Why a diagnostic charge?
Many years ago when cars were somewhat basic it usually did not require much effort to determine what was causing them to malfunction. Often a visual inspection would reveal a broken part that needed replacement. Times have certainly changed, as newer cars now have become more sophisticated and dependent on computer controls to manage everything from emissions to dome lights.
Many people believe that a modern day car can be connected to a diagnostic machine that will tell us everything that is wrong with the vehicle. This is not entirely true. The reality is we do have a variety of diagnostic equipment that will communicate with the computers on your vehicle and give us valuable data to help us figure out what went wrong. Unfortunately, many times the data is vague or generic and only points us in the right direction. On 1996 and newer vehicles, the on-board computer can provide significant amounts of data, but not definitive answers. On 1995 and earlier vehicles, there is very limited data available through the computer, making it even more labor intensive to figure out what is wrong.
A thorough diagnostic service involves a variety of procedures. Generally, the first step is to connect the diagnostic scanner to the vehicle and check for any malfunction codes that are present. The technician can also look at real time data streaming from the vehicle's computer. When there is a trouble code stored in the vehicles computer, it typically indicates what area or system is malfunctioning. Armed with this information, our technician uses his years of training, experience and trouble-shooting skills to properly identify the cause of the malfunction and make recommendations on the best way to correct it. This is done by following diagnostic trouble-shooting flow charts. These flow charts indicate tests to be performed, and based upon the result, additional tests or conclusions are made. Some diagnostic flow charts are very short, others go on for several pages. The technician's knowledge and experience guide him on where to begin in the troubleshooting procedure.
Below are some examples of some of the procedures that might be used in the diagnostic process.
• Talk to customer to obtain the most information about the complaint, procure records of previous repairs.
• Drive vehicle to confirm complaint.
• Check databases to look for recalls, technical service bulletins etc.
• Visual inspection of suspected areas.
• Wiggle tests (of electrical connections).
• Connect scanner to obtain codes and or inspect data stream.
• Perform electrical and/or mechanical tests of suspect component including lab scope patterns.
• Research for information on that particular problem from places like Alldata, Mitchell, OEM Websites and the International Automotive Technicians Network database.
• Check condition of the battery and alternator.
• Perform a compression test.
• Perform a leak down test.
• Perform a vacuum test.
• Perform a cooling system pressure test.
• Perform a smoke test.
• Perform fuel pressure, quantity, and quality tests.
• Check fuel injectors fuel spray pattern.
• Perform an emission test (4 or 5 gas analyzer).
• Examine the ignition patterns on a scope or scanner.
• Check exhaust pressure.
• Check for grounds and power to components related with fault. Like relays modules etc.
• Dynamometer test.
• Consult with other techs or tech support groups if problem is an unusually difficult one.
As you can see diagnosing a car is not an easy thing today. To properly repair a vehicle, a shop must be equipped with very sophisticated and expensive equipment, subscriptions to technical information providers and most importantly very intelligent, well-educated and experienced technicians.