Comment # 2 on bug 1037592 from Dominique Leuenberger

How did you get to the conclusion that the cron job is running? Any log files
to support that theory?

I rather suspect that you have a GNOME desktop in front of you and GNOME
Software is installed, which handles the lookup of updates out of the desktop
session - not via the PK cron job.

The command "gsettings get org.gnome.software download-updates" will show if
this feature is enabled

using "gsettings set org.gnome.software download-updates false" it can be
disabled; but note that GNOME will not inform about any pending updates in this
case.