Introduction
The Carrera from 99 onward has become one of the most technologically advanced vehicles with a considerable amount of electrical and electronic systems than ever before. Attempting to diagnose these newer vehicles requires the knowledge of how the various systems work and interact with each other. The correct diagnosis is always backed by knowledge.
Porsche is one of the most secretive of the automotive manufactures when it comes to technical data. I believe that it is this lack of information, that Independent repair facilities would rather not work on these vehicles.
Diagnosis should always start off by duplicating the concern, that is to say the actual problem. It can become very difficult and time consuming to try and troubleshoot a problem that is intermittent. If your problem is intermittent there are still ways to test and figure out the root cause of failure. Obviously in a real world situation most problems with cars are of the intermittent nature.
It is always good to know the repair history of the vehicle, it might be that someone recently tried to install a radio, or the body shop worked on the vehicle. Many times it is outside influence that causes electrical problems or check engine light illumination.
A logical approach to diagnosis will always be the easiest way to fix a problem. More often than not problem diagnosis can be time consuming and frustrating. However, the task at hand will be much more easier if you apply a methodical troubleshooting strategy. Always remember that information is what will help you diagnose and fix a car, it’s not magic, its all about knowing how a particular tool can aid you in testing, understanding what sensor output values really mean, what voltages, amps, resistance are normal or not. The following will outline a basic approach to diagnostic troubleshooting that will ensure that you do not overlook the needed information for a successful diagnosis.
Diagnostic Approach
1.Verify the Complaint Concern Identify all of the suspected symptoms. Confirm the actual presence of the symptoms. Verify under what conditions such as road speed, load, transmission gear, temp ect. Test drive the vehicle.
2. Analyze the problem Begin to determine the possible causes of the fault. Always look at the vehicles repair history if it is possible.
Determine What controls the faulty function.
Determine if the failure is a multiplexed network related component, is it an input or output problem.
If a scan tool is available then you should go ahead and check for fault codes. If there are fault codes stored you should write them down for later reference. Determine what systems or part of a system should be tested.
Always try and compare test values or conditions with a know good similar model. At this point you should have narrowed down the problem to a certain area of the car.
Determine the data messages that control the function and establish which modules or sensors transmit the data and which modules use the data.
If a Bi-directional scan tool is available, ( Bi-directional means a scan tool that can force a component or system to operate at the push of a button on scan tool) perform an activation test of the system or component. This will allow you to determine if you have a computer command problem, wiring issue or component issue.
3. Inspect, test and pinpoint the fault.
Always visually inspect the vehicle and look for obvious faults that could contribute to your problem at hand.
You should begin to determine what test equipment you will want to use, Dvom, Scan tool, DSO ( Digital storage oscilloscope), fuel pressure gauge ect.
Gather all pertinent technical information, such as wiring diagrams, technical reference books ect.
• Test the system or component that is suspected as faulty. • Always try and test circuits and components in a logical sequence. • Start testing the circuit or component that is most likely the cause and the easiest to access. •
Most intermittent problems are very difficult to isolate and replicate. You can perform wiggle tests of the wiring of the suspected system/s or component/s.
Use a heat gun to recreate a hot condition on wiring or a component.
Use a can of Lighter fluid propane, the spray will be extremely cold, this will allow you to recreate a cold condition on the component or wiring.
Never guess, as this will only get expensive in the long run. Keep an open mind, could the problem be caused by another circuit or system or component.
Never stop your engine performance or electrical diagnostic testing until you have found the root cause of the failure.
4. Perform the repair • Always follow the recommended service repair procedures indicated by the OEM.
There will be times were the replacement of a component will require a special activation sequence or specific (coding) that gives a component or control unit the right instructions on how to operate.
Confirm that the wiring, connector/s, ground points and power supplies are in proper working conditions.
If they are not, you run the risk of having a repeat repair failure. • Replace the defective component or repair the defective wiring or connector. • With the engine management system, after a repair you will need to erase the fault code.
If you had a Fuel supply or adaptation fault code, oxygen sensor code, misfire code, or a bad mass air flow sensor, you will need to reset the adaptation in the DME.
This will reset the fuel adjustment maps to there base levels and will also reset the misfire adaptation maps as well.
Perform complete adaptation of E-throttle, fuel adaptation and misfire adaptations.