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Error Code P0496 is defined as EVAP (evaporative emission) Flow During A Non-Purge Condition, a problem usually caused by faults in the wiring, EVAP valve, or a mechanical issue.
This error code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
As with other systems inside a vehicle’s engine, the EVAP (Evaporative system) is controlled by the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes). And with this, it comes with a number of self-checks to make sure that it is performing properly, with the goal of reducing emissions before letting it escape to the atmosphere.
In a case of a fault, the PCM will set an EVAP-related trouble code and trigger the Check Engine light indicator. One of the most common problems in the EVAP system occurs when the PCM determines a vacuum when there should be any, which can be caused by different reasons, such as stuck open purge valve. In this case, the Error Code P0496 is set. This also happens when the vacuum in the EVAP system is more than the predetermined value in a set amount of time.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. In many cases, it doesn’t come with noticeable symptoms. In some cases, however, symptoms can include:
- Hard starting or crank condition
- Engine running rich (may not be detected, but can cause damage long-term)
There can be a lot of possible causes for this code to appear, such as:
- Defective purge or vent solenoid/valve
- Plugged EVAP canister
- Damaged EVAP / fuel pressure sensor
- Problem in electrical connection
- Short electrical circuit condition (usually happens in Hyundai and Isuzu)
- Defective canister purge valve
- Blocked vapor canister
- Defective vent solenoid
- Leaking EVAP system hose (Hyundai)
How to Check
Technicians diagnose this code using an advanced scan tool, with ignition on, engine off. They will seal the EVAP system using the Seal/Purge function. Then they will watch the fuel tank pressure sensor reading after turning the purge off. If the pressure value is higher than the predetermined range set by the manufacturer, then the EVAP canister purge solenoid valve is at fault.
Without the advanced scan tool, the technician can check by disconnecting the vacuum line at the purge valve going back to the charcoal canister. They will unplug the electrical connector on the purge valve, start the engine, and then put their finger on the valve where they disconnect the line. If there is vacuum felt, then the purge valve solenoid is faulty and must be replaced.
Alternately, they can also remove the purge solenoid valve and blow into it. This will normally be closed, so if air goes through, then it’s faulty and must be replaced.
If the purge valve is in good condition, the problem could be intermittent, or there is an issue with the fuel tank pressure sensor. To test the latter, an advanced scan tool is used to monitor the tank pressure with the gas cap removed. If the sensor shows vacuum without the gas cap, then the problem is in the fuel tank pressure sensor.
How to Fix
The most common fix for this code is to replace the purge solenoid valve. Of course, a thorough diagnosis is required before you replace any parts.
When replacing the EVAP canister purge solenoid valve, make sure you get to the specific model. Refer to the repair guide for the proper specifications.
A short-to-power condition can also cause this error code, which usually happens due to poor installation or repair, and using aftermarket accessories or misrouting the harness after a repair.