DTC P1549

DTC P1549:  Charging System High Voltage

General Description 

Courtesy of HONDA, U.S.A., INC.

The alternator is driven by the engine, and it generates electricity to supply the necessary power to the electrical system and to charge the 12 volt 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 powertrain control module (PCM)). The alternator output signal is sent to the PCM, and it varies according to the 12 volt 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 PCM detects a malfunction and stores a DTC.

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

Execution	Continuous
Sequence	None
Duration	60 seconds or more
DTC Type	One drive cycle, MIL off
OBD Status	PASSED/FAILED/NOT COMPLETED (STILL TESTING)

Enable Conditions 

Condition	Minimum	Maximum
Engine speed[ENGINE SPEED]	500 rpm	-

[ ]: HDS Parameter

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, regulator failure)
• PCM 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 PCM 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 12 volt battery.