Late-model Chevy Malibu’s and Impala’s use two batteries to help power their auto-start feature. The P305F code indicates a performance issue with the module that controls the two batteries. In reality, P305F is usually caused by low voltage in the auxiliary battery.
P305F Definition: Dual Battery Control Module Performance
Here’s what’s happening if your Impala or Malibu has P305F.
Dual Battery Control Module
When you usually start a vehicle, the lights dim, the radio turns off, and the climate control may not work. If you are in stop-and-go traffic, that could get annoying as your vehicle starts and stops. The dual battery setup is GM’s answer to this problem in the Malibu and Impala.
A small auxiliary battery (usually in the trunk, check your owner’s manual if you don’t see it back there) keeps the voltage level consistent when the auto start feature is engaged.
The Dual Battery Control Module regulates the voltage when the Powertrain Control Module (PCM) cuts power to the engine.
Performance
The secondary battery voltage must be below 8.9 volts for 2 out of 3 engine starts. If it falls below that threshold, P305F will be stored in the PCM’s memory, and the check engine light will come on. Auto start/stop will be disabled.
P305F Symptoms: Malibu/Impala
Here are the most common symptoms of P305F in the Chevy Malibu and Impala. It should not be considered a breakdown risk. The secondary battery will not be relied upon until the problem is fixed.
- Check engine light
- A slight decrease in fuel mileage
- Auto start/stop will be disabled
P305F Causes
Here are the most common causes of P305F in the Chevy Impala and Malibu:
Bad Secondary Battery
A bad secondary battery is the most common cause of P305F. The good news is that they are easy to get to and test. The video below outlines how to test it.
Once you replace the battery, go ahead and clear the code. You’ll need to turn the vehicle on and off four or five times to verify the code doesn’t come back.
Other Causes
While replacing the secondary battery will fix P305F most of the time, here are the other (less common) causes.
- Battery Ground– Check the ground connections at both batteries. A bad ground at either one can cause P305F.
- Aux Battery Connection– Make sure the positive battery cable is bolted on tightly and corrosion-free.
- Dual Battery Control Module– Check the connections at the module. Verify they are all tight.
- Battery Fuse Box/Block
Conclusion
P305F is most commonly fixed by testing and replacing the aux battery. If the battery is vented, make sure to replace it with another vented battery.