OK boyz, good luck with this one...

'01 C2 w/ approx 72K miles. Seems to crank slowly, like battery voltage is low (though I don't have another 996 to compare it to). While driving the lock light on the dash will light and then go out randomly. If I push the lock button the interior lights will come on for a second and then go out (while driving). When I unlock the door with the key fob, and open the door the horn will beeb twice (which it never did before). I'm assuming all these issues are connected because they all started at the same time. I had the battery and alternator teststed today and they are a-OK.

Thoughts?

 

Four things to check: ignition switch going bad (most likely), battery getting low, alternator/alternator voltage regulator going bad. While you are at it, replace the headlight switch too as it seems to have same life span as the ignition switch.

 

Bad/corroded ground, or grounds around the dash area, or the large ground strap between engine and chassis.

 

How's your instrument cluster voltmeter reading? Normal behavior is key on engine off ~12v then it goes down to ~10v when cranking. Once engine is running, it should be back at ~14v. Then as you drive the car, it should taper to 13.5-14v at all times.

 

Looking on ECS.com, ignition switches are relatively cheap, so willing to try replacing that as a troubleshoot. There are like 12 listed... Any reccomendations on brand?

Dash voltmeter reads normal w/ engine off & while cranking/running.

 

It sounds more like to me something is wrong with your alarm/immobilizer unit. Any water under the passenger seat? Do you have access to Durametric to scan the car? Maybe you can disconnect the battery and then re-seat and check the immobilizer connectors. Spray the pins with Deoxit.

 

For slow cranking go to the passenger side of your engine compartment and look way forward, you'll see a Pos battery terminal block ( I believe it's almost above the tranny), check this for corrosion then follow it back to the middle of the aft engine and check this too.

 

For slow cranking, it's also possible the starter/alternator "Y" cable is bad (very common). You can try this test. When car is running, turn on the a/c, low beam, and the rear defroster. If the cluster voltmeter reads below 13.5v, most likely that cable (or the alternator) is bad. To be 100% sure you need to do a voltage drop test on the cable (between the alternator and the battery "+" jump post above the a/c compressor).

 

OK, so after some additional online research, I think Ahsai hit the nail on the head. I think my problem is around the alarm/central locking. I've noticed that my passenger door window lowers sporadically (sometimes not at all) with opening the door.

To remedy that problem, do I need to replace the latch? I've also read that I can simply replace a micro switch? I'll start with this to see if it addresses my problem.

 

Don't forget to swap out the electrical portion of the ignition switch. I would do this first and just consider it "preventative maintenance". It will fail at some point anyway, so go to NAPA, spend the $12 to buy the switch (heck, spend $24 and buy two and throw the extra in your door pocket "just in case") then spend 20 minutes swapping it out. It might not fix your problems, but with any electrical gremlins, that's what I'd start with since a bad ignition switch will affect so much of the electrical system. To start by tearing into other parts of the electrical system chasing the gremlins would be like having your dome light burned out and deciding to replace the alternator, battery, wiring harnes, etc without first swapping out the $2 light bulb.

 

Agreed with the ignition switch recommendations. I had all kinds of weird crap happen when mine went out.

 

Just in case anyone follows up on this thread & needs an answer.

I believe the slow cranking is a separate issue. I replaced the passenger door latch with a used unit for approx $50 and it fixed the window not dropping issue + the lock indicator on the dash. Problem solved.

 

The doors locking on their own, the horn sounding when locking the car, the inconsistent passenger window behavior (not dropping when the door was opened or worse dropping when it was opened but going back up again afterwards) were all due to a bad passenger door lock assembly. This is a rather fancy black plastic thing that has some smarts in it.

The only times (two) I have had slow cranking with my 996 Turbo at some point not too long after this first started the battery went flat. The charging system was fine, just a worn out battery in one case, and the second proved to be a just a bum (short lived) battery. The thing last barely 7 months from brand new to flat.