Technical Description of OBD-II Trouble Code
Low Purge Flow in the Evaporative Emission System
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured in 1996 or later (such as Ford, Honda, Mazda, Mercedes, VW, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
When I encounter a stored code P0497, it indicates that the powertrain control module (PCM) has detected a low flow condition in the evaporative emissions (EVAP) purge system.
The EVAP system is designed to capture fuel vapors from the fuel tank before they are released into the atmosphere. It utilizes a closed reservoir, usually called a canister, to store excessive vapors until the engine is ready to burn them. Fuel vapors are directed to the canister through a specially designed valve and a network of metal tubes and rubber hoses. The pressure created when fuel is stored causes the vapors to vent into the tubes and eventually the canister. The canister contains a charcoal element that absorbs fuel vapors and releases them at the appropriate time.
The purge control solenoid is activated by the PCM when it determines that the engine is in a state to efficiently burn the EVAP fuel vapors. An EVAP pressure sensor is used to monitor the efficiency of the EVAP system.
The P0497 code is related to the EVAP purge valve, which is usually located in the engine bay. One opening of the purge control valve is connected to a constant intake vacuum supply hose from the engine intake manifold, while the other opening is connected to a second line. In most cases, there is a constant supply of battery voltage at one terminal of the purge control valve, and the PCM provides a ground pulse when optimal drivability conditions are met. This allows the valve to open and intake vacuum to reach the canister. When vacuum reaches the canister, ambient air is drawn through the charcoal element, releasing the fuel vapors that have been stored. The engine vacuum then draws the fuel vapors into the intake manifold, where they are burned alongside conventional fuel.
In some systems, if there is not a sufficient change in manifold air pressure or exhaust oxygen content when the purge control solenoid/valve is opened, a P0497 code will be stored and the service engine soon lamp may illuminate. Other systems use an EVAP pressure sensor to monitor and control the operation of the purge and vent control solenoids. In this type of system, if the EVAP pressure fails to drop sufficiently when the purge control valve is opened, a code will be stored and the service engine soon lamp may illuminate.
Symptoms & Severity
This code is related to emissions. While it may slightly reduce fuel efficiency, there is no inherent danger. Symptoms of a P0497 code may include:
Causes
Possible causes for this code to be set are:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
To diagnose code P0497, you will need a suitable diagnostic scanner, a digital volt/ohmmeter, a manufacturer’s service manual (or equivalent), and a smoke machine.
I have a habit of beginning my diagnosis by visually inspecting all system wiring and connectors, as well as vacuum lines and hoses. Repair or replace any damaged wiring and/or connectors as necessary.
The EVAP system consists of a network of long vacuum lines and metal tubing, which can be a challenging task to inspect. If you have access to a smoke machine, it can simplify this process. Keep in mind that most of these vacuum circuits will have no vacuum present unless the purge control solenoid/valve is activated. Repair or replace any defective vacuum lines and hoses as needed.
If charcoal is found in the vacuum lines, suspect a defective canister. Compromised charcoal elements usually cannot be replaced individually and will likely require complete canister replacement. Connect the scanner to the diagnostic connector and retrieve all stored codes and freeze frame data. Write down all this information for future reference. Clear all codes and test drive the vehicle. Keep in mind that it may take several ignition cycles for this type of code to be reset. If it resets, continue with your diagnosis.
Consult the service manual for specific system specifications and test the operation of the EVAP purge solenoid/valve. Use the scanner to activate the purge control solenoid and physically check vacuum flow with the engine running and the purge control solenoid activated.
If the solenoid fails to open when activated, check the system voltage and ground signals according to the manufacturer’s specifications. If voltage and ground signals are present, suspect a defective solenoid. Test the purge control solenoid using the DVOM (digital volt/ohmmeter) with the guidance of the service manual. If voltage and ground signals are absent, disconnect system controllers and test the system circuits with the DVOM. Repair or replace any open or shorted circuits as necessary.
If all system circuits and components comply with the manufacturer’s specifications, suspect a defective PCM or a PCM programming error.
Additional diagnostic notes:
