Consent Mode v2 debugging guide

What this is

Consent Mode v2 debugging is the task of confirming that a page sends the four consent signals — ad_storage, analytics_storage, ad_user_data, ad_personalization — in the correct default-then-update order before any Google tag fires, and reads them back from the network request or Tag Assistant. This card maps each signal, network parameter, and Tag Assistant surface to the misconfiguration it exposes and the fix.

The four signals to verify

By default, no consent mode values are set — unset is not the same as 'denied'. If nothing is configured, GA4 treats ad_storage and analytics_storage as 'granted', so data still flows and masks the misconfiguration.

All seven consent types

What each network parameter carries

Because gcd is always sent, its presence alone is not proof consent mode is configured. Use an explicit default Consent event (and non-l gcd letters) as the real test. Because gcs carries only two of the four signals, a “green” gcs can hide missing ad_user_data / ad_personalization.

gcs value decode (community-documented)

Google does not publish a gcs value table; it confirms only that gcs transmits ad_storage and analytics_storage. The mapping below is community-documented (CookieHub, dumbdata, owntag, Simo Ahava). Verify live against a known consent state.

Format G1xy: x = ad_storage, y = analytics_storage, where 1 is granted and 0 is denied.

Unverified: a dashed / partial gcs (reported as G1--) is claimed by some practitioners to mean “no default set / consent mode not configured,” but no official page confirms it. The leading digit is described in community sources as 1 = signal sent; alternate leading digits are not officially documented.

gcd letter decode (community-documented)

Google does not publish the gcd letter table either; the letters are reverse-engineered by practitioners. The four letters appear in the order ad_storage, analytics_storage, ad_user_data, ad_personalization.

Sources disagree on some letters: an alternate mapping in some references reads q as denied-then-granted, r as granted-then-denied, and adds s for granted-both. Treat exact letter semantics as approximate and verify live against a known consent state.

gcd = 11 [ad_storage] 1 [analytics_storage] 1 [ad_user_data] 1 [ad_personalization] 5
example:  11l1p1u1v5     (starts 11, a 1 separates each signal, terminator digit 5)

GA4 behavior by consent state

Basic vs advanced implementation

Knowing which mode the CMP deployed decides what “correct” looks like before consent.

Required command order

The single most common failure. If the consent code runs out of order, defaults do not work.

For gtag, the gtag('consent','default') / gtag('consent','update') commands must fire before any gtag('config') command. wait_for_update (illustrated as 500 ms; no documented default or maximum) holds tags so an async CMP can send its update first.

Region-scoped defaults

Tag Assistant surfaces

Tag Assistant (tagassistant.google.com, with the Companion Chrome extension) is Google’s sanctioned tool.

For measurement that looks correct on-page but still excludes EEA users, check the server-side surface: GA4 Admin > Consent settings, per data stream (Advertising related consent signals, Behavior analytics consent signals). Notifications there may lag on-page signals by 48-72 hours.

Gotchas

1. gcs stays G100 after “Accept all,” and data remains modeled / low → the banner’s update handler never fires gtag('consent','update',...), so state never leaves its default → select the most recent Consent event in Tag Assistant; if the four signals did not move to granted, wire the accept action to the update command (or, for a CMP, confirm Google consent mode is enabled).
2. Tag Assistant shows “A tag read consent state before a default was set” → the default runs after a tag already read consent — an async CMP, or the default sits below the tag snippet / below gtag('config') → move every default command above all tag snippets, do not load it async, and add wait_for_update (e.g. 500) so an async banner’s update can land first.
3. gcs is missing / empty in the network request → consent mode is not firing before Google’s tags, OR the site runs basic mode (no request before consent), OR the Google tag is blocked from loading → an empty Tag Assistant Consent tab means not-implemented or tag-blocked; confirm the tag loads, a default precedes it, and identify basic (expect no request) vs advanced (expect a gcs=G100 cookieless ping).
4. EEA users are silently denied / low consent rate without ever seeing a banner → region mismatch — the banner and the region-scoped default target different regions → align both to the same regions, audit overlapping region defaults (most specific wins), and test with Chrome location simulation.
5. Remarketing / enhanced conversions / audiences stop for EEA users even though gcs looks fine → ad_user_data and/or ad_personalization were never set; gcs carries only ad_storage + analytics_storage, so a green gcs hides them → check the gcd string (or Tag Assistant API Call) for all four, set defaults and updates for the two v2 signals, and verify GA4 Admin > Consent settings.
6. In server-side GTM you filter for gcs and find nothing → sGTM renames the field to x-ga-gcs in Event Data → read x-ga-gcs, then apply the same decode logic.
7. A site with no consent mode still reports GA4 data normally, so nobody notices → with defaults never set, GA4 treats both storage signals as granted → do not treat “data is flowing” as proof; verify an explicit default Consent event (earliest event) with all four parameters set.
8. Consent mode looks correct but Google Ads shows no impact / modeling results → data thresholds and minimum run time are not met yet — not an implementation bug → keep the implementation running at least 7 full days and meet the data thresholds; do not “fix” a working setup.

