TLDR: Consent Mode v2 is Google’s framework for managing user consent signals across your tags and it’s non-negotiable if you run Google Ads to users in the EU. Without it, you risk GDPR breaches and lose visibility into a significant chunk of your conversions.
What you need before you start
Before you touch a single tag, make sure these three things are in place. Consent Mode isn’t just a Google Ads setting, it’s a whole-website setup that also affects your GA4 data.
A compatible Consent Management Platform (CMP)
Consent Mode v2 requires a CMP that actively passes consent signals to Google. Popular options include OneTrust and Cookiebot, both have solid market share and strong integration with Google’s framework. You can check whether your current CMP is compatible via Google’s published list, which is regularly maintained.
Access to Google Tag Manager
You’ll need someone comfortable in GTM. This isn’t a job for a non-technical marketer, you’ll want a developer or a tagging specialist involved. Your GTM container also needs to be properly linked to both your Google Ads account and your GA4 property.
Your Google Ads and GA4 accounts linked to GTM
This is almost always the case, but worth confirming before you start. If they’re not linked, the signals won’t flow through correctly.
Step 1: Configure your CMP to pass Consent Mode v2 signals
Your CMP is the starting point. It needs to be set up to pass two specific consent signals to Google:
- ad_storage – controls whether cookies can be used for advertising purposes
- analytics_storage – controls whether cookies can be used for analytics
Most major CMPs have a built-in integration for Consent Mode v2. Check your CMP’s documentation for the specific setup steps, they vary by platform, but the principle is the same: the CMP fires the relevant consent signals before any other tags load.
This sequencing is critical. Consent must be granted (or denied) before you collect any data. If your consent tag fires after your tracking tags, you’re already picking up data from users who haven’t had the chance to consent, which defeats the entire purpose of the framework and opens you up to compliance risk.
Step 2: Update your Google Tag Manager container
Once your CMP is passing consent signals, you need to configure GTM to receive and act on them. Google has made this deliberately straightforward, they want you to implement it, so the walkthrough inside GTM is clear. At a high level, you’ll need to:
- Enable consent overview in your GTM container settings
- Set consent initialisation triggers so your CMP fires first in the tag sequence
- Update your Google tags (Google Ads conversion tracking, GA4) to require the relevant consent types before firing
Again, tag sequencing is everything here. Your consent tag needs to be first in the firing order. When a user declines consent, that signal should automatically prevent the rest of the data-gathering sequence from running.
If you’re not confident in GTM, get your developer involved. This is 50% marketing platform knowledge, 50% someone who’s comfortable with tags and firing rules.
Step 3: Verify your setup with Tag Assistant
Google’s Tag Assistant (built into GTM’s preview mode) lets you fire test events and check that your consent signals are being sent correctly.
When you open the Tag Assistant output, the first thing to find is the consent default event. This should be set to denied, meaning that before a user has interacted with the cookie banner, consent is withheld by default. That’s the correct starting state.
What happens next depends on whether a cookie banner is shown:
- If no cookie banner appears, it means the browser has already stored a previous consent decision (accepted or declined). In this case, you should see a second consent event labelled ‘update’ reflecting that stored choice.
- If the cookie banner is shown, the ‘update’ event will not fire until the user makes a decision on the banner. That’s expected behaviour, the update only triggers once consent is actively granted or denied.
Beyond that, here’s what else to confirm in Tag Assistant:
- Consent signals firing before any other tags
- ad_storage and analytics_storage showing the correct granted/denied status based on simulated user choices
- Your Google Ads and GA4 tags only firing when consent is granted
If something looks off in Tag Assistant, stop here and fix it before moving on. Getting the verification right at this stage saves a lot of troubleshooting later.
Step 4: Check your Consent Mode status in Google Ads
Once you’ve verified in GTM, head into Google Ads and check your conversion goals. Go to your conversions page and click into each individual conversion action. If there are consent-related issues, Google Ads will surface a warning against that conversion. Click into the warning for more detail, it’ll tell you exactly what the problem is.
This is a basic hygiene check that’s easy to miss. People tend not to inspect each conversion individually on a regular basis, but after a setup change like this, it’s essential. Don’t skip it.
Step 5: Confirm modelled conversions are active
Here’s the thing about Consent Mode v2: even with a perfect setup, some users will decline consent. That’s expected. In the EU, cookie acceptance rates typically sit between 25% and 35%, which means roughly 65% of conversions won’t be directly tracked.
That’s where modelled conversions come in. Google uses the consented data it does have, combined with Enhanced Conversions (which uses first-party data like email addresses and phone numbers, not cookies), to model the conversions it can’t directly observe.
To confirm modelling is working:
- In Google Ads, compare last-click attribution against data-driven attribution (DDA). You should see a difference, which reflects the modelled layer.
- In GA4, look at what’s being recorded directly versus what GA4 models for untracked sessions. This would depend on whether you are using DDA (Data –driven attribution) and whether google signals is toggled on.
- Check that modelled conversions are actually appearing in your reports, not just that the feature is enabled, but that it’s producing data.
Enhanced Conversions should be running alongside Consent Mode v2. It’s not a replacement, it’s complementary. Together, they give you the most complete picture possible within a consented framework.
How to know if it’s working and what to do if it’s not
Once everything’s live, monitor across multiple platforms. The person who set it up in GTM won’t always be the same person running Google Ads day-to-day, so make sure both sides know what to look for.
Signs it’s working
- Modelled conversions are appearing in Google Ads and GA4
- No consent-related warnings on your conversion actions
- Smart bidding is stable, no unexpected drops in conversion volume
- Last-click vs DDA shows the expected variance
Signs something’s gone wrong
- Your smart bidding strategy suddenly constricts, if you’ve recently switched to Consent Mode v2 and your bid strategy is losing 20–30% of its conversion data, it will start to tighten. Smart bidding takes about a week to react to a data drop, so keep a close eye on performance in the days after go-live.
- Consent warnings appear on your conversions page in Google Ads
- GA4 shows a significant jump in unassigned or untracked sessions
- No modelled conversions are appearing at all
If you see smart bidding constrict after switching over, that’s a strong signal your modelled conversions aren’t flowing through. Go back to your Tag Assistant verification, check your conversion diagnostics in Google Ads, and confirm Enhanced Conversions is active. This shouldn’t happen if you’ve done all the previous checks, but if you’ve missed a step, that’s usually where it shows up.
The bottom line: check Google Ads, check GA4, and have your technical person check GTM. Between those three, you’ll catch any issues quickly.
Why this matters for your brand
Two reasons: First, compliance. GDPR fines are real, and using customer data without proper consent isn’t just a legal risk, it’s a brand reputation risk. If your privacy policy says one thing and your tags are doing another, you’re exposed.
Second, data quality. Consent Mode v2, paired with Enhanced Conversions and modelled data, gives you the most accurate picture of performance that’s possible within a privacy-first framework. Without it, you’re optimising on incomplete data, and making budget decisions you can’t fully stand behind. Want to know how complete your measurement really is? Just ASK BOSCO®.
