If your website has a cookie banner, consent mode v2 is quietly deciding how much of your Google Ads and GA4 data you get to keep. Set up well, it lets Google measure and model the visitors who say no. Set up badly, or not at all, you lose conversions you never knew you had, remarketing audiences shrink, and your campaigns optimise on a thinner slice of reality than they should.
The trouble is that most broken setups look fine. The banner appears, the tags fire, and nothing tells you the consent signals are wrong. Here is what consent mode actually does and how to check yours.
What consent mode does
Consent mode is how your cookie banner talks to Google’s tags. When someone lands on your site, the banner records their choice, and consent mode passes that choice to Google Ads, GA4 and Floodlight, so each tag knows what it is allowed to do.
The original version had two signals: ad_storage (can advertising cookies be set) and analytics_storage (can analytics cookies be set). Version 2 added two more: ad_user_data (can user data be sent to Google for advertising) and ad_personalization (can the data be used for personalised advertising such as remarketing).
Since March 2024, Google has expected these signals for European traffic if you want to keep using audience features such as remarketing, and its consent policy also covers visitors from the UK. If the two newer signals are missing, Google treats the data more conservatively, and features you rely on can stop working without any obvious error.
Basic or advanced: the choice that matters most
There are two ways to run consent mode, and the difference has a big effect on your data.
- Basic mode blocks Google’s tags completely until the visitor accepts. If they decline, Google receives nothing at all about that visit.
- Advanced mode loads the tags straight away with consent denied. They send cookieless pings that carry no identifiers, and when the visitor accepts, the tags update and behave normally.
Advanced mode is what makes conversion modelling possible. Google uses those cookieless pings to estimate the conversions it could not observe directly, so the totals in Google Ads and GA4 sit closer to what actually happened. Modelling needs a minimum amount of traffic before it switches on, so smaller sites may not see it straight away, but basic mode rules it out entirely.
Which mode is right is partly a legal question for your business, not only a technical one. What matters is that you choose deliberately, rather than ending up with whatever a plugin did by default.
Five checks you can run yourself
- The default is set before anything fires. Consent mode needs a default state, normally denied for UK and European visitors, set before any Google tag loads. If the default is set too late, the first hits of a visit go out with no consent signal at all.
- All four signals are present. Open Google Tag Assistant, load your site and look at the consent tab for a Google tag. You should see
ad_storage,analytics_storage,ad_user_dataandad_personalization. If the last two are missing, you are still on version 1. - Accepting actually updates consent. Click accept on your banner and check Tag Assistant again. Each signal should change from denied to granted. If nothing changes, the banner and consent mode are not connected.
- Declining is respected. Clear your cookies, decline, and browse a few pages. Advertising and analytics cookies should not appear in your browser’s storage. If they do, you have a compliance problem as well as a data problem.
- Google Ads shows no consent warnings. In Google Ads, check the diagnostics for your conversion actions and the status of your audience lists. Google flags missing consent signals there, often long before anyone notices the effect on results.
The common ways it goes wrong
Most of the broken setups we audit fall into a handful of patterns. A cookie plugin is installed but never connected to Google Tag Manager, so the banner works and the tags ignore it. Tags are hard-coded in the theme as well as in Tag Manager, so one copy respects consent and the other does not. The banner was set up before version 2 and has never been updated, so the two newer signals are never sent. Or the default is granted for everyone, which keeps the numbers high but is not what your visitors chose.
None of these show up as an error in Google Ads. They show up as remarketing lists that never grow, conversions that drop for no obvious reason, and campaigns that seem to perform worse each month.
Where to go from here
Consent mode is now part of the measurement layer, as much as GA4 or your conversion tags, and it deserves the same care. If you are not sure what your site is sending, it takes an hour or two to check properly and the answer usually explains numbers that have been puzzling you for months. It is also the first thing to fix before enhanced conversions, which depend on the same signals.
If you would rather have it checked for you, this is part of our conversion tracking and GA4 work, and it sits underneath everything we do on Google Ads management. Get in touch and we will tell you what your site is sending today.