DTC P1456: EVAP Control System Leakage (Fuel Tank System)

NOTE: The fuel system is designed to allow specified maximum vacuum and pressure conditions. Do not deviate from the vacuum and pressure tests as indicated in these procedures. Excessive pressure/vacuum would damage the EVAP components or cause eventual fuel tank failure

Special Tools Required

Vacuum Pump/Gauge, 0-30 in. Hg A973X-041-XXXXX

This is a two-trip code; once cleared, it cannot be reproduced in one trip. Also, certain specific driving and ambient conditions must occur before the ECM/PCM will complete the system checks. Additional test drives may still not meet the specific conditions needed to reproduce the code.

Follow these troubleshooting procedures carefully to ensure the integrity of the system and to confirm the cause of the problem or code.

NOTE: Fresh fuel has a higher volatility that will create greater pressure/vacuum. The optimum condition for testing is fresh fuel and less than a full tank of fuel. If possible, to assist in leak detection, add one gallon of fresh fuel to the tank (as long as it will not fill the tank), just before starting these procedures.

Fuel fill cap check

Check the fuel fill cap. It must be a gray or black OEM cap and be tightened at least 3 "clicks" to properly seal the system.
Is the correct fuel fill cap installed and properly tightened?
1. YES - Go to step 2.
2. NO - Replace or tighten the cap.
Check the fuel fill cap seal.
Is the fuel fill cap seal missing or damaged?
1. YES - Replace the fuel fill cap (gray or black colored cap).
2. NO - The fuel fill cap is OK. Go to step 3.
EVAP Bypass Solenoid Valve Test
Disconnect the vacuum hose from the EVAP two-way valve (A), and connect a vacuum pump to the hose.

Fig 1: Connecting Vacuum Pump To The Hose
Courtesy of AMERICAN HONDA MOTOR CO., INC.
With the Honda PGM Tester in the EVAP test mode, turn on the bypass solenoid, or connect ECM connector terminal A3 to body ground with a jumper wire.

Fig 2: Connecting ECM Connector Terminal A3 To Body Ground With Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Turn the ignition switch ON (II).
Apply vacuum to the hose.
Does the valve hold vacuum?
1. YES - Go to step 7.
2. NO - The EVAP bypass solenoid valve/EVAP two-way valve is OK. Go to step 12.
Turn the ignition switch OFF.
Disconnect the EVAP bypass solenoid valve 2P connector.
Check for continuity between EVAP bypass solenoid valve 2P connector terminal No. 2 and body ground.

Fig 3: Checking Continuity Between EVAP Bypass Solenoid Valve 2P Connector Terminal No. 2 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Go to step 10.
2. NO - Repair open in wire between the EVAP bypass solenoid valve and ECM/PCM (A3).
Turn the ignition switch ON (II)
Measure voltage between EVAP bypass solenoid valve 2P connector terminal No. 1 and body ground.

Fig 4: Measuring Voltage Between EVAP Bypass Solenoid Valve 2P Connector Terminal No. 1 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?
1. YES - Replace the EVAP bypass solenoid valve (A) and the O-rings (B).
2. NO - Repair open in the wire between the EVAP bypass solenoid valve and No. 6 ECU (ECM/PCM) CRUISE CONTROL (15A) fuse.
  
  Fig 5: Replacing EVAP Bypass Solenoid Valve & O-Rings
  Courtesy of AMERICAN HONDA MOTOR CO., INC.
Plug the upper port (A) of the EVAP two-way valve.

Fig 6: Plugging Upper Port Of EVAP Two-Way Valve
Courtesy of AMERICAN HONDA MOTOR CO., INC.
While monitoring the FTP sensor voltage with the Honda PGM Tester, or measuring the voltage between PCM connector terminals A29 and C18, slowly pump vacuum until the voltage drops to approximately 1.5 volts.

Fig 7: Measuring Voltage Between PCM Connector Terminals A29 & C18
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Does the voltage drop to 1.5 V and hold for at least 20 seconds?
1. YES - The EVAP bypass solenoid valve/EVAP two-way valve is OK..
2. NO - Repair leakage from the EVAP bypass solenoid valve, EVAP two-way valve, FTP sensor, or O-rings.