A part number is not a barcode. Channels know the difference.
When we scanned 65 aftermarket catalogs, the most common finding by a wide margin was a product page carrying a manufacturer part number and no barcode. Seventy-three of 128 pages.
We grade that as a warning rather than a blocker, and people ask why. The honest answer is that it depends, and the thing it depends on is not the one most people expect.
“No barcode” describes two different situations
There is a product that has a barcode which nobody put in the feed.
There is a product that genuinely has no barcode, because it is machined to order, or private-label, or a bracket your shop welds in batches of forty.
To you these feel similar. Both show up as an empty field. To a channel they are opposite situations, and the difference is not something it can work out on its own. An empty field is an empty field. Nothing in it says which of the two you meant.
That ambiguity is the actual problem. Not the missing barcode.
What Google’s rule actually says
Google’s rule is narrower than the folklore around it. GTIN is strongly recommended for products the manufacturer assigned one to. If yours has one and you leave it out, listings “may have limited visibility”, in Google’s phrasing, and it warns that accurate matching cannot be assured. That is degraded performance, not a rejection. Your product does not disappear. It just competes worse, quietly, forever.
Brand is the stricter requirement. It is required for new products in every category except movies, books, and musical recordings. MPN becomes required specifically when the product has no manufacturer-assigned GTIN.
And there is an attribute for the second situation above. If your product genuinely has no
GTIN, you set identifier_exists to no and submit brand and MPN instead. That is you
telling Google the field is empty on purpose.
So the failure mode is not “we have no barcodes.” It is “we have no barcodes and never said so.” One is a supported configuration. The other is an unanswered question, and the channel resolves it against you.
A wrong barcode is worse than no barcode
This is the part that reverses most people’s intuition.
Missing GTIN gets you limited visibility. An incorrect GTIN gets the product disapproved outright. The check digit is validated, restricted prefix ranges are rejected, and every variant needs its own.
So the instinct to fill the field in to make the warning go away, by reusing a similar product’s code, or by generating something plausible, converts a soft penalty into a hard one. We have seen catalogs where a well-meaning cleanup did exactly this.
If you do not have the number, do not invent one. Declare that you do not have it.
Amazon handles the same question completely differently
Google lets you self-declare. Amazon makes you apply.
Amazon’s equivalent is a product ID exemption, and automotive parts are explicitly an eligible category. But it is an application, not a checkbox. You submit photographs of the product and its packaging from multiple angles, and you wait for a decision.
There is also a trap worth knowing before you start. If your brand already assigns GS1 barcodes to its other products, Amazon will not grant an exemption for the ones that lack them. A brand with a GS1 prefix is expected to use it. So the mid-size manufacturer who barcoded the fast movers years ago and never went back for the long tail is exactly the company that cannot exempt its way out.
Same underlying fact about your catalog. Two channels, two entirely different pieces of work.
What to do about it
Split the catalog in two, because the answer differs by group.
For products that have a manufacturer-assigned GTIN, find it and populate it. This is usually a data-entry problem rather than a systems problem, and it is the group where doing nothing costs you real visibility.
For products that genuinely have none, declare it. Set identifier_exists to no on
Google, make sure brand and MPN are populated and accurate, and start the Amazon exemption
early, because it involves photography and a queue.
For everything, never guess a number.
Most catalogs we look at have not made the split, which is why the field is simply blank across the board and the same warning appears on every product. The fix is rarely difficult. It is just nobody’s job, so it does not happen, and nothing ever tells you it is costing anything.
Sources: Google Merchant Center on the GTIN attribute and unique product identifiers. Channel requirements change; these were checked on 11 August 2026.