Metro 2 ECOA Code 3: Authorized User

Specification

Code	3
Meaning	Authorized User
Field	ECOA Code (Field 10)
Record	Base Segment
Length / position	1 char · 63–63
Category	Access Without Liability
CRRG reference	CRRG ECOA Code table (Base Segment)

An authorized user cannot be sued for the balance. They did not apply, did not sign, and have no obligation to repay. Everything about how the tradeline is treated on their file follows from that one fact.
The designator belongs on the associated consumer's segment, not on the Base Segment. The account still has a liable primary consumer, and that consumer keeps their own code (usually 1).
Does not mean "secondary borrower". A person who signed as a backstop is a co-maker or guarantor (code 5), and a person who signed as an equal obligor is joint (code 2). Both of those are liable; an authorized user is not.
Does not mean "the account does not appear on their report". It generally does appear, which is precisely why the code matters: the designator is the only thing telling every downstream reader that this person is not responsible for the balance.
Identification requirements are stricter in practice for authorized users than for the primary borrower, because the furnisher often has less information about someone who never completed an application.

1A parent adds an 18-year-old to an existing revolving card so the student can build a file, and the student receives a card but never signs the cardholder agreement.
2A card issuer adds a spouse as an authorized user on an account the other spouse applied for and signed alone.
3A small-business owner issues an employee card on a personal-liability account where only the owner is obligated.
4A caregiver is given card access to handle a relative's household purchases without being added to the contract.

Report the authorized user in a J1 or J2 segment with ECOA 3 and leave the Base Segment designator alone.
Never apply joint-obligor logic to an authorized user. Do not treat the delinquency as theirs to cure, and do not add them to collection or charge-off correspondence as an obligor.
Capture identifying data carefully. Authorized users are the segment most likely to be missing a Social Security Number or date of birth, and a mismatched authorized user attaches someone else's tradeline to the wrong file.
Remove an authorized user with ECOA Z when their access ends. Do not simply stop sending the segment, and do not delete the whole tradeline to get rid of one non-liable user.
Do not use ECOA 3 to soften the reporting for a co-borrower you would rather not report against. The designator describes the contract, not your preference.

A file can be structurally valid and still be wrong. These are the cross-field conditions ECOA Code 3 has to satisfy.

ECOA 3 belongs in the associated-consumer segment. A Base Segment reporting ECOA 3 as the primary consumer's designator has no liable party on the tradeline at all, which is a contradiction the associated-consumer edits are designed to catch.
An authorized-user segment does not change any account-level field. Current Balance, Amount Past Due, Account Status, Payment Rating and Date of First Delinquency continue to describe the obligation of the liable consumer.
Where identification is thin, the associated segment's required fields still have to be populated. A J1 segment missing surname or first name fails validation regardless of the ECOA code it carries.
Because an authorized user is not liable, ECOA 3 must not appear on a segment you are also treating as a co-signer. Pick 2 or 5 if the person actually signed.
Ending the relationship uses ECOA Z on that consumer, not Account Status DA, which would delete the tradeline from the liable consumer's file too.