Experimented with Consent Mode v2 and noticed a sudden drop in traffic in GA4?

You’re not alone!

ConsentMode processes user data based on their preferences, which can naturally lead to fewer visible events. But if the drop seems way steeper than expected, it’s time to check if everything is set up correctly. Don’t worry — it’s easier than you think!

Consent Mode v2 is a tool designed to comply with GDPR while allowing flexibility in how data is processed. When a user denies consent, GA4 models the data—essentially filling in gaps using algorithms. However, if something’s off in your setup, you might end up with far more “missing” data than necessary.

How can you check?

1. Open your browser’s developer console and look for GA4 requests (they usually start with /collect).
2. In the Payload of any request, find the gcs parameter.

What does the gcs value mean?
• G100 – No consent. Data is not collected for either analytics_storage or ads_storage.
• G110 – Consent only for ads_storage. Data flows to GoogleAds, but analytics relies on aggregated data.
• G101 – Consent only for analytics_storage. Data is collected for GA4 but not shared with Google Ads.
• G111 – Full consent. Data is collected and used for both Google \Analytics and Google Ads.

If you expect users to give consent (or if consent isn’t required), the gcs value shouldn’t be G100. If it is, your Consent Mode settings might need some attention.

Possible reasons for issues:

• You or your developers might have forgotten to remove old code that applies default consent settings. For example, an outdated cookie banner could be setting denied by default.
• Consent Mode wasn’t configured properly in the first place.

How to fix it?

Update your cookie banner code and Consent Mode settings to ensure they accurately reflect user preferences. This will reduce the number of events subject to modeling and improve data accuracy.

Pro tip:

Use Google Tag Manager’s preview mode to test how Consent Mode works on your site. It’s a quick way to identify and resolve issues before they affect your data.

If you work with GA4 to BigQuery exports, be sure to check out my SQL cheat sheet.