terrellda

I am currently troubleshooting an electrical problem in my 2001 Porsche C4. No aftermarket items have been added to vehicle. Within 2-3 days the battery dies regardless if I drive it everyday.

Here is what I have done so far:

1. Battery disconnected, charged on battery tender, then left disconnected from vehicle for 4 days battery Voltage remains at 12.68 v. Battery has also been load tested at local autoparts store, both out of vehicle and installed with vehicle running.

2. Charging system with car running maintains over 14 v on dash gauge no fluctuation with RPM change. Charging system has been systematically excluded by removing the alternator completely and disconnecting the starter wiring harness. Battery still drains within 2-3 days down to 10.34 v. Then charged battery. (these 2 Items still disconnected/left out of car)

3. Fuse block in driver's foot well, each fuse removed 1 at a time and verified for continuity and for amperage draw by connecting Multi Meter in series with negative battery cable. Amperage draw is 0.017 A.

4. Removed all relays in driver's foot well, battery no longer drains, stays at 12.68 v for 3 days. Reinstalled top row of relays, 2 days no voltage drop, reinstalled 2nd row of relays, 2 more days no voltage drop. Reinstall 3rd row, 1 day voltage at 10.68 v. removed 3rd row relays and charged battery. Installed 4th row relays, 2 more days no voltage drop. Installed 3rd row relay #12, 2 days no voltage drop. Installed relay #13, voltage drop within 1 day. Removed relay 13 charged battery and installed relay #16 , 2 days no voltage drop.

5. Issue narrowed down to fuel pump system #13 relay. So I disconnected 4 wire plug at fuel pump and reinstalled #13 relay and voltage dropped after 1 day. Fuel pump eliminated from system.

So I have been searching for the wiring diagrams to see where else this #13 relay goes to. If anyone can assist me in finalizing this electrical problem I would be very grateful.

Ahsai

Interesting problem. Some questions:

- You had to wait for days between testing because the drain will not show up even half an hr after locking the car but somehow it will occur when you were not looking in those two days? It's a lot easier if you can detect the drain when it's happening.

- You said 0.017A drain, was that with all fuses and relays INSTALLED?

Pin out of relay #13 here:
30 ---> fuse C4 ---> battery (hot at all times)
85 ---> DME socket IV pin 10 (fuel pump relay)
86 ---> "+" power supply from the MF+DI relay (switched power)
87 ---> fuel pump

Have you bench tested relay #13 and checked none of the pins are shorted to each other (except between pin 85 and 86 should have some resistance like a hundred ohms).

targa996

Yep - I'd start by replacing that relay with a new one ...

terrellda

#13 relay has been replaced. Both relays measure on average 61.4-62.0 ohms across pin 85 and 86.
Removed C4 fuse and #13 relay. Measured voltage at fuse C4, bottom contact - 12.61v (same as battery voltage) Continuity verified from top of fuse C4 contact to pin 30 of #13 relay slot. Reinstalled fuse C4.
Voltage at pin 30 is 12.57v
Voltages with ignition switch off at pins 85 and 86 are 0v.
With ignition on voltage at Pin 85 is 3.64v and Pin 86 is 12.55v
However there are some instances where the voltages remained at pins 85 and 86 after the ignition was turned off.

Where are the other 2 relays located? (MF+DI and DME) Maybe these relays are sticking closed intermittently.

Question: Should I have continuity between pin 87 and ground? I want to say yes because the power will always be flowing to ground. This should not cause a battery drain matter due to the relay not being energized when the ignition is off.

***I used the Battery negative post for all of my voltage checks

Ahsai

Pin 85 connects to the DME directly so there's no relay in between. The DME provides ground to this pin to activate the relay/fuel pump.

The MFDI relay is the top left relay (position #1) behind the rear seat panel.

Pin 87 connects to the fuel pump, which then connects to the ground. So you should see very low resistance between pin 87 and the ground.

terrellda

Do you have the wiring layout for the MF+DI relay?

Ahsai

This should be good enough http://www.ganino.com/games/Porsche%...01999-2000.pdf

Since yours is a C4, use sheets 18 and 19 and ignore sheet 12. The MFI+DI relay is in sheet 19.

terrellda

Thank you Ahsai, I really needed the wiring diagrams. It is so difficult to troubleshoot wiring without a diagram.

I removed the #1 relay for the MF+DI: Continuity/resistance for pin 85-86 was 70.1ohms and the other pins were not shorted. I went ahead and replaced the relay regardless.

Now, I will wait again to verify voltage drop.

Ahsai

Just curious why you are not following the normal power drain troubleshooting where you connect a multimeter in series to the battery cable and measure the current drawn? Why wait for days for v drop in the battery? I can't imagine swappng out a component then wait for days to infer if that's the fix...I guess you must have your reasons.

terrellda

I did all of the normal power drain checks as stated in original post.

After all of the troubleshooting and grey hair caused by this issue. I decided to go back to the Auto Parts store and have the battery checked again. Go figure, after they placed it on a quick charge, the Battery tested bad for a dead cell.

Do a lot of people have issues with the AGM batterys? This one was only 1 year old.

Ahsai

So the new battery fixed the problem?