P305F Code: Dual Battery Control Module Performance (Chevy Malibu & Impala Guide)

P305F on a Chevrolet is "Dual Battery Control Module Performance." It is a narrow code: it applies to the 2014–2016 Malibu and Malibu Limited and the 2014–2016 Impala with the 2.5L and Stop/Start (RPO KL9), which use two batteries and a module that manages them. Two GM instructions save money on this one. First, GM's preliminary information said in so many words: do not replace the ECM for this code. Second, the battery test GM requires is a state-of-health test on the auxiliary battery — a battery that reads fully charged can still be the problem.

What Does P305F Mean?

P305F is set by the engine computer when the dual battery control function is not performing as expected. On these cars, a Dual Battery Isolation Module (DBIM) built into the battery distribution fuse block manages the relationship between the main battery and an auxiliary battery, so that the electrical system stays stable while the engine shuts off and restarts at stops.

GM's exact setting criteria are in service information we could not open, so we will not quote a voltage threshold. Some websites state one; none we found cited a GM source for it. What GM's bulletins do make clear is where the fault is usually found: the auxiliary battery, a ground connection, the harness near the battery tray, or the fuse block assembly that contains the module.

Which Chevrolets Set P305F

GM's documents name:

• 2014–2015 Chevrolet Malibu with the 2.5L (LKW) and Stop/Start
• 2016 Chevrolet Malibu Limited with the 2.5L (LCV) and Stop/Start
• 2014–2016 Chevrolet Impala with the 2.5L (VIN 1) and Stop/Start

A separate GM engineering information document covers P305F on the 2014–2018 Impala and Malibu with smoke or a burning odor (see below), which is a broader year range.

We found no GM document tying P305F to the Silverado, Equinox, Cruze, Bolt or any Duramax. If a site lists those, ask what it is based on.

How the Dual-Battery System Works

A Stop/Start car shuts the engine off at a stop and restarts it when you lift off the brake. Every restart is a large current draw. If the radio, screen and modules shared one battery with the starter, voltage would dip on every restart.

The 2.5L Stop/Start Malibu and Impala solve this with two batteries. The main battery cranks the engine. The auxiliary battery supports the electrical system during restarts. The DBIM, inside the battery distribution fuse block, isolates and connects them as needed.

That makes the auxiliary battery a working part, not a backup — and a weak one shows up as a performance fault in the module that relies on it.

P305F Is Not a DC/DC Converter Code

The codes around it are easy to confuse. GM uses P305D and P305E for "DC/DC Converter Crank Control Circuit High/Low Voltage" — a different system, found on vehicles such as the 2016–2018 Malibu with wireless charging and the 2021+ Tahoe, Suburban and 2022+ Silverado 1500.

P305F sits next to those numerically but belongs to the dual-battery design. The diagnosis, parts and vehicles are different. Don't apply DC/DC converter advice to a P305F.

GM's Four-Step Procedure

GM bulletin 18-NA-367 ("Diagnostic Tip for MIL Illuminated with DTC P305F, P058B and/or P058D," December 2018, revised May 2019 to add the Impala) lists the causes GM found: a loose ring terminal at the negative battery terminal, fretting or corrosion on the female pins of the 4-pin connector, a loose splice in the harness ground circuit, and a defective battery control module.

The P305F procedure:

1. Test the auxiliary battery's state of health with GM's GR8 tester — not just its state of charge. Replace it if it tests low.
2. Measure resistance from the DBIM to ground G103 while wiggling the harness and the negative terminal. More than 0.5 ohm, or a change of more than 1 ohm while wiggling, means inspect the ground connections and the harness splice about 1.5 feet from the connector end.
3. Check that the engine harness is not pinched under the main battery tray.
4. Replace the battery distribution fuse block and harness connector if the above check out. GM parts: fuse block 23223079, connector kit 13581092.

The earlier preliminary information, PI1412 (February 2015, 2014–2015 Malibu), carried the line that should stop an expensive mistake: "Do NOT replace the ECM for this DTC." It directed the same checks — ground G103, the harness under the tray, both battery cables, and the auxiliary battery.

For P058B and P058D (battery sensor codes) on the same cars, GM adds a check of the ground ring orientation at the battery sensor module and a torque of 5 N·m (44 lb-in).

Smoke or Burning Smell

A separate GM engineering information document (April 2018) covers 2014–2018 Impala and Malibu with smoke or a burning odor from under the hood, check engine light on, and P305F or P058D. GM's steps include inspecting the DBIM for heat deformation, checking DBIM ground resistance and checking both batteries' state of charge, then contacting GM engineering.

If you smell burning, stop and have it inspected. A high-resistance connection in a battery circuit generates heat, and that is not something to drive around with.

Symptoms of P305F

• Check engine light on
• Auto Stop/Start not operating
• Smoke or burning smell under the hood on some 2014–2018 Impala and Malibu (GM engineering information)
• Possible electrical glitches during restarts
• P058B or P058D stored alongside

Causes and How to Confirm Each

How Is P305F Diagnosed?

1. Confirm the vehicle. A 2014–2016 Malibu, Malibu Limited or Impala 2.5L with Stop/Start is the P305F application.
2. If there is any smoke or burning smell, stop and inspect the DBIM for heat damage before going further.
3. Test the auxiliary battery's state of health. Replace it if it is weak.
4. Check the negative terminal ring and both battery cables.
5. Measure DBIM-to-G103 ground resistance while wiggling the harness.
6. Remove the battery tray and check for a pinched harness.
7. Inspect the 4-pin connector pins.
8. Replace the battery distribution fuse block and connector only after the steps above pass.
9. Clear the code and drive through several stop/start events to confirm.

Parts and Cost

GM Documents That Name P305F

Have a dealer check your VIN against current bulletins rather than relying on any article, including this one.

What Other P305F Pages Get Wrong

• Replacing the ECM. GM's own instruction says not to.
• Testing battery voltage only. GM requires a state-of-health test. A fully charged weak battery will pass a voltage check.
• Calling P305F a DC/DC converter code. That is P305D and P305E, a different system on different vehicles.
• Quoting a voltage threshold as GM fact. We found no GM source for the numbers circulating online.
• Listing it for Silverados and Equinoxes. GM's documents name the Stop/Start Malibu and Impala.
• Ignoring a burning smell. GM has a document specifically on heat deformation of the module.

Frequently Asked Questions

Is P305F serious?

Usually it disables Stop/Start and turns on the light. But GM has documented smoke or a burning odor with P305F on some Impala and Malibu models, so if you smell anything burning, stop and have it inspected before driving further.

Do I need a new auxiliary battery?

Possibly — it is GM's first suspect. Test its state of health with a conductance-type battery tester, not just its voltage. Replace it if it tests weak.

Should the ECM be replaced for P305F?

No. GM's PI1412 states "Do NOT replace the ECM for this DTC." The battery, grounds, harness and fuse block come first.

What is the Dual Battery Isolation Module?

The module that manages the main and auxiliary batteries on Stop/Start Malibu and Impala models. It is built into the battery distribution fuse block, so GM services it by replacing that block (part 23223079).

Can I drive without Stop/Start working?

Yes. The engine simply stays running at stops. The car is otherwise normal unless there is a burning smell or another electrical symptom.

Is P305F the same as P305D?

No. P305D and P305E are DC/DC converter crank control codes on other vehicles. P305F is dual battery control module performance on the 2.5L Stop/Start Malibu and Impala.