Effect Of Disconnection Or Total Discharge Of Battery On Electrical Systems In The Vehicle And The Precautions To Be Taken
Information
Control unit memories
Values and faults stored in the control units can be deleted if the battery is disconnected or completely discharged.
- If possible, all fault memories should be checked and, if necessary, printed out before the battery is disconnected.
Information
Supply voltage fault entry
The entry "supply voltage" may be stored in various control units if the battery has been completely discharged.
- Delete the "supply voltage" entry from the control units in question.
Information
Ready status
In some countries (presently the U.S.A. and Canada), after disconnecting the battery, it is necessary to reach the Ready status by a test drive and/or by using the Porsche System Tester DME control module menu). If in doubt about this, contact the relevant importer.
Information
2470 DME control module
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!
After disconnection of the power supply, the idle speed might change or fluctuate briefly until the throttle valve adjusting unit has been readapted.
The mixture adaptation is also lost.
After the battery is connected:
With the DME, it is necessary to carry out a learning and adaptation routine as described below:
- Switch ignition on for 30 seconds without starting the engine.
- Do not actuate accelerator pedal.
This completes the adaptation of the throttle valve adjusting unit.
Information
Tyre pressure monitoring system
When the battery is disconnected and connected, the tire pressure is first displayed as "- - -".
- Once the battery has been disconnected and work is complete, the vehicle must be driven for a short distance.
The actual pressures will then be displayed again.
Information
4560 Steering angle sensor
The steering angle sensor must be reinitializes when the battery is disconnected and connected.
- Turn wheels to straight-ahead position.
- Switch ignition off and then on again twice.
- Start engine.
- From the straight-ahead position, turn steering wheel approx. 20° to the right, past the straight-ahead position.
- Drive the vehicle straight ahead for at least one second at a speed above 4 km/h (2.5 mph).
The steering angle sensor segment is recognized again in this process.
Once the sensor has been successfully initialized, the fault code that is stored in the fault memory is documented using the fault deletion counter.
The fault memory erases itself automatically.
The PSM indicator light in the instrument cluster goes out.
Information
Motor for sunroof
The limit positions of the sunroof are deleted from the control unit when the battery is disconnected and connected.
- Switch on ignition.
- Press the rocker switch to open until the sunroof is completely open.
- Press the rocker switch to close until the sunroof is completely closed.
- Touch the one-touch function and check if the sunroof is in the end position for "optimal noise level". If not, then repeat the process.
The end positions of the sunroof are now stored in the control unit again.
Information
Sun blind motor
The end positions of the sun blind are deleted from the control unit when the battery is disconnected and connected.
The sliding roof must be closed fully in order to standardize the roll-up sun blind motor.
- Switch on ignition.
- Press the rocker switch to open until the roll-up sun blind is completely open.
- Press the rocker switch to close until the roll-up sun blind is completely closed.
- Touch the one-touch function and check whether the roll-up sun blind moves to its end position. If not, then repeat the process.
The end positions of the roll-up sun blind are now stored in the control unit again.
Information
6452 Power windows
The end positions of the power windows are deleted from the control unit when the battery is disconnected and connected.
Perform the following procedure for all power windows:
- Close the doors.
- Actuate rocker switch and fully close window once.
- Actuate rocker switch once more to close.
The upper end position of the window is stored.
- Actuate rocker switch and fully open window once.
- Actuate rocker switch once more to open.
The lower end position of the window is stored.
Information
9025 Instrument cluster
Clock
The time is deleted when the power supply is disconnected.
- Select "Time" under "Vehicle", "Settings", "Date & Time" in the on-board computer menu.
- Tick Select GPS Time .
- The evaluation of the GPS time from PCM is used as the time.
Trip counter
- The trip meter is set to 0 when the power supply is disconnected.
Information
Airbag control module
If the battery is disconnected for less than 100 seconds when the ignition is switched on, a CAN time fault, which makes diagnosis of the airbag control unit impossible, may be stored in the airbag control unit.
- Removing the ignition key erases the fault.
Information
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 display 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.
Test drive after disconnecting battery
Information
Depending on the vehicle equipment fitted, all these work steps are carried out during the test drive.
Read out the fault memories of all control units after the test drive.
- If there is a fault present, check to see if the fault was caused by an undervoltage.
- If faults were caused by an undervoltage (or CAN timeout error), erase the fault memory, perform another test drive and read out the fault memory.
- If faults were not caused by an undervoltage, correct the faults in accordance with GFF (Guided Fault Finding).