Most teams treat cookie consent as a front end problem. Add a banner, get a click, done. For Google Ads and GA4, that is only half the job.
The four parameters Google Ads reads
Google's Consent Mode API expects four specific signals from your site: ad_storage, analytics_storage, ad_user_data, and ad_personalization. Each one controls a different piece of tag behaviour. ad_storage governs advertising cookies. analytics_storage governs GA4 cookie usage. The two newer parameters, ad_user_data and ad_personalization, were added in November 2023 and specifically gate whether Google Ads can use data for personalised ads and Enhanced Conversions.
What happens when the signal doesn't arrive
If you run Consent Mode without setting these correctly, here is what happens per Google's own developer documentation: tags load with defaults, usually denied, and wait for a gtag('consent', 'update', ...) call. If that call never fires, or fires with the wrong values, Google Ads and Analytics behave exactly as if the visitor denied everything, even if your banner shows they accepted.
Region-specific defaults
Google also lets you scope defaults by region, using ISO 3166-2 codes, so you can set analytics_storage to denied for EEA visitors while granting it elsewhere by default. This matters if you serve a mixed audience and do not want to block measurement in regions with no consent requirement.
Consent Mode vs IAB TCF
There is a second path: the IAB Transparency and Consent Framework (TCF). If your CMP uses TCF, Google reads the TC string instead. Google explicitly recommends against running both Consent Mode and TCF at the same time, since conflicting signals get resolved in favour of the more restrictive one, which can silently suppress data you thought you were collecting.
Where Seers fits in
For teams doing server-side tagging or managing multiple domains, the practical fix is auditing which signal path is active on each property before assuming your setup works. Seers is a Google-certified CMP (Gold tier) that maps all four parameters to your tags automatically, applies region-specific defaults out of the box, and lets you switch between Consent Mode and TCF instead of running both by accident.
Full technical walkthrough in the Google consent manager setup guide.