Quick recipes

window.dataLayer = window.dataLayer || [];
function gtag() { dataLayer.push(arguments); }
gtag('consent', 'default', {
  ad_storage: 'denied',
  analytics_storage: 'denied',
  ad_user_data: 'denied',
  ad_personalization: 'denied',
  wait_for_update: 500, // ms to let an async CMP send its update first
});

gtag('consent', 'update', {
  ad_storage: 'granted',
  analytics_storage: 'granted',
  ad_user_data: 'granted',
  ad_personalization: 'granted',
});

// Narrow default, scoped to two regions...
gtag('consent', 'default', {
  analytics_storage: 'denied',
  region: ['ES', 'US-AK'],
});
// ...and a broader default for everywhere else.
gtag('consent', 'default', {
  ad_storage: 'denied',
});
// Most specific parameter takes precedence.

// Paste a captured Google request URL (the collect / Ads request).
const url = new URL('PASTE_REQUEST_URL');
const gcs = url.searchParams.get('gcs'); // e.g. "G111"
// Community decode of G1xy (Google does not publish this table):
console.log({
  gcs,
  ad_storage: gcs && gcs[2] === '1' ? 'granted' : 'denied',
  analytics_storage: gcs && gcs[3] === '1' ? 'granted' : 'denied',
});

// In server-side GTM the signal is exposed as x-ga-gcs, not gcs.
const getEventData = require('getEventData');
return getEventData('x-ga-gcs'); // e.g. "G111"

// With ad_storage denied, GCLID / DCLID in consent and key-event pings are redacted.
gtag('set', 'ads_data_redaction', true);

Related

• Hub: Privacy & consent guides
• Lateral: Consent Mode v2 parameter reference · sGTM consent forwarding patterns

Sources

• Consent mode overview — Tag Platform (read 2026-07-20)
• Set up consent mode on websites — Tag Platform (read 2026-07-20)
• Troubleshoot consent mode with Tag Assistant — Tag Platform (read 2026-07-20)
• Consent mode — GA4 Analytics Help (read 2026-07-20)
• Verify and update consent settings in GA4 — Analytics Help (read 2026-07-20)
• Verify consent mode implementation — Tag Manager Help (read 2026-07-20)
• Troubleshoot consent mode — Tag Manager Help (read 2026-07-20)
• Consent Mode troubleshooting for Google Ads — Tag Assistant Help (read 2026-07-20)
• About consent mode — Google Ads Help (read 2026-07-20)
• Updates to consent mode for EEA traffic — Google Ads Help (read 2026-07-20)
• Consent mode reference — Google Ads Help (read 2026-07-20)

Community references (unofficial gcs / gcd decodings, not attributable to Google):

• Consent Mode V2 for Google Tags — Simo Ahava (read 2026-07-20)
• Read and use GCS values in server-side GTM — dumbdata (read 2026-07-20)
• Consent mode v2 signals — CookieHub Docs (read 2026-07-20)
• What the gcs parameter means in GA4 — owntag (read 2026-07-20)