Advanced Diagnostics

Advanced Diagnostics - DTC P1549: Charging System High Voltage (Engine Type: K24Z7)

General Description






The alternator is driven by the engine, and it generates electricity to supply the necessary power to the electrical system and to charge the battery. The alternator voltage target values from 12.5 V to 14.5 V are achieved by switching the alternator control mode (controlled by the engine control module (ECM)). The alternator output signal is sent to the ECM, and it varies according to the battery's state of charge, the electrical load, and the engine speed. When the FI_MAIN_RLY_OUT terminal voltage is a set value for a set time, the ECM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status






Enable Conditions






Malfunction Threshold
The FI_MAIN_RLY_OUT terminal voltage is 16.0 V or more for at least 60 seconds.

Possible Cause

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.

- Alternator failure (field coil E side short to ground, voltage regulator failure)
- ECM internal circuit failure

Diagnosis Details

Conditions for setting the DTC
When a malfunction is detected, a Pending DTC, a Confirmed DTC, and the freeze data are stored in the ECM memory. The MIL does not come on.

Conditions for clearing the DTC
The Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.