Error Code P1456 is described as a Evaporative Emission Control System Leak. This means there’s a leak problem in the EVAP (Evaporative Emission Control System), particularly on the tank side, and the engine’s computer has detected the issue.


Error Code P1456 means there’s a fuel vapor leak problem or lack of purge flow in the in the engine’s EVAP control system, and the computer of the vehicle has detected the leak. As with other codes that start with P1xxx, this error code however, is a manufacturer specific code. Thus, the diagnosis and repair for this error code may vary from one brand of vehicle to another.

The general idea however is that, the problem is caused by a leak in EVAP system of the vehicle, specifically in the fuel tank, which can be a result of missing cap, loose or use of wrong fuel cap, leaks in fuel tank, hoses or tubes.

The job of the EVAP system is to keep fuel vapor from escaping the fuel system. Fuel vapors passes through the routed hoses straight to a charcoal canister for storage. Later, when the engine starts and runs a purge control valve will open and allow the intake vacuum to drain off the fuel vapors into the engine.

The EVAP captures any raw fuel that evaporates from the fuel storage (fuel cap, fuel tank, and filler cap). These captured fuel vapors are sent back to the combustion process by the EVAP system, under precise operating conditions, which is dictated by the speed, load and temperature of the engine.

Unburned drops of raw fuel are harmful for health and the environment as it can cause breathing problems and contribute to smog.

How the PCM Detects the Error Code P1456

What the code actually indicates is that, the vehicle’s EVAP system will not make a significant vacuum when it does its leak test, as monitored by the Fuel Tank Pressure Sensor.

Here’s how the PCM conduct the EVAP leak test.

  1. To conduct the leak test, the vehicle must have been sitting overnight, or at least four hours. This is to bring down the temperature of the engine and make its temperature identical to the outside temperature. There should also be fuel in the tank (around 15% to 85%) to provide a good baseline for test, since diesel and gasoline are both volatile fluids that easily expands and vaporizes from warm temperature.
  2. When the leak test starts, the Vapor Canister Vent Valve will close, keeping any outside air from getting to the EVAP system.
  3. The Purge Valve will open, letting the engine make a vacuum in the EVAP system.
  4. After a specific time interval (around 10 seconds), the Purge Valve will shut off, giving the Fuel Tank Pressure Sensor chance to measure the vacuum level in the system.
  5. Then, a countdown will start to measure the rate of vacuum decay in the system. If the vacuum goes off faster than specific time, or if there’s no vacuum reached after two consecutive tests, the PCM will automatically fail the EVAP system and trigger the P1456 error code to indicate a gross leak.

Common Symptoms

  • Check Engine light is on
  • Noticeable fuel vapor odor caused by leak
  • No drivability and vehicle or engine performance symptoms

Possible Causes

  • Missing or loosely placed gas cap
  • Use of non-conforming gas cap (not original brand)
  • Damaged fuel tank or filler neck
  • Faulty fuel tank pressure sensor
  • Damage or leaks in the EVAP system (torn or punctured hoses)
  • Damages on Evaporative vent valve or purge valve
  • Damaged carbon canister

How to check

When diagnosing the vehicle for this error code, it is imperative that the EVAP system is completely sealed, along with the most common components that may have leaks, such as the gas cap, vent valve, purge valve, hoses and connectors.

First Test – The very first thing you need to inspect is the gas cap. Check whether it is placed right. If it is left open or loosely placed, then close it tight and check whether the ‘Check Engine’ light disappeared after a few drives.

Sometimes, the problem is in the gas cap itself. Take a closer look at your gas cap and look for signs of wear and tear, including the rubber gasket. If you see obvious signs of damage, then it is time to replace them with a new one.

Second Test – If there are no signs of damages in the gas cap, then there might be a leak in the EVAP system. This is where you will need the advance scan tool and other testing equipment, such as the ‘smoke machine.’ The smoke machine detects leaks by pushing smoke through the system. This smoke will exit through holes and leaks, helping you visually detect the leak. Obviously, this is where you may need the help of a professional mechanic, which means you need to take your vehicle to his shop for a thorough diagnosis (such as smoke test) and professional repair.

Your mechanic will run a smoke test along with a scan tool with live data stream feature to the Fuel Tank Pressure Sensor PID. They will also conduct a smoke test on the entire EVAP system, and check for fuel odor.

How to fix

Here are some of the most common ways to repair your vehicle from this Error Code:

  • Remove the gas cap and reinstall it properly and tightly to the filler neck. Clear the codes from the code reader, drive the car for a day, then check it again using the scan tool to see if the error code comes back.
  • Replace the gas cap if necessary.
  • Check the EVAP system for damages, leaks, cuts, and holes on its hoses and tubes. If you notice vacuum noise or smell any fuel vapor, then conduct the necessary repairs.

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