|Trouble Code||Fault Location||Probable Cause|
|P1456||Evaporative emission (EVAP) canister purge system (fuel tank system) – leak detected||Hose, fuel tank/pressure sensor, fuel filler cap, EVAP valve/bypass solenoid, EVAP two way valve, EVAP canister/vent valve|
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What Does Code P1456 Mean?
OBD II fault code P1456 is a manufacturer specific code that is defined by carmaker Honda as “Evaporative Emissions (EVAP) Control System Leakage (Fuel Tank System)”, and is set on these applications when the PCM (Powertrain Control Module) detects a leak in the EVAP (Evaporative Emissions) control system.
The purpose of the EVAP system on all applications is to trap, and contain fuel vapors within the system until engine-operating conditions are such that the trapped vapors can be transported to the engine to be combusted as part of the air/fuel mixture. While design specifics vary, EVAP systems generally consist of the fuel filler cap, the fuel tank, various flow and pressure sensors, purge and vent valves and their associated solenoids that are electronically controlled, a charcoal canister, various pipes, hoses and vacuum lines, and electrical wiring.
When the EVAP system is not in purge mode, both the vent and purge valves are closed, which has the effect of sealing the fuel system off from the atmosphere. As the fuel generates vapors, the vapors are absorbed by the activated charcoal in the charcoal canister, until the vapor pressure approaches a predefined limit. When this happens in a fully functional system, the ECU opens both the purge valve and the vent valve to allow engine vacuum to draw the accumulated vapors into the engine. Note that the purpose of opening the vent valve is to allow atmospheric pressure to assist in “pushing” the collected vapors from the charcoal canister.
However, since a fully functional EVAP system is a legal requirement in most jurisdictions, car manufacturers have developed various strategies to detect leaks in the system. One such strategy is to open the purge valve while keeping the vent valve closed while engine vacuum partially evacuates the system. Based on how fast the vacuum decays after the purge valve is closed, the PCM can calculate the size of the leak.
Another strategy involves using a dedicated air pump to pressurize the system (while keeping all valves closed) to a predefined maximum pressure. Based on how fast the pressure drops after the pump is deactivated, the PCM can also calculate the size of the leak. Another strategy involves the Ideal Gas Law, which states that the temperature of a given volume of gas (fuel vapor, in this case) will decrease by a predictable amount when the pressure of the vapor decreases. Based on the change in the vapor’s temperature, the PCM can calculate the size of the leak.
While the presence of a leak in the EVAP system will generally not affect drivability, a leak will cause code P1456 to be stored and a warning light to be illuminated. The application may also not pass a compulsory emissions test.
Where is the P1456 sensor located?
The image above shows a schematic diagram of the EVAP system on most Honda applications. Note that although all labeled parts are common sites for leaks, the area in the red oval indicates the most common sites for leaks that relate to code P1456 on the following Honda models-
- 2002-04 CRV
- 2002-03 S2000
- 2002-04 Insight
What are the common causes of code P1456?
The most common cause of code P1456 on the Honda models listed above is a defect in the fuel filler cap that prevents the filler cap from seating properly. However, since this defect has been rectified in the intervening years, other common causes of this code could include the following-
- Perforated, or otherwise damaged hoses. Note that EVAP hoses on Honda applications are not known for their high quality, which means that almost any hose on these applications can develop leaks at almost any point
- Defective EVAP vent valve
- Defective vapor recirculation valve
- Defective fuel tank pressure sensor