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my car is losing power is it battery or alternator?


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I started my 2002 911 C4 after a long cold winter and it started first try. I then drove it for 25 minutes to recharge things stopped for 10 minutes then went to start it again and it wouldn't start. It first went click, click, click, click, click when I turned the ibnition. I then tried again and nothing. I waited 4 hours and tried again and it started, I drove it for 10 minutes and the battery gauge was slowly going down and lights on the dash were shutting down. The computer indicated to take it to a garage, PSM problem and ABS problem both indicated by the computer.

WHat is wrong with my new baby. I have only had it for 6 months and it was garaged for 4 monrhs.

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I would start by disconnecting & giving your battery a good charge with a battery charger (not a maintainer) for at least 12-14 hours. Your winter hibernation may have been the final straw especially if the battery is 4 years or older. If you disconnect the battery, make sure you read your handbook,re: have the radio code and don't close the front hood.

If you have a multi-meter, you can do a rough check if your alternator is working. After fully charging your battery, wait a few minutes and you should have at least 12.6 v at the battery terminals. Anything less and its a faulty battery.

If OK, you then connect the battery & run the engine, you should have between 13.8 v and 14.3 v at the battery terminals. This indicates the alternator is charging.

This is not a perfect system test (it really needs load testing), but it will give you some idea of the alternator's ability....

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I tell you now , it will more than likely be the diode pack on the alternator( Rectifier). Very common fault. Reads good voltage when starting the engine from cold, but slowly as you drive, normally 30 minutes< the voltage drops.

Check the voltage when the engine is warm. Cold might be 13.5 but as it warms could drop as low as 10 V. Thats when the world falls apart and all the alarms come on.

Frank

Edited by Sunnyside
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I started my 2002 911 C4 after a long cold winter and it started first try. I then drove it for 25 minutes to recharge things stopped for 10 minutes then went to start it again and it wouldn't start. It first went click, click, click, click, click when I turned the ibnition. I then tried again and nothing. I waited 4 hours and tried again and it started, I drove it for 10 minutes and the battery gauge was slowly going down and lights on the dash were shutting down. The computer indicated to take it to a garage, PSM problem and ABS problem both indicated by the computer.

WHat is wrong with my new baby. I have only had it for 6 months and it was garaged for 4 monrhs.

That is your alternator failing. PSM and ABS turn off when there is not enough charge in the car.

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If your battery is at fault the replacement is a simple process. But the alternator and also the voltage regulator replacement can also be done and there is some DIY out there. Here's the links for some of them Alternator replacement , and the regulator which is really easy to do regulator replacement also good info here Regulator replacement 2....

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Just fixed this same problem on mine it was easy breezy! The problem is with the regulator on the back of the alternator. This job was extremely simple to do and only cost me a total of $36 to fix. I actually finished mine yesterday, it took me all of an hour or so. Here's a link with all of the information and the DIY. http://forums.pelicanparts.com/porsche-996-997-forum/408495-alternator-repair-regulator-replacement.html

Apparently what happens is the alternator gets hot as it warms up and the regulator is not doing its job anymore so when you first start the car the voltage is great, but is slowly goes down when the car gets warmed up. Mine now holds strong at 14v, all day long.

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So, are you guys saying that when the alternator diode pack or regulator fails, the dash mounted charge light does NOT illuminate indicating a faulty charging circuit ??

Usually this warning light illuminates when the charge voltage is less than the battery voltage.....which is exactly whats happening.

Or am I missing something?

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So, are you guys saying that when the alternator diode pack or regulator fails, the dash mounted charge light does NOT illuminate indicating a faulty charging circuit ??

Usually this warning light illuminates when the charge voltage is less than the battery voltage.....which is exactly whats happening.

Or am I missing something?

Exactly, thats why its a pain in the ar*e fault when you first get it. In-fact , because the regulator will work for a while whilst the engine and alternator are cold it makes diagnosis very hard. But rest assured,when the diode pack fails you dont get the red charge light on the dash.

Frank

Edited by Sunnyside
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So, are you guys saying that when the alternator diode pack or regulator fails, the dash mounted charge light does NOT illuminate indicating a faulty charging circuit ??

Usually this warning light illuminates when the charge voltage is less than the battery voltage.....which is exactly whats happening.

Or am I missing something?

Exactly, thats why its a pain in the ar*e fault when you first get it. In-fact , because the regulator will work for a while whilst the engine and alternator are cold it makes diagnosis very hard. But rest assured,when the diode pack fails you dont get the red charge light on the dash.

Frank

Thank you to all who responded to my question. I just joined Renntech and am already a big fan.

You were right. I took it into a local Porsche repair shop and it is the alternator. I am unsure if it was the voltage regulator or what part of the alternator. He charged me $600 which I thought was a great price until I heard from another comment that I may have been able to do it for $36 and one hour of my time. I am not that mechanically inclined so I am OK with the bill as long as baby is working again. It is spring time in Toronto Canada and driving season is amongst us!!!! Thanks again

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If it's fixed don't sweat it. Do you still have the old alternator? If not go back to the shop and see if you can get it and just pay the core charge because chances are that's a good alternator that would be an awesome spare. When you get it back just take a couple of nuts and screws off the back and switch out the regulator and your back in business with a good alternator to spare.

Congrats on getting back on the road. Don't be afraid to work on your car, that's what ownership on these things are all about. Push come to shove, get someone to fix it after you tried, lol. These cars despite how they look have been pretty easy to work on.

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Sunnyside has it nailed:

"I tell you now , it will more than likely be the diode pack on the alternator( Rectifier). Very common fault. Reads good voltage when starting the engine from cold, but slowly as you drive, normally 30 minutes< the voltage drops.

Check the voltage when the engine is warm. Cold might be 13.5 but as it warms could drop as low as 10 V. Thats when the world falls apart and all the alarms come on."

My experience was with my MY03 Boxster. Because I have a Carrera instrument cluster, I have the voltmeter. For the past week or so, I noticed the voltage dropping - sometimes as low as 10.5 volts indicated - as I drove along. At the point that the maximum voltage (after the car sat overnight and following a start) never exceeded 12 volts, I measured alternetor voltage with a digital voltmeter. The cool alternator voltage was now barely 11.5 volts.

Suspecting the voltage regulator, I dropped the car off at the dealer. The technician confirmed only that the alternator was not charging properly. Seeing how the cost of a new alternator is in excess of $1100 and there is no "official" protocol for repairing bad alternators, I asked the technician to remove the alternator so I could take it to a repair facility in the neighborhood. The long and the short of the story is that I had a repair facility replace the (indeed) bad voltage regulator and had the technician reinstall the alternator. The bill for the entire job was $84 for the alternator repair and two hours shop time (less a 10% PCA discount) for a total of about $290.

While not a primary scan instrument, the voltmeter should be eye-balled periodically to see if any bad trends are developing. A failing voltage regulator could explain why some people go through batteries quickly. For the Boxster owners who would like to monitor their charging system, Pedro of Pedro's Garage sells a voltmeter kit. The display is mounted on the fuse panel cover. I have no affiliation with Pedro's Garage, nor am I a customer....satisfied or otherwise.

Bill

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Another good tip is if you suspect the alternator, take it to your local auto parts store.

Most reputable and trustworthy stores can bench test it in a few minutes and tell you if you need a new one.

Some will even give you a nifty print out showing you how it performed.

It is pretty easy to remove the alternator on the 996... just a few bolts and some elbow grease.

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