germancarlover89

Could use some help here with this. I have a 2006 4.2L A6. Just got the code about two days after getting gas so naturally I checked the gas cap. Turned it three clicks to make sure it got a good seal but two days later and about 50 miles later, still have the mil. Looked at other people's post and see a lot of info but confusing. Was told by the person at advance auto that when these codes are thrown together it's usually a faulty gas cap. I appreciate the help in advance.

FormulaElement

Are there any other symptoms besides the light? Do you happen to have a VAG-Com by any chance?

There are many places to start, you can buy a new gas cap and start there. I would probably check all of your hoses and make sure they're tight and still in good condition first though.

This response isn't specific to Audi's but could be useful.

P0455-EVAP SYSTEM LARGE LEAK
Theory of Operation

The Evap Purge Monitor tests the integrity of the hoses/tube between the throttle body/intake and the fuel tank. The monitor is a two stage test and runs only after the Evap system passes the small leak test. Stage one is non-intrusive. The Powertrain Control Module (PCM) monitors the purge vapor ratio and the Evaporative System Integrity Monitor (ESIM) Switch closed ratio. If the purge vapor ratio is above a calculated value, the monitor passes. If the ESIM switch closed ratio is greater than calculated value when purge flow is greater than a minimum value, the monitor passes. Stage two is an intrusive test and runs only if stage one does not pass. The PCM commands the purge solenoid to flow at a specified rate to force the purge vapor ratio to update. The ratio is compared to a calibrated specification. If it is less than specified, a one trip failure is recorded. This test can detect if the purge hose is off, obstructed, or the purge valve is not operational.

When Monitored: With the engine running, during a cold start test with the fuel level above 12%, ambient temperature between 4C and 32C (39F and 89F) and the fuel system in closed loop. The test runs when the small leak test is maturing.

Set Condition: The PCM activates the Evap Purge Solenoid to pull the Evap system into a vacuum to close the ESIM switch. Once the ESIM switch is closed, the PCM turns the Evap Purge solenoid off to seal the Evap system. If the ESIM switch reopens before the calibrated amount of time, a large leak error is detected. Two Trip Fault. Three good trips to turn off the MIL.

Possible Causes
EVAP PURGE SOLENOID VACUUM SUPPLY
EVAP PURGE HOSE/TUBE OBSTRUCTION
EVAP SYSTEM LEAK <<< most likely cause
EVAPORATIVE SYSTEM INTEGRITY MONITOR (ESIM) SWITCH

P0456-EVAP SYSTEM SMALL LEAK
When Monitored: With the ignition off, fuel level less than 88%, ambient temperature between 4C and 43C (39F and 109F).
Set Condition: As temperatures change, a vacuum is created in the fuel tank and Evap system. With the Evap system sealed, the Powertrain Control Module (PCM) monitors the ESIM switch. If the ESIM switch does not close within a calibrated time, an error is detected by the PCM. One Trip Fault. Three good trips to turn off the MIL.

Possible Causes
EVAP PURGE SOLENOID VACUUM SUPPLY
EVAP PURGE HOSE/TUBE OBSTRUCTION
EVAP SYSTEM LEAK <<< most likely cause

germancarlover89

I really appreciate the information. You are obviously very knowledgeable. I unfortunately don't have a vag com so I can't troubleshoot that way. I will definitely check for leaks and go from there. Just installed a new gas cap today and will let you know if that does the trick.

raj99

The 2nd thing after buying an Audi or any VAG car, should be a VCDS. It's money well spent and will save you from throwing parts at a problem without any actual data.

germancarlover89

Thanks. I will definitely need to invest in that.

eazy211187

If the gas cap doesn't resolve the issue, check EVAP PURGE SOLENOID.
There's 2 way of knowing that EPS is bad.
1) while the car on you hear pinging sound(like marbles).
2) EPS will be extremely hot.

Also you'll be able to check if there's a vacuum leak as well.

germancarlover89

Ok so I have an update. Took it to the shop. Got a new gas cap (oem) and 50 miles later mil back on. Will check the evap purge solenoid. Where is this located? Thanks!