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DTC P1456: Evaporative Emission Control System Leak Detected (Fuel Tank System): Notes

WARNING: This page is about a different car, the 2003 Acura RSX. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Evaporative Emission (EVAP) 2-way valve is part of EVAP bypass solenoid valve.
  1. Check fuel filler cap (Filler cap must say "If not tightened 3 clicks check engine light may come on"). Check fuel filler cap seal. Repair or replace as necessary and ensure cap is tightened at least three clicks. If filler cap, seal and pipe are okay, disconnect both vacuum hoses from EVAP 2-way valve. Connect vacuum pump to canister port on 2-way valve. See Fig 1 . Turn EVAP bypass solenoid valve on with scan tool, or connect fused jumper wire between ground and White ECM/PCM 31-pin "E" harness connector terminal No. 20 (Blue/Red wire). Turn ignition switch on. Apply vacuum with vacuum pump. If EVAP 2-way valve holds vacuum, go to next step. If valve does not hold vacuum, go to step  4 .
    Fig 1: Testing EVAP 2-Way Valve
    G00110174Courtesy of AMERICAN HONDA MOTOR CO., INC.
  2. Turn ignition switch off. Disconnect EVAP bypass solenoid valve 2-pin harness connector. Check for continuity between ground and EVAP bypass solenoid valve 2-pin harness connector terminal No. 2 (Blue/Red wire). If continuity is present, go to next step. If continuity is not present, repair open in Blue/Red wire between EVAP bypass solenoid valve 2-pin harness connector terminal No. 2 and White ECM/PCM 31-pin "E" harness connector terminal No. 20.
  3. Turn ignition switch on. Measure voltage between ground and EVAP bypass solenoid valve 2-pin harness connector terminal No. 1 (Black/Orange wire). If battery voltage is present, replace EVAP 2-way/bypass solenoid valve. If battery voltage is not present, repair open in Black/Orange wire between EVAP bypass solenoid valve and No. 4 ACG fuse (10-amp).
  4. Plug fuel tank port of EVAP 2-way valve. See Fig 2 . While monitoring Fuel Tank Pressure (FTP) sensor voltage with scan tool or measuring voltage between White ECM/PCM 31-pin "E" harness connector terminals No. 4 (Pink wire) and 14 (Light Green wire), slowly apply vacuum until voltage drops to 1.5 volts. If voltage drops to 1.5 volts and holds for at least 20 seconds, EVAP 2-way/bypass solenoid valve is okay. Go to next step. If voltage does not drop to 1.5 and hold for at least 20 seconds, repair leak from EVAP 2-way/bypass solenoid valve or FTP sensor.
    Fig 2: Identifying & Plugging Fuel Tank Port On 2-Way Valve
    G00110179Courtesy of AMERICAN HONDA MOTOR CO., INC.
  5. Perform Fuel Tank Vapor Control (FTVC) valve test. See FUEL TANK VAPOR CONTROL VALVE (FLOAT TEST)  and FUEL TANK VAPOR CONTROL VALVE (VALVE TEST)  . If FTVC valve is okay, go to next step. If FTVC valve if faulty, replace FTVC valve.
  6. Tighten fuel filler cap 3 clicks and monitor FTP sensor readings with scan tool. Start engine and allow to idle for 5 minutes. Check FTP sensor readings. If FTP sensor reading is more than 0.16 Hg (0.5 kPa), update ECM/PCM or substitute with known-good ECM/PCM. If symptom or indication goes away, replace original ECM/PCM. If FTP sensor readings are not as specified, check following components for leaks:
    • Fuel tank
    • Fuel filler cap
    • Fuel filler pipe
    • Fuel tank vapor control valve
    • Fuel tank vapor recirculation valve
    • Fuel tank vapor recirculation tube
    • Fuel tank vapor signal tube
    • Fuel tank vapor control vent tube
    • FTP sensor

    Repair or replace components as necessary.

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