Troubleshooting a P305F code on my 2016 8th gen Malibu

[JTK]

Dual Battery Control Module Performance

I've been chasing this code for a few months. Now a month out from needing a wonderful people's republic of NY mandatory state inspection done, which will not pass with the MIL on, I figured I'd better get serious on it.

The vehicle has been perfect for nearly a year since I bought it. I knew it had the wrong sized battery both under the hood and in the trunk, but both pass load test with my digital tester. No MIL on for nearly a year, etc.

When the P305F first popped up, I added a "stop/start" eliminator jumper harness to the hood switch. They are very inexpensive online. This setup worked like a charm on my 2021 Traverse, but on the 2016 Malibu, it sets a "hood switch circuit performance" code, so it's a no go in the long term. It eliminates the stop/start, but I can't live with a MIL on all the time.

My daughter is the sole driver of this vehicle and she told me the radio had started go out during a stop/start cycle so my immediate thought was the little aux battery in the trunk given this is what this battery is for. The little motorcycle battery that's there is not the right size, but it tests out at ~12.6V and passes load test. I removed this battery for testing purposes.

With the aux battery out, I load tested the under-hood battery which passed for the 600CCA flooded battery it is. When I ran the crank test on it however, it failed miserably at ~9.3V.

The P305F code sets when the ECM detects 3 consecutive starts in the ~9V range.

I ordered an H8 EverStart Platinum from Wally for $179.94. Hopefully that's it. If not, I'll move on to the aux battery, then the dual batter control module/fuse box unit on top of the battery. Isn't stop/start a joy?

My takeaway on this, is don't trust a battery load test by itself. I used a Topdon battery tester FWIW.

 

[twX]

With the aux battery out, I load tested the under-hood battery which passed for the 600CCA flooded battery it is. When I ran the crank test on it however, it failed miserably at ~9.3V.

Was the 9.3 V measured during steady cranking, or was it the minimum voltage detected by your meter? It's normal for the voltage to dip down to 8 or 9 volts for a split second, but it should then recover to 10+ volts.

 

[JTK]

Was the 9.3 V measured during steady cranking, or was it the minimum voltage detected by your meter? It's normal for the voltage to dip down to 8 or 9 volts for a split second, but it should then recover to 10+ volts.

Not sure on that. It's what locked in on my Topdon BT101's "crank test". There was other data displayed on the screen along with the fail message. I'd go back out and test it again and grab a pic, but the vehicle is currently out and about.

Like I say, I do know the code setting criteria for that P305F on this particular GM product is 3 consecutive starts, where battery voltage is pulled into the mid 9VDC range. The OEM battery should be a 900CCA AGM. I've got smaller 600CCA standard battery in there now.

 

[twX]

Not sure on that. It's what locked in on my Topdon BT101's "crank test". There was other data displayed on the screen along with the fail message. I'd go back out and test it again and grab a pic, but the vehicle is currently out and about.

Like I say, I do know the code setting criteria for that P305F on this particular GM product is 3 consecutive starts, where battery voltage is pulled into the mid 9VDC range. The OEM battery should be a 900CCA AGM. I've got smaller 600CCA standard battery in there now.

Okay, I assumed you were just using a multimeter for that test. I'm sure your battery tester knows what's up.

A new battery should fix the code. If the new battery is closer to 900 CCA, it'll probably last quite a lot longer before its performance degrades enough to cause the code to pop up again.

 

[dishdude]

probably the battery

 

[GMBoy]

The most common repair for this condition is battery replacement followed by a bad ground cleaned/repaired.

 

[KrisZ]

That’s why I don’t like the start/stop gimmicks. They are very taxing on the batteries. Whatever minuscule gas saving there are, will be swallowed by the battery replacement costs.

Is there truly no other way to disable this aweful system in a GM? Is the hood switch the only way?
If all else fails, teach your daughter to hit the disable button, at least it’s in a convenient spot. After few days it will be a second habit.

I had a Malibu rental for a week and at day three, I was already hitting that disable button before I put my seatbelt on

 

[JTK]

I had a Malibu rental for a week and at day three, I was already hitting that disable button before I put my seatbelt on

There's no disable button on the 8th Gen Malibus unfortunately. That's what makes it that much more frustrating.

There's hack ways to keep it from coming on like keeping the a/c on max cool, or w/s defrost. Shifting manually, etc.

It's disappointing the hood switch bypass harness isn't going to work out on it either.

I'm still waiting on the new main battery.

 

[JTK]

I just got done installing that monster H8 900CCA AGM battery in the Malibu. That is by far the largest, heaviest battery I've ever replaced in a 4cyl, run of the mill car. I actually felt the front end squat a tiny bit when landing that sucker in the tray.

I cleared the code, took it for a test drive, let it stop/start 3x and so far so good. No codes. We'll see how it goes.

In the event anyone needs to, a 96R 590cca battery will work in a 2013-2016 8th gen malibu. It's not nearly as long and the hold down tab doesn't reach, but it fits the tray and has all the proper recesses in the right spots for the plastic fuse boxes and whatnot to snap into place. Like I say, this junk yard battery was put in my malibu before I bought it.