Check engine light P1456 code?

Hi efreshman,

Hope the following helps.

DTC P1456 '02-04 MODELS: 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

NOTE: If DTC P0461 is stored at the same time as DTC P1456, troubleshoot P0461 first, then recheck for DTC P1456.

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 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 gas. If possible, to assist in leak detection, add 1 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
1. Check the fuel fill cap. It must say "If not tightened 3 clicks check engine light may come on."
Is the correct fuel fill cap installed and properly tightened?
YES: Go to step 2.
NO: Replace or tighten the cap.

2. Check the fuel fill cap seal. Is the fuel fill cap seal missing or damaged?
YES: Replace the fuel fill cap (gray or black colored cap).
NO: The fuel fill cap is OK. Go to step 3.

EVAP Canister Purge Valve Test
1. Disconnect the vacuum hose from the EVAP canister purge valve (A), and connect a vacuum pump to the hose.
2. Turn the ignition switch ON (II).
3. Apply vacuum to the hose. Does the valve hold vacuum?
YES: The EVAP canister purge valve is OK. Go to step 1.
NO: Go to step 4.
4. Turn the ignition switch OFF.
5. Disconnect the EVAP canister purge valve 2P connector.
6. Check for continuity between EVAP canister purge valve 2P connector terminal No. 2 and body ground.

Is there continuity?
YES: Go to step 7.
NO: Replace the EVAP canister purge valve.
7. Disconnect PCM connector A (32P).
8. Check for continuity between EVAP canister purge valve 2P connector terminal No. 2 and body ground.
Is there continuity?
YES: Repair short in the wire between the EVAP canister purge valve and the PCM (A6).
NO: Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING PURPOSE ). If the symptom/indication goes away, replace the original PCM.

EVAP Bypass Solenoid Valve Test
1. Disconnect both vacuum hoses from the EVAP two way valve (A), and connect a vacuum pump to the canister port on the two way valve.
2. Turn the bypass solenoid valve on with the HDS, or connect PCM connector terminal A3 to body ground with a jumper wire.
3. Turn the ignition switch ON (II).
4. Apply vacuum to the hose. Does the valve hold vacuum?
YES: Go to step 5.
NO: Go to step 10.
5. Turn the ignition switch OFF.
6. Disconnect the EVAP bypass solenoid valve 2P connector.
7. Check for continuity between EVAP bypass solenoid valve 2P connector terminal No. 2 and body ground.
Is there continuity?
YES: Go to step 8.
NO: Repair open in the wire between the EVAP bypass solenoid valve and the PCM (A3).
8. Turn the ignition switch ON (II).
9. Measure voltage between EVAP bypass solenoid valve 2P connector terminal No. 1 and body ground.
Is there battery voltage?
YES: Replace the EVAP bypass solenoid valve (A) and the O-rings (B).
NO: Repair open in the wire between the EVAP bypass solenoid valve and No. 6 ECU (PCM) CRUISE CONTROL (15A) fuse.
10. Plug the upper port (A) of the EVAP two way valve.
11. While monitoring the FTP sensor voltage with the HDS, or while measuring the voltage between PCM connector terminals A29 and C18, slowly pump the vacuum pump until the voltage drops to about 1.5 V.
Does the voltage drop to 1.5 V and hold for at least 20 seconds?
YES: The EVAP bypass solenoid valve/EVAP two way valve is OK. Go to step 1.
NO: Repair leakage from the EVAP bypass solenoid valve, EVAP two way valve, FTP sensor, or O-rings.

EVAP Canister Vent Shut Valve Test
1. Disconnect the vacuum hose from the EVAP canister filter (A), and connect a vacuum pump to the hose.
2. Turn the ignition switch ON (II).
3. Apply vacuum to the hose with 5 strokes of the pump. Does the valve hold vacuum? YES: Go to step 4. NO: The EVAP canister vent shut valve is OK. Go to step 1.
4. Turn the ignition switch OFF.
5. Disconnect the EVAP canister vent valve 2P connector.
6. Check for continuity between EVAP canister vent shut valve 2P connector terminal No. 2 and body ground.
Is there continuity?
YES: Go to step 7.
NO: Replace the EVAP canister vent shut valve (A) and O-ring (B).
7. Disconnect PCM connector A (32P).
8. Check for continuity between EVAP canister vent shut valve 2P connector terminal No. 2 and body ground.
Is there continuity?
YES: Repair short in the wire between the EVAP canister vent shut valve and the PCM (A4).
NO: Substitute a known-good PCM and recheck (see HOW TO SUBSTITUTE THE PCM FOR TESTING PURPOSE ). If the symptom/indication goes away, replace the original PCM.

Vacuum Hoses and Connections Test
1. Do the fuel tank vapor control valve test (see Fuel Tank Vapor Control Valve Test ).
Is the fuel tank vapor control valve OK?
YES: Go to step 2.
NO: Replace the fuel tank vapor control valve.
2. Tighten the fuel cap 3 "clicks", then monitor the fuel tank pressure readings with the HDS.
3. Start the engine. Let the engine idle for 5 minutes.
4. Check the FTP sensor readings.
Is the reading above 0.5 kPa (0.16 in. Hg, 4 mmHg) pressure or below - 0.5 kPa (0.16 in. Hg, 4 mmHg) vacuum?
YES: Substitute a known-good PCM and retest (see HOW TO SUBSTITUTE THE PCM FOR TESTING PURPOSE ). If the symptom/indication goes away, replace the original PCM.
NO: Check these parts for leaks:
Fuel tank (A)
Fuel fill cap (B)
Fuel fill pipe (C)
Fuel tank vapor control valve (D)
Fuel tank vapor recirculation valve (E)
Fuel tank vapor recirculation tube (F)
Fuel tank vapor signal tube (G)
Fuel tank vapor vent tube (H)
EVAP two way valve (I)
FTP sensor (J)
Repair or replace any leaking parts.