CO-166Contractual ObligationEligibility
CO-166 Denial Code: Submitted after payer's responsibility ended
The claim arrived after this payer stopped being responsible for the plan — the plan changed administrators or terminated.
Why CO-166 happens
- ●Employer switched TPAs/carriers; runout period expired
- ●Claim sent to the old administrator after cutover
How to fix a CO-166 denial
- 1
Identify the successor administrator from the member/employer and rebill there
- 2
Cite original timely submission if the successor balks on filing limits
How to prevent it
Re-verify payer identity at each visit — administrator changes hide behind unchanged member IDs.
Drowning in CO-166 denials?
OakClaim works every denial within 48 hours and builds prevention rules so they stop recurring.