Well it was -4 this morning when I got into work and just before shutting off the engine I noticed the check engine light had come on. It was deja vu from about one year ago when the temp was below zero and on came the check engine light. It spent 3 days in the shop with everyone scratching their heads why it was on. Ended up being something with a purge pump. Now I have to admit after the new parts and tank, my DEF usage dropped dramatically (like 80%). I thought these trucks were designed to operate in cold temps, but I'm guessing they haven't got all the issues resolved with DEF in cold weather. I can't afford to miss work this time so it will have to sit all day, and hopefully it clears itself after it gets home and sits in the garage overnight and warms up.

 

It was warmer at lunch, about 8 degrees. Starts right up, idle is fine before and after warming up. Drove around for 20 minutes at lunch and it runs fine, but the check engine light is still on.

 

Went to the dealer after work and no surprise it was the same error code from a year ago. i told him it would be one he didn't recognize but he didn't believe me, but I enjoyed the confused look and his reply, never seen this one before.

I have a good idea what is causing it, and I believe it is weather related and I bet (weather permitting) I can recreate this over and over again. It took some convincing but I got him to clear the code as I was convinced there was nothing wrong or broken, that it was just the computer confused about what was happening.

I asked if he wanted to make a record of this happening with my vehicle and he said no which makes no sense. I just couldn't see GM spending all that money under warranty to fix something a second time (and third and so forth) that likely isn't broken. I'm sure the cost of parts and labor for replacing the entire DEF tank is not cheap!!!

We all know that a true failure would regenerate the error. It's been driven home, and to work this morning without an error, but the temp is above the threshold of where it will generate the error code.

If someone from GM would like to review this further, they are more than welcome to contact me.