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1999 Porsche 911 Question: Electical probelm

 

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Agee11, Huntington Beach, CA, April 14, 2011, 09:50
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Let me start by saying that the volt meter in car spiked at over 16 volts. at this time lighter works, red light on radio works but nothing else. Checked all fuses all look good. Anyone have any other ideas??? Worried might have fried computer not sure. Is there a test or something im missing please help... 911 Cab. 996, 1999 manuel

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    April 14, 2011, 17:57
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     Master

    The damage to the DME (computer) is possible, but you really need to see a Porsche specialty shop with a PIWIS diagnostic capability to scan all the systems.
    Did you get a car wash or detailing right before this happened?

    Zee

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    Agee11, April 14, 2011, 18:24
     Rookie

    Thanks for the reply. To answer your question about the car wash or detail the answer is no. Problem started with the volt meter in car reading appox 11 volts then car went dead. Had to jump start and problem went away. This morning started it backed out of drive way and noticed volts at 16 and above, pulled back into garage let sit for a hr or so tried to start everything dead, no lights, no nothing. What is a DME and is it expensive??

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    ZeeTech, April 14, 2011, 18:49
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     Master

    Looks like the voltage regulator failed, which is part of the alternator. Under / over voltage could cause permanent damage for control modules, they are sensitive electronics.
    The DME, Digital Motor Electronics - is the engine control computer, however there are many other computers also. These parts are all expensive, so you really don't want to just guess.
    Even the cost of a new alternator is near $1600 + labor.
    I hope the ignition key was out or in the OFF position when you jump started it. Sudden spike could also damage electronics.
    The reason for my question about the car wash / detailing is because many alternator gets damaged when soaked in water.

    Here is some info on the electronic system of the 911's:
    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.

    Zee

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