What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to all vehicles from 1996 onwards (Ford, Honda, Mazda, Mercedes, VW, etc.). Although generic, specific repair steps may vary by make/model.
When I see that a P0497 code has been stored, I know that the Powertrain Control Module (PCM) has detected a low flow condition in the Evaporative Emission (EVAP) purge system.
Designed to capture fuel vapors (from the fuel tank) before they escape into the atmosphere, the EVAP system uses a sealed canister to store excess vapors until the engine is ready to burn them. Fuel vapors are routed to the canister (often called the charcoal canister) via a specially designed valve and a network of metal tubes and rubber hoses. The pressure that builds up when fuel is stored causes the vapors to escape into the tubes and eventually into the canister. The canister contains a charcoal element that absorbs the fuel vapors for release at the appropriate time.
The purge control solenoid is activated when the PCM determines that the engine is in a condition to efficiently burn the EVAP fuel vapors. An EVAP pressure sensor is used to monitor the effectiveness of the EVAP system.
The P0497 code is related to the EVAP purge valve. The purge control solenoid/valve is typically located in the engine compartment. A constant intake vacuum supply hose (from the engine intake manifold) is attached to one opening on the purge control valve, with a second line connected to the only other opening. In most cases, a constant battery voltage supply is present at one terminal of the purge control valve, and the PCM provides a ground pulse when driving conditions are optimal. This allows the valve to open and admit vacuum to reach the canister. When vacuum reaches the canister, ambient air is drawn through the charcoal element, releasing the stored fuel vapors. The engine vacuum draws the fuel vapors into the intake manifold where they are burned with conventional fuel.
In some systems, if there is not a sufficient change in intake manifold air pressure or exhaust oxygen content when the purge control solenoid/valve is opened, a P0497 will be stored and a malfunction indicator lamp may soon 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 does not drop sufficiently when the purge control valve is opened, a code will be stored and the malfunction indicator lamp will soon illuminate.
Symptoms
and Severity
This is an emissions-related code. While it may slightly reduce fuel efficiency, there is no inherent danger. Symptoms of a P0497 code may include:
Slightly decreased fuel efficiency
Noise from a vacuum leak in the area under the hood
Poor engine idle quality
In most cases, no symptoms will be apparent
Causes
Possible causes for setting this code are:
Faulty EVAP pressure sensor
Faulty EVAP purge solenoid/valve
Restricted EVAP canister element
Short circuit or open circuit (wiring or connector) for the EVAP purge control solenoid/valve
Cracked, pinched, or collapsed vacuum lines/hoses
Diagnostic and Repair Procedures
A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your problem may be a known issue with a known fix published by the manufacturer and can save you time and money during diagnosis.
A suitable diagnostic scanner, a digital volt/ohmmeter, a manufacturer’s service manual (or equivalent), and a smoke machine will help diagnose the P0497 code.
I usually start my diagnosis with a visual inspection of all system wiring and connectors, as well as vacuum lines and hoses. Repair or replace any damaged wiring and/or connectors as needed.
The EVAP system consists of a network of long vacuum lines and metal tubes, which can be a chore in itself. If you have access to a smoke machine, it can make this process much easier. Keep in mind that most of these vacuum circuits will have no vacuum unless the purge control solenoid/valve is activated. Repair or replace faulty vacuum lines and hoses as needed.
If charcoal is found in the vacuum lines, immediately suspect a faulty canister. Compromised charcoal elements usually cannot be replaced individually and will likely require a complete canister replacement. Connect the scanner to the diagnostic connector and retrieve all stored codes and freeze frame data. Write all of this down so you can refer back to it later. Clear all codes and test drive the vehicle. Remember that resetting this type of code may take several drive cycles. If it resets, continue 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 for vacuum flow with the engine running when the purge control solenoid is activated.
If the solenoid does not open when activated, check the system voltage and ground signals against the manufacturer’s specifications. If voltage and ground signals are present, suspect a faulty solenoid. Test the purge control solenoid (with the DVOM) using the service manual as a guide. If voltage and ground signals are absent, disconnect the 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 meet the manufacturer’s specifications, suspect a faulty PCM or a PCM programming error.
Additional Diagnostic Notes:
Engines in poor condition may not provide sufficient vacuum for EVAP purge operation
A loose or missing fuel cap will not cause this code to be stored
To effectively use the smoke machine, remove the vacuum lines from the canister and plug them before applying smoke