RaidersR1

This came up while driving. Battery or alternator?

semicycler

While driving? Then likely the battery is not charging. What year? Early 997.1's have a known issue with the cable harness between the alternator, starter, and battery.

Battery failures are common. Alternators themselves not so much. The cable between them for earlier models is a common failure too, although that tends to be weak cold starts instead.

First make sure the serpentine belt is still there. Seems silly but no belt, no charging. Next check the age on the battery itself. Some have a sticker on them with mm/yy or ww/yy (work week or calendar week). Others have a date code stamped near or on one of the terminals. If it's the original battery or if it's older than about 4 years or so I'd replace regardless of the true source of the problem because you will have battery issues soon anyway.

Use a multimeter and measure the voltage at the battery terminals when off. A quick google search should tell you if the voltage is acceptable. Generally closer to 12V for good batteries, closer to 11V or less for bad batteries. I like to see 11.8 or higher. You might need to charge the battery with a trickle charger first to get a valid reading.

Next measure voltage while idling at both the battery and the alternator. Careful not to get your hands or clothes caught in the engine while idling. The voltage should be well over 12V, close to 14V or so, and the drop between the alternator and battery less than 0.5V. A large drop is the harness. A voltage too low is the alternator.

NeilW

Good advice above. Mine recently threw the same error and after performing the necessary checks, turned out to be the alternator itself. A new one was £400-500, so I took a chance and purchased one, new from eBay for £139. When comparing with the old one, the casings looked identical with some minor differences in the plastic mouldings. It appeared to be well made though. Took me about an hour and a half to change it. Think I only used one spanner and one socket. Good luck.

RaidersR1

I already have the hot start issue and now it appears I'm not charging my battery. I just recently charged the battery up all the way and the car started great. Now not so good.

Worse case I may have to do all three; Cable, starter, alternator.

I will have my Indy FD Motorsports check it out for me.

Petza914

Actually, I think the harness issue usually results in weak warm or hot starts, like after getting fuel or Starbucks. On my wife's car that had the harness issue, this is how hers behaved. Cold starts were OK.

RaidersR1

I think I found why the battery was getting low. I appears that I left a phone charger plugged into my 12v connector located in the storage area.

It was warm and obviously using juice while it was plugged in, though a phone was not plugged into it. I still have the weak start with a hot engine...but I don't believe the alternator is bad since this is not my DD the several days it sat in the garage allowed the battery to get low and appear discharged when in fact it's not.

So it's fully charged now, and starts great cold!! LOL but let's see if that truly is the issue. Most of the time I can have the car sit for a week and not have battery issues.

I know, I know..WHY is this moron allowing this car to sit for a week in the garage!! Life happens! You get busy with other things..this weekend it's off to the lake with boat so F250 has to pull the load!!

Petza914

If it's sitting for a week, it should be on a battery tender type device (Battery Tender, CTek, Porsche branded CTek). Also, you should lock the doors to put the systems to sleep and the car will then use less power while it's sitting there.

RaidersR1

I have a battery tender. Use to use it through the 12v adapter. Not sure it really charged well so I went with the alligator clips but too lazy to hook up all the time. Makes taking the car on a whim less exciting to open frunk and unhook.

I will though start locking it. Good idea there.

mreloc

You found a lake near LA with water in it?? This drought is really beginning to bum me out!

RaidersR1

There are two Brentwood's in Cali. SoCal and NorCal. I'm in NorCal. Where I'm at is an Incorporated City. SoCal is not. My town used to only have 20k in population 15 years ago. Now....I think nearing 60k.

I'm going to Don Pedro. It's got lots of water this year!!

RaidersR1

After getting the error light yet again....I stopped at my indy and the battery is NOT charging. While the engine is running the battery is only showing 12.6 on the volt meter. Now I wonder if it is just the battery cable causing this or my alternator is not charging the battery. My indy hasn't done the cable before and hasn't told me if he is willing to tackle it yet. I ordered a new alternator and will have that put in next week. Once the battery is charged and full the car does run and start ok.

I also wonder if the battery cable is also causing the alternator NOT to charge and or causing excessive draw on the battery when starting the car or while running. Just hate to pay for the cable to get done because the dealer maybe the only way to get it done...that's 1k plus for that work, plus they want to replace the started, but it sounds strong when starting.

We will see what happens after the alternator is replaced.

Petza914

He should be able to check the output at the alternator and at the battery. If it's good at the alternator, then it's almost certainly the cable. To the uninformed on these cars, the problem looks like a bad alternator, but usually isn't. My Indy says the same thing on my wife's car and I had him do the cable first and that resolved the issue. I'd you have the cable done,do the AOS at the same time, as there shouldn't be any additional labor as they go right by the same work when changing the cable. If after you do the cable, you still have the issue, then do the alternator as I think an alternator alone is about $800.