When your barcodes do not scan: a checklist

十一月 14, 2019
By John Nachtrieb, Barcode-test LLC. Barcode quality trainer, consultant and testing service provider


When a barcode doesn’t scan it is almost always an emergency—a growing and unhappy checkout line, a patient lying in a hospital bed waiting for medication, or a chargeback notification from your trading partner.

Immediately after the stress of the moment and that sinking feeling in your gut, the real problem is what to do? If the scanner cannot read the barcode, what is the procedure for sorting out the mystery of what is wrong?



Here is a checklist—and it involves a low power magnifier. I find 8 and 10 power to be ideal.

  • Print Gain Examine the bars and spaces in the barcode. The narrow bars and spaces should be equal in width. If the narrow spaces are much thinner than the narrow bars, the barcode is overprinted. If the narrow spaces are almost obliterated, the scanner might not be detecting them—and this will cause a scan failure.
  • Notice any voids in the bars or spots in the spaces. A scanner could detect a void in a bar as a space and a spot in a space as a bar. That can cause a scanner to mis-count the bars and spaces which makes it impossible for it to determine what kind of symbol it is—and therefore fail to decode.
  • Take a close look at the quiet zones. This is the area to the left and right of a 1D barcode and generally, it should be at least ¼”. Actually, it varies depending on the symbol size and type, but if it is too small, the scan can fail. For 2D symbols the quiet zone should be about 1/8 to ¼ inch on all four sides—but again this varies.




  • A barcode with an addendum, such as a GS1 EAN-13 (Bookland EAN) can fail to scan if the price code is improperly located too close to the primary barcode.
  • Notice the background against which the barcode is printed. Is it uniformly bright and high-contrast? Any sort of pattern or screen will confuse the scanner and cause a scan failure. Are there objects behind the barcode, such as products in a package or bag that could cause the background contrast to vary.
  • Inspect the dark bars or elements of the barcode. Are they uniformly low contrast? If it varies for any reason, including smudges, creases or loose-fitting shrink-wrap or laminate, it can add reflective signals that confuse the scanner.
  • If a thermal printer produced the barcode, look closely to see if there are tiny parallel or perpendicular lines in the barcode. When printed in picket fence orientation, these thin lines could also appear in text or graphics above or below the barcode. Burned out pixels in the thermal print head cause extraneous lines that appear to the scanner as spaces.
  • Many—but not all–barcodes have check digits. A scanner configured to expect a check digit could fail to scan a barcode without a check digit.
  • Scanners can go out of calibration without warning or symptoms of malfunctioning. It is wise to retain a test barcode of known quality to use as a scanner confirmation tool.




Bear in mind that a verifier is also a scanner—a scanner with sophisticated software that applies a highly sophisticated analysis to the captured data. This checklist applies equally to a scan failure with a barcode verifier.

Visit the Barcode-Test website for additional information.

An Error Occurred.