P0496: EVAP Flow During a Non-Purge Condition

What is P0496?

DTC P0496 (Diagnostic Trouble Code P0496) is defined as “EVAP Flow During a Non Purge Condition.

The P0496 error code means there’s an issue with the purge flow in the Evaporative Emission Control (EVAP) System, or the system is purging fuel vapor when it shouldn’t. 

The EVAP system seals the vehicle’s fuel system to help prevent the fuel vapor from escaping the gas tank and being released into the atmosphere. Instead, the stray fuel vapor is safely captured by the EVAP canister. 

When the EVAP canister purge valve opens, the intake manifold’s vacuum pulls the fuel vapor into the engine for combustion. The amount of fuel vapor sent to the engine depends on the air that enters the EVAP system through the intake vacuum. 

When Does the P0496 Error Code Appear?

If the Engine Control Module (ECM) detects an unplanned vacuum in the EVAP system — meaning, a purge flow condition is active when it shouldn’t be — it registers the P0496 trouble code and activates the Check Engine Light. 

Normally, the EVAP system regulates the flow of fuel vapors to the engine through controlled purging. A controlled vacuum helps direct the vapor into the intake manifold at the right time. 

However, when a malfunction occurs (such as a stuck purge valve or a loose gas cap), it can cause an unplanned vacuum in the system. This unplanned vacuum may result in excessive fuel vapor being drawn into the intake manifold, causing an overly rich air-fuel mixture.         

NOTE: This code can appear on the OBD II scanner for any vehicle; however, it’s more common in GM & GMC vehicles (Chevy, Pontiac, Cadillac, etc.). For Asian cars (Mazda, Kia, Honda, Hyundai, etc.), the P0496 code stands for “EVAP System High Purge Flow,” which is the same as “EVAP Flow During a Non Purge Condition.”

Common Symptoms

There can be some difficulty in identifying code P0496 since there aren’t many obvious signs. 

Still, you should look out for these symptoms:

• Illuminated Check Engine Light: A blinking check engine light is the most noticeable indicator of car trouble, including an evaporative emission system high purge flow issue.

• Engine issues: A build-up of fuel vapor in the engine could cause starting troubles, rough idling, or other performance problems.

• High fuel consumption: An issue with the EVAP system’s flow control can lead to fuel vapor escaping, causing the ECM to adjust its performance. This may impact fuel efficiency, potentially leading to faster fuel depletion due to evaporation.

• Catalytic converter damage: The engine running rich will lead to excess and incomplete fuel combustion. This unburned fuel can ignite in the exhaust system, which may damage or clog the catalytic converter over time.

P0496 Code Causes

The EVAP system consists of several parts, including:

• Gas tank
• Gas cap
• Charcoal canister (EVAP canister or vapor canister)
• EVAP vent valve (vent solenoid)
• EVAP purge valve (purge valve solenoid)
• EVAP hose (vacuum line)

If any of these parts malfunction, it’ll trigger the code P0496. Common causes include:

• Loose or damaged gas cap
• Faulty EVAP purge valve leading to a high purge flow
• Open purge valve due to carbon deposit build-up
• Failed EVAP pressure sensor (fuel tank pressure sensor)
• Leaking EVAP system hose
• Faulty purge flow sensor
• Leaking or blocked EVAP canister
• Faulty electrical connectors or weak connections
• Short circuit in the sensor wiring

How Serious Is Code P0496, and Can I Still Drive With It?

While it’s not a serious condition, it’s highly recommended to get your vehicle checked out with the help of a mechanic. 

Since this OBD II code triggers the Check Engine Light (CEL), it should be resolved immediately. This way, you won’t overlook any major engine problem, such as a faulty timing belt, malfunctioning oxygen sensor, etc., that could also activate the CEL.

You can still drive with a DTC P0496 for a short period. However, prolonged driving can lead to:

• Catalytic converter damage
• Engine damage
• Low fuel economy
• Increased fuel wastage
• Higher vehicle emissions 

If not handled with care, these problems can cost a lot of money in the long run.

Additionally, in states like California, New York, Massachusetts, and Nevada, a car with a P0496 error code will likely not pass a smog check. As a result, you may be fined or have difficulty renewing your car’s registration.

Diagnosis & Repairs

Since the EVAP system is one of the most difficult systems to access, a high purge flow problem isn’t a DIY fix and requires a lot of care. 

Here’s how a mechanic will perform a proper diagnosis and fix it (step-by-step):

1. Scan the engine light code with the OBD II scanner and turn it off. Then, run the vehicle and scan the code for a second time in order to verify the issue.

2. Check if the gas cap is tightened properly or has any cracks or signs of damage. If it’s loose or damaged, tighten or replace it.

3. Look for EVAP system leaks using a smoke machine. Repair or replace the canister purge solenoid and vent valve solenoid if there’s an engine vacuum leak from those components.

4. Remove the purge valve and vent solenoid valve and apply voltage (around 12 V) to its electrical connectors. If there’s no click when the valve opens, replace the respective valve.

5. Examine the purge valve for signs of charcoal deposits caused by a faulty charcoal canister. If necessary, repair or replace the vapor canister.

6. Check the vent valve in the EVAP system for blockages or debris and clean the component.

7. Inspect the wiring and every electrical connector in the EVAP system (including the EVAP pressure sensor signal wiring) and repair any damaged electrical connector or wire. 

If everything works fine, they’ll test the fuel pressure sensor in order to see if the fuel tank pressure is within the optimal range specified in the manufacturer’s manual. Replace the fuel tank pressure sensor with a new part if it’s malfunctioning.

Once these repairs are done, the mechanic will re-scan the code with the scan tool to ensure the issues have been resolved.

Repair Costs

Depending on their labor rate, a mechanic could charge between $75 and $170 for a diagnosis. After determining the faulty component, they’ll give you an approximate service cost. 

Here’s how much money you’ll have to spend on repairs or a new part:

• Gas cap: $30-$100
• EVAP line (vacuum line): $50-$100
• Electrical connections: $50-$1000
• EVAP purge volume control valve (purge valve): $150-$300
• Canister purge solenoid: $150-$420
• EVAP canister (charcoal canister): $200-$500
• EVAP pressure sensor (fuel pressure sensor): $265-$380