Google rolled out Channel Diagnostics for Performance Max starting July 1. It sits inside Insights & Reports > Channel Performance — the same section that shows budget distribution across Search, Shopping, YouTube, Display, Discover, Gmail, and Maps.
The new diagnostics layer does something the existing report couldn't: it shows which channels your campaign was excluded from and exactly which asset types caused the exclusion. Missing video? YouTube and Discover flag it. Disapproved headline? Search and Shopping surface it. Wrong image dimensions? Display goes dark.
The feature is in limited testing and not yet in every account. But the problem it surfaces exists in every account running PMax without a complete asset set.
What was actually happening
PMax has been criticized since launch for hiding its own logic. The channel performance report added last year helped — you could finally see where budget went. It couldn't tell you why certain channels got almost nothing.
Here's what's been happening in a lot of accounts: an asset group with headlines, descriptions, and a Merchant Center feed runs fine on Search and Shopping. It gets zero YouTube delivery because there's no video. Zero Display delivery because the image assets don't cover the required dimensions. The campaign runs, reports a ROAS, and looks fine from the outside. Nothing in the UI tells you that four of your six channels were never activated.
That's not a bid problem. It's a setup problem that has been invisible until now.
The manual audit (for everyone without the feature yet)
Channel Diagnostics may not be in your account. The fix is the same either way. Go into each asset group and check:
- Video assets. YouTube and Discover require them. A 15–30 second video is the minimum for those channels to activate at all.
- Image assets. Display requires images in multiple formats. A single landscape and one square aren't enough — check the recommended dimensions in the asset group editor.
- Merchant Center connection. If Shopping shows near-zero in your channel breakdown, verify the feed link at the campaign level. Policy violations in the feed don't always surface as campaign-level alerts.
- Disapproval status. Go to Assets > View details, filter for disapproved. A disapproved asset quietly removes an entire asset type from a channel's eligibility. It can sit there for weeks without triggering any notification.
Most PMax accounts running without a regular asset review have at least one of these gaps. The diagnostics will confirm which one.
Why this changes the math
Google's internal benchmark for AI Max is a 7% lift in conversions with the full feature suite enabled. That figure assumes complete, approved asset groups serving across all eligible channels. A PMax running on two channels out of six doesn't get a smaller version of that number — it gets a fundamentally different campaign: fewer impressions, narrower signal collection, slower optimization.
The whole premise of PMax is cross-channel demand capture: consideration on YouTube, retargeting on Display, purchase intent on Search and Shopping. If your campaign is only active on two of those surfaces, you're paying for a machine that's been running at partial capacity. The ROAS may look acceptable, but you're comparing against a floor that's been artificially lowered by missing channels.
What to fix and in what order
Start with video. Adding a video asset to a PMax campaign that has never had one typically shifts channel delivery within 48 to 72 hours. It's the highest-leverage fix for accounts that show weak YouTube and Discover spend.
Then address image assets. Gaps in dimensions are easy to miss because the campaign still serves — just not on the channels that need the missing formats.
After that, run a disapproval check across all asset groups. One disapproved asset can block a channel for weeks without any campaign-level alert.
If your account already has complete asset groups and still shows weak delivery on specific channels, Channel Diagnostics will tell you something else is limiting performance — brand safety exclusions, bid constraints, or audience signal mismatch. Those are separate problems, but now there's a tool that distinguishes between a creative gap and a structural one.
PMax got channel-level transparency this week. What you find in the diagnostics tells you whether the campaign has been running at full capacity, or something closer to half.
If you want to see how your PMax structure compares against accounts in your category, the free audit at Gromerce pulls the key setup signals in about three minutes.
Sources: Search Engine Land, Search Engine Roundtable, Google Ads Help, July 2026
