DTC Advanced Diagnostics: P1549
DTC P1549:Charging System High Voltage

General Description

Driven by the engine, the alternator 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
Execution
Continuous
Sequence
None
Duration
60 seconds or more
DTC Type
One drive cycle, MIL off

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.