Consent Mode is Google’s way of telling its tags what a visitor has agreed to. Your cookie banner records the choice, and Consent Mode passes it to Google Analytics 4, Google Ads and other Google tags, which then decide whether to set cookies and what data to send.
How Consent Mode works
It runs on a small set of signals, each either granted or denied:
- analytics_storage Whether analytics cookies may be used;
- ad_storage Whether advertising cookies may be used;
- ad_user_data Whether data about the visitor may be sent to Google for advertising;
- ad_personalization (Google’s American spelling): whether that data may be used for personalised ads and remarketing.
The last two arrived with Consent Mode v2. On page load, a default state is set before any Google tag fires, and for UK visitors that default should be denied. When the visitor makes a choice in your consent management platform, an update command switches the relevant signals to granted. In Google Tag Manager the default runs on the Consent Initialization trigger, and most CMPs supply a template that handles both steps.
There are two ways to run it. In Basic Consent Mode, Google tags do not load at all until the visitor consents, so nothing is sent for people who refuse. In Advanced Consent Mode, tags load straight away in a restricted state and send cookieless pings for visitors who have not consented. Google uses those pings to estimate the behaviour and conversions it cannot observe. Google Ads still produces some modelled conversions in Basic mode, from a more general model, but GA4 behavioural modelling needs Advanced.
Why it matters
From March 2024, Google began requiring valid consent signals for traffic from the UK and the European Economic Area. Without v2 signals, features such as remarketing audiences and personalised ads stop working for that traffic, and conversion measurement in Google Ads becomes less complete. If you advertise on Google to UK customers, Consent Mode is part of a working account rather than an optional extra.
What it does not do is make a site lawful. Consent Mode only carries a signal. The banner itself still has to meet PECR and UK GDPR standards: no non-essential cookies before consent, a Reject option as easy to use as Accept, and clear information about each purpose. It also has no effect on other companies’ tags. The Meta Pixel, LinkedIn Insight Tag, TikTok pixel or Hotjar need blocking by your CMP, or by triggers in GTM, until the visitor agrees. Microsoft Advertising has its own consent signal for its UET tag.
Advanced mode needs a decision of its own. The cookieless pings still send some information to Google before consent, such as a timestamp, the page and browser details. Whether you are comfortable with that, and how you describe it in your privacy notice, is a judgement for your business and, where the stakes are high, for your legal adviser.
Common mistakes
- Default set too late. If the default command loads after a Google tag has fired, that tag behaves as though consent was granted.
- Only the older signals passed. A banner that updates ad_storage but not the two v2 signals leaves Google Ads treating UK traffic as unconsented for advertising.
- Granted by default. Some set-ups default to granted and rely on the banner to switch things off, which reverses the legal position.
- Assuming it blocks every tag. It controls Google tags only.
- Expecting modelling on a small site. Google applies traffic thresholds before it models, and many small business sites never reach them.
How to act on it
Open your site with Tag Assistant connected, load a page without touching the banner, and look at the consent state: all four signals should show denied before any Google tag fires. Accept, and confirm they update. Reject in a fresh session, and confirm they stay denied. Then check that non-Google tags do not fire in either test until you accept.
GA4 and Google Ads both report whether consent signals are arriving, in their admin and diagnostics screens; the exact location moves as Google updates the interfaces, so search their help pages for consent mode status if you cannot find it. Choose Basic or Advanced deliberately, write the choice down, and make sure your privacy notice matches it. Setting and testing Consent Mode before any budget is spent is part of my PPC management service.