OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P23A9

Communication Fault Forced Engine Shutdown

A safety-critical communication loss between control modules has triggered a forced engine shutdown. The ECU could not validate signals it needs to operate safely (e.g. throttle commands, brake state) and stopped the engine.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / number3 / A9

Possible causes

  • Bus communication lost high
  • Gateway module routing CAN messages incorrectly low
  • CAN terminating resistor (120 Ω) drifted out of spec low

Inspection / repair

  • Difficulty: hard
  • DIY: shop recommended
  • Estimated cost: 200–2000 €
  • Estimated time: 1–6 h
  • Component: powertrain bus
  • Component: ecm
  • MIL / check engine light

Sources

References

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication