Suddenly reading 13V

[Bluetick]

My voltage has always read 14V. Suddenly it's reading 13V. What could be causing that?

 

[Ken226]

My voltage has always read 14V. Suddenly it's reading 13V. What could be causing that?

How are you measuring this? With a multimeter, or something else?
Engine idling?


Without enough context or info, I'm left to guess.

The alternators output while idling is controlled by the PCM. It reads the overall system voltage, and sends a pulse width modulated signal to the alternator to control the alternators charging output.

If your battery is weak, in a low voltage state, or some accessory system is drawing alot of power, the PCM increases the pulsewidth to the alternators field input, which increases the alternators output voltage.

If your battery is strong and fully charged, and/or there isn't much load from accessory systems, the PCM reduce the pulsewidth to the alternator and reduces it's charging output.



So, if your charging output while the engine is idling is only 13 volts, it could be alot of things. Possibly you have a new battery that is in great health, fully charged, and the PCM is happy with the state of things and doesn't feel the need to max out the charging output or risk overcharging and damaging the battery.

OR, You're alternator is bad, and the PCM is trying desperately to max out the signal to the alternator but the alternator just isn't responding. Or, something else.


Do you have any symptoms? Any codes set? Some other reason to think that there is a problem?

If you have a bidirectional scan tool or AlfaOBD you can look at live data that will show your system voltage, sensed voltage and the voltage the PCM is aiming for.