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Porsche 997: Does My Car Have Alternator Cable Issues?

Early 997s have a very common issue that mimics a bad alternator. Before you start throwing parts at your car to try to fix it, follow these steps to do it once, and do it right.

By Nik Romano - March 20, 2015

This article applies to the Porsche 997 (2005-2012).

Your battery and alternator pass every test you can throw at them, yet your 997 still has a slow cranking condition, especially when the engine is already up to operating temperature. It turns out that this is an extremely common issue for early models, specifically from '05 and '06. There's a good chance the problem lies in the large gauge alternator cable, and the rest of the equipment is just fine. This how-to tells you what's involved in determining where the fault lies.

Materials Needed

  • Multimeter
  • Female Torx E-12, E-14, E-16 and Male Torx T-20
  • 1/4" and 3/8" socket sets
  • Blanket to cover rear bumper
  • Rags

Step 1 – Check battery voltage

Your issue could be as simple as a weak battery, so rule that out first.

This is a very easy thing to test. Pop open the hood, and remove the plastic cover to reveal the battery. Set your multimeter to DC Volts 20, and make sure the leads are in COM and V. With the car turned off, simply touch the leads to the two battery terminals. If it reads around 12.5V, your battery is likely in good condition and is not your issue.

Figure 1. Battery location on a 997.

Step 2 – Check alternator function

If the alternator isn't charging the system, the battery will quickly lose voltage until it will no longer be able to crank the engine.

This is just as easy as Step 1, only with the engine running. Make sure the parking brake is set and the car is in neutral or park. Once the engine is running, run the same test you did before. This time, you should see just over 14V. If the number is still the same as it was with the engine off, your alternator isn't charging the system. If the number is somewhere in between, the alternator is functioning, but there is a "voltage drop" somewhere causing it to not charge as much as it should.

Figure 2. A properly-functioning alternator will show above 14V while running.

Step 3 – Check the cables

They could be damaged, causing symptoms that look like a bad alternator.

It is a very common and very well-documented issue in early 997's. The alternator to starter motor cable isn't quite heavy-duty enough and can corrode internally or even melt. Frequently, the car will be able to start normally when cold but barely be able to crank over when at operating temperature. From underneath the car with the undertrays removed, find the starter motor on the passenger side bolted to the engine where it meets the transmisssion. Touch your multimeter leads to a good ground, and the battery + cable going from the alternator to the starter. Have a friend crank the engine. It should read no less than 12V, with the engine hot or cold, indicating that full battery voltage is making it to the starter. If you are seeing less than 12V, the cable is almost definitely the culprit.

Warning

It should go without saying that working under a hot car can be very dangerous. If you are not comfortable doing this or holding multimeter leads to parts of the car while cranking, leave it to a professional who has the experience to ensure nobody is in harm's way.

Figure 3. Badly damaged cables.

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