Power Supply - General

Effect of disconnection or total discharge of the battery on electrical systems in the vehicle, subsequent measures:
1. Never disconnect battery with engine running.
2. Never start engine without securely connected battery.
3. Do not use a boost charger to start the engine.
4. Whenever possible, use jump leads with over voltage protection.
5. Always disconnect the battery terminals before carrying out welding work on the vehicle.
6. Wiring harness plugs of control modules or other electronic components must be connected or disconnected with the ignition off.
Exception: vehicles with the additional equipment M 536 (alarm siren with tilt sensor).

Note concerning M 536:
In order to avoid triggering the alarm siren (installed on right next to the battery) of vehicles with M 536, the battery must be disconnected with the ignition on (all loads must be switched off beforehand).

Control module memories:
Values and faults stored in the control modules can be deleted if the battery is disconnected or completely discharged.

Remedy:
If possible, all fault memories should be checked and, if necessary, printed out before the battery is disconnected.

Supply voltage fault entry:
The entry "supply voltage" could be stored in various control modules if the battery has been completely discharged.

Remedy:
Delete the "supply voltage" entry from the control modules in question.

Test drive after connecting the battery:
The fault memories of all vehicle control modules should be read out again after the test drive.

DME control module:
After disconnection of the power supply, the idle speed might change or fluctuate briefly until the idle speed positioner (M 5.2) or the throttle adjusting unit (ME 7.2) is readapted. The mixture adaptation is also lost.

Remedy:
After the battery is connected:

With the DME ME 7.2, it is necessary to carry out a learning and adaptation routine as described below:
^ Switch the ignition on for I minute without starting the engine. Do not actuate accelerator pedal.
^ Switch off ignition for at least 10 seconds.

This completes the adaptation of the throttle adjusting unit.

With all DME systems, the engine must run for several minutes before the engine control module can relearn the idle speed and mixture adaptation values.

Tiptronic:
The stored pressure adaptation values are lost if the power supply to terminal 30 is interrupted. This can result in poor shifting quality (rough shift operations) during the adaptation phase.

Remedy:
Perform a test drive. During the test drive, drive the vehicle with varying load conditions and speeds so that all shift functions (manual and automatic programs) are executed at least once. This readapts the shifting pressures of the system and thereby re-establishes smooth shifting.

Power windows:
The limit positions of the power windows are deleted from the control module when the battery is disconnected and connected.

Remedy:
Manually close each power window as far as it will go, then press the rocker switch for closing the window again. The limit position of the respective power window is now stored in the control module again.

Instrument cluster:
The trip counter is set to 0 when the power supply is disconnected.

Clock:
Depending on the software version, the clock is set to 12:00 a.m. or 1:00 a.m. when the power supply is disconnected.

Remedy:
Enter the current time again.

Note: On vehicles with PCM, 91 10 PCM position 3.

On-board computer:
Disconnection of the vehicle battery deletes the memories for average speed and average consumption. As a result, the displayed range on remaining fuel can be markedly different or even 0.
The outside temperature indicator loses its memory effect. In other words, the indicated outside temperature can be too high due to the heat radiated when the vehicle is hot.

Fuel level display:
Only 911 Carrera 4 (996) and GT3 are affected:
If the power supply is interrupted by a discharged or disconnected battery with the tank containing less than 19 liters, the calculated value for the range on remaining fuel in the instrument cluster will be incorrect or deleted.
If the tank contains less than 10 liters, it is possible that the fuel level warning light is no longer activated.
If the power supply is restored with the fuel level at less than 19 liters, it is possible that the fuel level display may subsequently display too much in some 996 Carrera 4 and GT3 vehicles.
This may lead to the vehicle breaking down.

Remedy in these vehicles:
Refill at least 19 liters of fuel; then the fuel level sensor is in operating range and its display precision is guaranteed.

Note: Refer to Service bulletins No. 9/99 "Running Out Of Fuel".

Radio:
The radio reverts to the Code function when the battery is disconnected and is thus no longer ready for operation.

Remedy:
Input the radio code. If the code card is unavailable, the radio code can be read from the DME control module (under "Vehicle data"). The code is also available from the Porsche IPAS.

PCM:
1. The PCM reverts to the Code function when the battery is disconnected and is thus no longer ready for operation.
2. When the power supply is disconnected, the built in GPS receiver loses the so-called "almanac" containing the satellite orbital paths.
3. The date and time are deleted when the battery is disconnected.
4. Radio stations stored by the customer are no longer displayed.
5. If the telephone card was inserted and the telephone was ready for operation, the telephone is subsequently disabled.

Remedy:
1. Input the PCM code. If the code card is unavailable, the PCM code can also be read from the DME control module (under "Vehicle data"). This code is also available from the Porsche IPAS.
2. Switch on the PCM with a free panoramic view for approx. 20 minutes (to load GPS almanac).
3. The date and time are also adopted once the GPS almanac has been loaded (see step 2); it may be necessary to change over to summer time (daylight-saving time). This time is transferred to the instrument cluster. If the time is then manually changed by means of the instrument cluster, this time is adopted by the PCM and synchronized with GPS time.
4. The stored stations are displayed again when station buttons 1 to 6 are pressed.
5. The telephone is enabled again when the telephone PIN code is entered with the SIM telephone card inserted.