U0198 on Mazda vehicles

A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.

Bulletins and campaigns Mazda filed with NHTSA whose summary names U0198. Quote the document number at the service desk — it is a diagnosis the maker has already written down.

• SA-060-25 Service bulletin
  2025-12-17 · Unknown Or Other
• Some customers may experience a message "TCU Malfunction. Have the Vehicle Inspected" in the instrument cluster. The following DTC's may be stored: B1252:87-8B:TCU - COMMUNICATION ERROR WITH CONNECTIVITY MASTER UNIT (CMU) • U0198:00-03:CMU - COMMUNICATION ERROR WITH EMERGENCY CALL UNIT/TELEMATICS COMMUNICATION UNIT
• SA-012-26 Service bulletin
  2026-02-27 · Unknown Or Other
• This Service Alert supersedes the previously issued SA(s) listed below. The changes are noted in Red. SA-060/25 12/16/25 Some customers may experience a message "TCU Malfunction. Have the Vehicle Inspected" in the instrument cluster. Additional symptoms that may occur: Connected Vehicle One Time Passcode (OTP) may fail. Connected Vehicle Remote functions may fail. The following DTC's may be stored
• SA-012-26a Service bulletin
  2026-03-04 · Electrical System
• This Service Alert supersedes the previously issued SA(s) listed below. The changes are noted in Red. SA-012/26 02/26/2026 DESCRIPTION Some customers may experience a message "TCU Malfunction. Have the Vehicle Inspected" in the instrument cluster. Additional symptoms that may occur: Connected Vehicle One Time Passcode (OTP) may fail. Connected Vehicle Remote functions may fail. The following DTC'
• SA-012-26b Service bulletin
  2026-04-18 · Electrical System
• Some customers may experience a message "TCU Malfunction. Have the Vehicle Inspected" in the instrument cluster. Additional symptoms that may occur: Connected Vehicle One Time Passcode (OTP) may fail. • Connected Vehicle Remote functions may fail. • The following DTC's may be stored: B1252:87-8B:TCU - COMMUNICATION ERROR WITH CONNECTIVITY MASTER UNIT (CMU) • U0198:00-03:CMU - COMMUNICATION ERROR W

A stored code names the test that failed, never the part that caused it. The record above is what Mazda and its owners have filed about it; the code’s page across every make has the whole file.