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Q: auto zone code is P1456 on 1998 Honda Accord

Check engine light came on and the probable cause from auto zone is loose fuel cap..I checked and the light is still probable causes are..vapor canister saturated, failed vent solenoid and failed purge solenoid. I had an alignment done by Amoco two days before my check engine light came on. Amoco also told me that I had 3 cracks in my engine mounts and it would cost approximately $650.00. Could this be contributing to my problem now? Could you tell me approximately how much it cost to be fixed. I had a transmission put in 2 months ago and I have a three year service contract with the dearlership where I bought this cash car. I don't know what to do. Help me.
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Your engine mounts are not related to your check engine light, 99% sure. The info below is hopefully the solution to your check engine light.

Customer Concern: The engine runs, but the Malfunction Indicator Light (MIL) is on and trouble code P1456 is set. This code indicates that the Powertrain Control Module (PCM) detected a leak on the fuel tank side of the Evaporative Emissions (EVAP) system.
Tests/Procedures: 1. To test the EVAP system, scan the Fuel Tank Pressure (FTP) sensor voltage or test it with a Digital Volt Ohmmeter (DVOM). The sensor has a 3-wire connector. It is located by the canister on the bracket under the plastic cover by the canister. The Light Green wire connects to the FTP sensor signal. The voltage should be close to 2.5v with the fuel cap removed and the ignition key turned on.

2. With the fuel cap on, start the engine and allow it to run. The fuel tank should build pressure and voltage should increase to 2.8v or 2.9v if there are no leaks in the fuel tank area or in the fuel cap.

3. After the voltage increases, turn the engine off and verify that the voltage holds (does not decrease). If the voltage starts to decrease, clamp off the hose from the Bypass Solenoid (BS) and the 2-way valve assembly that runs to the charcoal canister, and see if the fuel tank holds pressure.

4. If the fuel tank holds pressure under these conditions, replace the 2-way valve and the BS, and retest.

5. If the leak remains, use a smoke machine to check for the leak in the fuel tank and filler neck areas.
Potential Causes: Defective BS Two-Way Valve
Cracked Evaporative Emission Hose
Malfunctioning Fuel Cap

Tech Tips: This code can set if the fuel cap is left loose or if the BS and 2-way valve leaks. If the valve leaks, it allows the FTP to decrease (into the charcoal canister) and the Powertrain Control Module (PCM) will set this code.
Diagnostic Codes: P1456

Since you have already replaced your fuel cap, from what I've seen it most likely is going to be your Bypass Solenoid & two way valve.

All this code means is that you have a leak in the EVAP system. It does not mean that your car will not run correctly. It's a emmission related code governed by the EPA.

As far as the mounts go, I'm sure the mounts have wear on them. If you are not feeling excessive vibration I believe you could wait to replace each mount one at a time to work it into your budget. If you have anymore questions e-mail me at
Print out the answer and take it to some shops. You must have taken your vehicle for service somewhere. Remmember bypass solenoid and two valve. I can get a price & a part number tommorrow . E-mail me so I don't have to go thru RepairPal.
Thanks for your answer to my questions. Can you give me the approx. cost for the repair?
Hello Backyard Tech,
Thanks for the great answer.
I have the same code (P1456). One additional problem that I can smell gasoline almost every time I stop, turn off (or idle) and get out of my car. Without doing the check that you mentioned earlier, do you think I have a leaking fuel tank? Can one smell gasoline if either the BS and/or 2-way valve is defective? What are your thoughts?
i just finished with a bit of research about code p1456 and fixed my problem on my Honda Accord 1999.This code is strickley related to the two-way-valve not working that is part of your EVAP system for fuel vapor collection.The gas cap is also possibility but usually not the main answer to this code.I recommend you change out the 2-way-valve located at the canister--dealership charged me $77.00 for the part and I installed myself.erased the code then drove a while for the car to get ready for code readings again, then checked it and no codes present.Do not trust the dogs at Amoco,they are robbers.This code is isolated to fuel vapor recovery and has nothing to do with your other new work....that is it to the point....take care kid
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