What does it mean?
OBD II fault code P0497 is a generic code that is defined as “Evaporative emission (EVAP) system -low purge flow”, or sometimes as “Evaporative Emission System No Flow during Purge”, depending on the manufacturer, and/or the source consulted. Nonetheless, both definitions have the same basic meaning, which is that code P0497 is set when the PCM (Powertrain Control Module) detects an EVAP (Evaporative Emissions Control) system purge flow rate that is lower than expected.
The purpose of the EVAP system is to capture, contain, and carry fuel vapors to the engine to be combusted before said fuel vapors can escape into the atmosphere to contribute to environmental pollution. To accomplish this, all EVAP systems are sealed by the fuel filer cap, a vent valve that allows ambient air to enter the system to assist in the displacement of fuel vapors to the engine, and a purge valve that allows fuel vapors to flow towards the engine.
While some design specifics vary between manufacturers, the overall design and operation of EVAP systems are similar, in the sense that fuel vapors are collected, stored, and then fed into the engine in a controlled manner when certain conditions demand that the system be purged of vapors, or when purging the system of fuel vapors will not affect engine performance negatively.
With a few exceptions, such as a dedicated leak detection pump on some applications, all EVAP systems consist of the fuel tank, fuel filler cap, a charcoal canister that stores fuel vapors, a vent valve that allows fresh air to enter the canister to help “push” stored fuel vapors from the canister, a purge valve between the canister and the engine that allows fuel vapors to flow into the engine when the valve is opened, various control solenoids, vacuum lines, and pressure and flow sensors.
In practical terms, fuel vapors will remain in the system (stored in the charcoal canister) until a predefined pressure is reached. When this happens, and when conditions allow, the PCM opens the vent valve on or near the charcoal canister to admit fresh air, while at the same time opening the purge valve to allow engine vacuum to “suck” the stored fuel vapors out of the charcoal canister.
In a fully functional system, the PCM determines the amount of fuel vapor to be purged, based on input data from various pressure sensors. The PCM also determines the rate at which the fuel vapors must be purged to prevent negative effects on engine performance, and it does this by comparing current operating conditions such as the engine speed and load, throttle position, and other parameters with the rate at which vapors are being purged, which data the PCM obtains from a flow rate sensor.
By comparing the actual flow rate with the desired flow rate, the PCM can control the opening and closing of the purge valve in such a way that the two flow rate values (actual and desired) agree. Thus, when the PCM determines that the flow rate required to purge the EVAP system effectively is lower than expected for whatever reason, it will set code P0497, and illuminate a warning light.
Note that on some applications, several fault cycles are required before a warning light is illuminated, while on others, a warning light will be illuminated on the first failure. The image below shows a simplified schematic of a typical EVAP system. Note the two components circled in red; these are the two most common sites of failures that set code P0497, but be aware that other faults, such as kinked or blocked vacuum lines between the purge valve and the engine can also set this code.
Refer to the manual for the application being worked on to locate and identify the various components of the EVAP system on that application before attempting a diagnosis and/or repair of the system to avoid confusion, misdiagnoses, and the unnecessary replacement of parts.