Q: Code P0496.

asked by on

I have a 2010 GMC Acadia. I'm getting the code p0496. I have replaced the fuel rail sensor, purge valve and the gas tank pressure sensor. My engine light is still on. What else could it be?

My car has 148000 miles.
My car has an automatic transmission.

This may be obvious, but have you cleared the code with the scanner? If so, disregard that first sentence. Codes will not clear immediately after the repair. With an emissions system code, there is also a drive cycle to be considered as well. The code can be cleared but the drive cycle tests must pass based on the computer system self tests. So the code will clear after a repair if the system is fixed, but it will take a few drive cycles that meet some exacting circumstances to clear the code. If the code is cleared and the light comes back on, then the repair was not successful. Again, this paragraph maybe redundant, but not everyone knows all this.

Moving on to what you can do next. There are two solenoids, so you will need to make sure you have replaced the correct one. There is a canister purge solenoid and a canister vent solenoid. This codes states that one of these two solenoids is open. Either due to an electrical problem or a mechanical problem. The PCM (powertrain control module) routes vacuum from the motor to the fuel tank and puts the fuel tank into a low pressure condition. This is done in various different ways depending on what the PCM is testing. This is a part of a drive cycle and drive cycle test happen only under specific circumstances. But we are focused on both solenoids being closed as this code indicates the PCM was unable to stop the vacuum from being applied to the fuel tank.

The best way to test this system is with a scanner and many times a smoke machine. Also needed will be the ability to get under the car and information as to how the emissions system is programmed. This will include wiring diagrams. Without this, all of us are guessing as to why the PCM is still seeing a low pressure AKA vacuum in the fuel tank. The first components to suspect, one of which you have already replaced are the vent and purge solenoids. Beyond them, you will be chasing a bad electrical connection that are typical in all systems. In this case I would be inspecting all connectors and harnesses involved in the evap system.

If you require help with this system, I recommend the following inspection to help you out. Check engine light

Good luck!

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Vibration or is shaking feeling in seat and steering wheel.

I would take the vehicle to another shop and ask them to check the lateral run-out of both the tires and the wheels. Lateral run-out is the side to side motion. Wheels that are slightly bent or out of round,...

Q: I have a 2004 Mercedes Benz ML350.

Hi there. Check the brakes and the wheel speed sensors to see if the are damaged or worn causing the ESP light to come on. A worn brake pad can cause the ESP light to come on as the wheel...

Q: Battery runs down in two days if the engine is not running. The alternator has 14 volts.

Hi there. It seems that there is a parasitic load on your vehicle's battery when the vehicle is sitting and not running. Check the battery for a voltage and see if the charge is 12.6 volts. If the battery is...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...