Lon

Well once again I seek the help of you wonderful Rennlisters. My car has an awful battery drain issue I can not find. It can drain over night. I place my multi meter between the negative cable and negative post and it reads 12.3 volts. For some strange reason I can not get an AMP reading, it just shows 0 .I have pulled each and every fuse with a test light hooked between the neg cable and post and it stayed illuminated for each pull of a fuse.

could this be releated? I know my rear blower fan runs regardless of setting on the CCU, and also the interior fan must be blowing some as well because I can feel air from the dash vents with the fan turned off and at red dot or blue dot.

I did just have a GPS unit installed right about the same time this started and logic told me it had to be the gps, well I disconnect the gps and still the same amount of draw.

So I am completley stumped.I do not know what to do next or where to start. Any suggestions?

Thanks,

Bill Gregory

If the trouble started when the GPS was wired in, there may be a connection (or lack of). And it may not be the GPS causing the problem, rather what was done to wire it in.

When you hook up your multimeter between the battery cable that you remove from the post, and the post (I use the positive terminal), you should be seeing 8ma to 20ma (that's to the right of the decimal amps). If greater than that, start with fuse 1, and pull until you find exactly what the problem is. If your fans are running all the time, that should narrow the scope of inquiry, however, I'd still go through the fuse exercise.

Colin 90 C2

I am confused by your description. The original hookup you state is for current ie.amps ...I place my multi meter between the negative cable and negative post. Voltage readiing is taken across the battery posts.

The idea of a test light is good although you can not get a quantative number. To read the drain on the battery you need to be able to read AMP.

mojorizing

Lon,
To read current , most meters require you to re-insert the leads into different connections on the meter. Also, there are protection fuses inside the meter to protect delicate circuits in the meter.

Like Colin states, you need a definitive number when your troubleshooting a current draw.


With the meter setup to read volts and in series with the load as your intial describes, you'd expect to read battery voltage.

If you have any of your fans running well after the key is removed, you got problems.

You gotta get your meter working, then your car.......

Tom W

My old meter with a 500 mA limit would not work (could not get amp info even after replacing the battery). My new meter only works when set on the 10 A scale. As mentioned, you normally have to move the connection for the leads when switching between measuring volts and amps.

My car draws 100 mA "at rest" and I've been too lazy to track it down. It only gets driven one weekend a month anyway so I leave it on a trickle charger. One day I'll get the time and ambition to fix it.

AW

mmmm... just a guess but some GPS systems have a separate antenna with its own power supply. Could it be that the GPS antenna is in fact the issue?

AW

SKM

On my '93 RS America and at least a few other 964's that I am aware of, the climate control unit failed and resulted in the same symptom - a recurring dead battery. May not be your problem but worth checking.

Lon

Thanks for the replys guys. My old multimeter couldnt measure the amps so I went and bought a new one and it read .141 amps. I pulled each fuse while watching and it did not change. For some strange reason when I opened the passenger door it dropped to .100 amp. I opened and closed the door many times after that and it made no change. I disconnected the GPS while watching and it dropped to.090. I wouldnt think that .100 should drain a battery over night , so I am wondering if have an intermittent short somewhere?

johnfm

Lon

0.141 AMps is 141 mA. The range for normal draw is 8 to 20 mA, yhats 0.008 to 0.020. So, it looks like the GPS may be the problem.

botoo

Lon, I had a similar experience and couldn't find out why the battery wouldn't start the car after only a few days. After going through the tests, and finding nothing really that could drain the battery that bad, I replaced the battery. What a difference. I found that I had a bad battery which had no cranking power left.
Something to check, anyway.

DarrylH

Same problem here, it was traced mostly to the climate control unit. My mechanic rewired it to be alive only with the ignition on, and the current draw dropped significantly. He also found some dodgy grounds (headlights) and bad a/c and oil cooler resistors (the porcelain ones in the fenders, which were about 2/3 corroded away.) There's apparently also something not quite right in the alarm system circuit, which might go along with your door position changing the current draw, and IIRC it's not wired through a regular fuse. FWIW...

Good luck

Darryl

JasonAndreas

From TSB-2706/9402; When checking current draw, if the amount is over 100mA, a relay is most likely the cause. Remove relays from the C.E.B one at a time until the current draw drops.

If current draw is over 500mA, a switch could be the cause.

If a sticking relay is suspected, proceed as follows:
- Switch the ignition on and off, remove the key and close the door.

- Install ampmeter between battery minus pole and vehicle body. Then disconnect the vehicle ground strap at the body mounting point. This will prevent interrupting the circuit and allowing the relay to collapse.

- After locating the defective relay, a higher current draw is still possible due to the control unit for the heating -A/C remaining active up to 20 minutes.

blah, blah, blah...

Maximum allowable current draw for 911 C2/4 1989-1993 = 26mA

KirkF

As mentioned in a couple of previous posts your meter has internal protection fuses. On most meters there is a separate fuse for the amp circuitry. Open the meter up and check the fuses, then proceed with your diagnosis of the power drain.

In my case its the climate control unit causing the problem, and I really havent decided what to do about it yet.

Kirk

Lon

Here is a new twist, now the Blower behind the RF wheel is cycling to a high speed and then off, over and over. Does this also tie into the CCU? I plan on sending mine to Ottos tomorrow.

JasonAndreas

I don't think Otto's Venica does the actual repair themselves, they ship the CCU to Systems Consulting. Avoid the middle man and save yourself $75 or $100USD.