GM OBD Trouble Code 16

System Voltage Too Low

The Engine Control Module monitors system voltage internally. If system voltage becomes too high or too low, electrical devices on the vehicle may not function properly. They could also be damaged.

Fault Code Description

  • 16 - System Voltage too low (low output from alternator)


  • Charging system warning indicator can come on
  • Voltage gauge reading is low
  • The engine runs poorly or stalls due to low system voltage. When the system voltage gets below ~9v, the ECM and ignition system can no longer function correctly, which causes the engine to stall.

Common Problems

  • A failed alternator would be the most common cause for a code 16
  • A complete charging system test should be performed before replacing the alternator. If the charging system checks out okay, the fault could be with the ECM power or ground circuits, or an internal fault.

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