P23A9Communication Fault - Forced Engine Shutdown
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- P23A9 records that the engine was stopped, or kept from running, because the engine module lost contact with a control unit whose messages it needs to operate the engine safely. The title names only the consequence; which data link is meant is defined by each manufacturer, and none publishes P23A9. The underlying network fault normally shows up as a separate U code in the same or another module. CARB requires digital inputs to be monitored for missing communication. A comparable published check is GM's P06AF in its 2019 tables, where the ECM verifies a message pattern from the transmission module and may stop the engine on a mismatch. For the driver: the engine dies or refuses to restart; check CAN wiring and termination as well as supply and grounds of the modules involved.
- What you may notice
- Engine stops while driving or does not start
- Several U codes and warning messages from other modules
- MIL or other warning lights on
- Likely causes
- LikelyDamaged CAN wiring, connector or termination
- PossiblePartner module without power or ground, or low battery voltage
- PossibleFailed or wrongly programmed partner module
- RareSoftware versions of the modules not matching after repair
- Repair
- Hard · Usually a job for a workshop.Typical cost: €0 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.