If your Google Ads conversions have dropped, or Smart Bidding seems to be guessing instead of optimizing, the cause is sometimes sitting in your cookie banner, not your campaign settings.
The mechanism: Consent Mode v2 isn't optional anymore
Since March 2024, Google requires Consent Mode v2 for any site running Google Ads or Analytics in the EEA/UK. Without it correctly configured, two things happen:
- Conversion tracking gets modeled, not measured, for every visitor who hasn't consented — Google estimates the missing data statistically instead of counting it directly. The more visitors decline (or the banner is broken and nobody's asked at all), the more of your reported conversions are modeled guesses.
- Smart Bidding strategies (Target CPA, Maximize Conversions) train on that modeled data. Feed it bad signal — because consent defaults are misconfigured, or because the CMP never actually calls
gtag('consent', 'update', ...)on a real "Accept" click — and your bidding strategy optimizes toward the wrong audience without any error message telling you why.
This is a quiet failure mode: campaigns keep running, clicks keep costing money, and the dashboard shows real numbers — just the wrong ones.
The specific misconfiguration we see most often
A CMP that integrates with Consent Mode v2 is supposed to call gtag('consent', 'default', {...}) with everything set to denied before any tag fires, then call gtag('consent', 'update', {...}) the moment a visitor actually accepts. The common failure: the default call either never runs, runs with the wrong values, or runs after Google Tag Manager has already fired other tags — meaning the "denied" state existed only in theory, never in practice. Visually, nothing looks wrong. The banner shows up, the buttons work, the site looks finished.
Landing-page/ad-language mismatches make it worse
A German-language ad pointing traffic at an English-only landing page is its own problem (trust, bounce rate), but it compounds a Consent Mode issue: a visitor who bounces in 3 seconds never gets to the consent decision at all, which Google Ads reads as "this audience doesn't convert" rather than "this audience never saw a usable page."
How to check your own setup
Open your browser's DevTools Network tab, reload the page without accepting anything, and look for Google Ads/Analytics requests firing anyway. If you see them, Consent Mode's default state isn't actually blocking anything — it's decorative.
Bannerproof checks this automatically, including whether your CMP's Consent Mode default signal is actually set to denied before any tracker fires — not just whether the banner is visually present. The first scan is free and takes under a minute.
This article is informational, not legal advice. Bannerproof is an independent scanning tool, not a law firm or a data protection authority — see our Terms of Service for details.