuel tank reaches to a specified value, it is identified as normal without waiting the result of Judgment 2; the diagnosis is completed.
• If a "0.02 inch leak" is detected and the pressure inside the fuel tank reaches to a specified value, it is identified as a malfunction without waiting the result of Judgment 2; the diagnosis is completed.
• If the pressure of the fuel tank does not increase to a specified value or more within a specified duration, the judgment is suspended.

Monitor Execution, Sequence, Duration, DTC Type 

Execution	Once per driving cycle
Sequence	P0455 is judged as OK
Duration	At least 10 minutes but not more than 36 minutes 40 seconds
DTC Type	Two drive cycles, MIL on