Trouble Code 8E04

Yesterday I discovered that the battery in my Boxster was completely discharged. The battery is only a few months old, and the car was driven about 5 days before. I recharged the battery overnight. After investigating and clearing a bunch of trouble codes, one persists - 8E04, PCM Coding. I can't find a thing on it. Does anyone have an idea what this means? This is the second time I've been surprised by a dead battery. The first time I attributed it to excessive age. This time will require some investigation. And I'd like to find the doofus that thought it was a good idea to require electrical power to access the battery. Geez.

It sounds like you're using a Porsche -capable reader, but please confirm just in case. Sounds like the code is clear - PCM has lost some of its coding information. I have seen one other user say this happened when their battery died in the car. You may just have to get in and re-code some modules or settings to get this to resolve? Alternatively, it could disappear after driving a bit... something may "wake up" afterwards and work properly. I agree, deeper troubleshooting is warranted for the power issue. Also note that once a battery is dead, it really needs to be replaced... they can come back "kinda" after recharging, but they are never the same. Swap it out (should be low-cost especially since it's only a few months old - most batteries are warrantied for at least a year, and then prorated after that).

What tool are you using to read the codes? "8E04" is not a Porsche code number, so that's why you've found nothing on it. Also - question - stock radio/ PCM or a replacement "headunit"? The replacements normally can cause lots of stored CanBus error codes since they don't respond to modules expecting to find a PCM in the system. There are several threads that go into detail tracking down parasitic current draw issues.. might be worth a bit of searching.

The reader I'm using is an Autel MX-808 if I remember correctly. Will check that in a bit. The radio is stock. Deeper investigation will probably have to wait until next week.

The dead battery is still a bit of a mystery. I disconnected it, charged it, and it tested good. I measured the current draw when reconnected - 1900mA for about a minute, then 50mA continuous after that. Seems reasonable. I even put my GoPro camera in the trunk and frunk to verify that the lights were going out when closed. Intermittent electrical problems are such a joy.

Odd. Got an error message when making the previous post, then a double-post of the same message. Perhaps a kind moderator will delete this post. Thanks!

No problem about the double posts... don't worry about it. So, did the battery actually die out? If so, it's likely damaged... plan to replace it. Lead acid batteries do not like to be discharged below a certain level, and they can "test good" but still be bad. These cars are VERY sensitive to bad batteries, so that would be the first thing to replace. HOWEVER, I fully support using it until you find the source of the drain. No sense in damaging a new battery if you still have a drain issue. That said, how old is the existing battery - it could be bad and unable to hold capacity, hence why it went dead in the first place.

The battery is 5 months old - Autozone Duralast Platinum H7-AGM. And yes, the battery was completely dead a few days ago. I had to put power on the system through the fuse box connector for several seconds before I could unlatch the frunk. I used a motorcycle battery for a power source. It has me thinking about devising some way to manually open it. Too hot to drive around here for the next few days, so I'll watch to see what it does.

Ok, well if it's that new, then you may want to watch the warranty process and replace it under warranty before it hits the prorated term. The good news is that it seems to be 3 years for the Platinum, so you have plenty of time, but I would say you should certainly replace it, since it was dead. Timing is the only question (ie you may want to chase the drain first before having to swap it potenitally AGAIN afterwards). You don't need to drive the car around to do the drain testing... get a meter, and start pulling the fuses and see what happens to the readings. It's a simple process - hardest part is getting the meter and setting it up for current-readings.

I thought the 50mA reading I got for a quiescent current was nothing to be concerned about. The only peculiarity I noticed when this began was that the alarm horn was disconnected. Not sure why, or why it would matter. Sitting in the car for the last 24 hours, the battery voltage has not dropped significantly - 12.50V down to 12.47V, and I've opened the doors a couple of times. At this point, all I can guess is that something stayed powered on last week, but is not presently consuming power. I'll continue to watch, and I very much like your idea of experimenting with the old battery in place.

Agreed, 50mA seems fine. Like you said, maybe you just got unlucky and something was left on by mistake. That's not usually a problem, since the car will shut off things after 15 minutes (frunk light, for example)... but who knows. Have you had anything plugged into the cigarette lighter plugs? Or maybe an OBD reader? These are both unswitched power, so they may remain on and open all the time... ?

Well, this one goes into the mysterious Could not duplicate collection. Sitting idle for a week showed no significant decline in battery voltage. All error codes have cleared. Still, it remains in the back of my mind. I'm going to shop for a portable jump starter. Fortune favors the prepared.