Andy, I haven't worked on a problem like yours, but if you don't mind doing a little work yourself, I think this is a perfect situation where the source of your leak could be easily found with the use of a simple smoke machine that you build yourself for next to nothing. See this video for more:
Home Made Smoke Machine

 

Interesting and thanks! I like trying things like this so I may give it a shot. I just wonder if I can find it myself if it's something I'll be able to repair. And, still a bit surprised I even have this issue on a 2017 Cadillac with 27K miles on it.

 

Hello, I own a 2017 XTS with only 27,000 miles on it. The check engine light came on the other day so I went to Auto Zone and used their diagnostic scanner to check the code. It showed PO442 (1/1) Permanent (EVAP) System Small Leak Detected. Has anyone here had an evaporative emission system leak on their Cadillac? I'm pretty surprised by this because of the relative newness of and low mileage on the car. Any thoughts or past experience by someone dealing with the same issue would be appreciated, thanks!

Why not use your warranty? The dealer is far more qualified than Auto Zone.

 

Could be as simple as a loose or bad gas cap. But since XTS does'nt a have a gas cap there must be another arrangement that needs to close it off. I had a gas tank fuel pump/ sending unit rubber seal go bad once. That took the smoke machine to find. You can only put 1 PSI or so to the gas tank and system or there will be issues.

 

Thanks all. I just bought the car in December and actually wasn't 100% certain this would be covered under warranty. Past that, I also wondered if anyone else had experienced this because as I originally posted it surprised me on a relatively newer car with so low miles. Thanks again.

 

Andy, I think that it would not only be covered under the 50,000/5 year bumper-to-bumper warranty, it would also be covered under the emissions system warranty, which is quite a bit longer, like 80,000 miles or something like that.

 

Yup - emissions warranties exceed the regular old B to B vehicle warranty. EVAP is a Federal emissions mandate for controlling excess fuel vapor emissions to atmosphere.

You might check and see if the EVAP purge test port cap is in place. Probably a small green plastic tire cap on the purge line near the solenoid at the throttlebody. The other possibility is a leak at the fuel fill pipe connectors. System pressure/vacuum is monitored by the fuel tank pressure sensor.

 

Submariner, thanks for the info about the fuel tank pressure sensor. I always wondered how the EVAP system knew that a leak was detected. Now I know. Is that sensor located along with the other fuel pump/level sending unit components that insert at the top of the tank?

 

Depends on the vehicle make, model, year. The "factory service manual" for the vehicle will have schematics and descriptions of the various EVAP systems, parts, and their operation.

Depending on operating conditions the tank vent is either open to atmosphere or shunted to a charcoal canister for vapor storage. During steady state driving conditions over about 30 mph the purge valve opens, the canister vent to atmosphere opens, and the intake vacuum draws fresh air through the charcoal canister, purging the stored fuel vapor for burning with the normal intake fuel/air mixture - it doesn't take long - maybe 30 seconds to a minute. The purge is done when the small extra air added to the intake mixture will not affect driveability.

Some years of the Escalade/GMC/Chevy truck series had real troubles with the charcoal retainer screens in the canister breaking and allowing charcoal granules into the vent/purge lines. Charcoal granules got sucked/blown throughout the entire pressure/vacuum system, causing all sorts of fuel fill and trouble code problems.

 

Once again, that was a very helpful description of the EVAP system operation, Submariner. I can see how the canister gets purged of fuel vapor without the driver even aware of it once the car gets up to speed. Now it makes me wonder how the purging operation gets shut down once the fuel vapor has been purged from the canister. Is it just based on time, or is there some kind of sensor that detects the amount of fuel vapor present?

 

Time, intake airflow (power demand), engine speed, vehicle speed over time, other factors. The system is actually pretty "smart".

Bottom line: It's a SWAG - Scientific Wild Ass Guess.