Driveability is a term used to describe the performance of an automobile. It relates to the ability of the car to be driven (Drive + Ability). Most of the time the term driveability is used to specifically address issues with engine performance. However, driveability can be used to describe any aspect of the automobiles performance.
In times past a simple Tune Up would cure most engine related driveability problems. However, todays engine management systems ("Computer and related sensors and actuators ") have grown in complexity and require a specific understanding of system operation along with specialized tools to accurately diagnose driveability problems.
The Diagnostic Process
Today, driveability diagnosis begins with a customer interview. The importance of this interview cannot be overlooked. It can be compared to the time spent with a persons physician describing the symptoms being experienced. Without good information diagnostics can become difficult if not impossible.
The Information gained from the customer interview guides the technician by helping to narrow down possible causes and potential components that need to be tested. After the interview the technician will try and reproduce the symptoms and verify the complaint.
Once the complaint has been verified, the technician will then search through TSB's (Technical Service Bulletins) to see if any related pattern failures are indicated.
If a relevant TSB is found the vehicle will then be tested per the TSB in order to "Prove" or "Isolate" the component responsible for the symptoms.
If no relevant TSB is found or testing from a relevant TSB fails to isolate the problem. The technician will then make a decision on which component or system he should test for problems.
Testing primarily is accomplished through understanding the operation of the system being tested along with accurate wiring diagrams and component specification. It also involves the use of specialized tools, such as: Labscopes, Digital Volt-ohm Meters, Gauges, and Scan tools.
Concerning Scan Tools, Our industry has in effect been guilty of providing the consumer with misinformation. We have unwittingly led the consumer to believe that this tool both diagnoses and fixes vehicles. Nothing could be further from the truth. In part we (the automotive service industry) have done this by either:
Trying to encapsulate the diagnostic process when talking to the consumer in order to provide a shorthand means of telling the consumer what the problem is. (ex. "I hooked your car up to the scan tool / machine and it told me you had a bad oxygen sensor, it will cost $$$ to fix your car.")
Our failure to keep up to date on emerging technologies and being content to refer the consumer to another shop or dealer that may "have the machine" to fix their car.
So, what is a scan tool and what role does it play in fixing my car?
Well, a scan tool is like a window into the operation of your cars management system. It allows the technician to get clues as to where a problem may exist. Basically, this is done through evaluating trouble codes, datastream information (values provided to the computer from sensors),and manually turning on and off actuators (ex. fuel injectors, motors, solenoids, etc.) for testing purposes.
Trouble codes appear when a sensor detects a value different from what the computer expects. These help the technician to begin pinpointing where the problem may lie. Sometimes the trouble code will identify the faulty component, sometimes it won't. It is up to the technician to determine which is the case. For example:( a vehicle may come in with a stored oxygen sensor rich code. The car may have a faulty oxygen sensor or it may not. If a fuel injector is leaking, then excess fuel will be provided to the engine beyond its current demand. In this case, the oxygen sensor is doing its job and reporting the excess fuel. Replacing the oxygen sensor will not fix this car, replacing or cleaning the fuel injector will. The computer has no means of telling us the fuel injector is at fault in this case other than reporting an oxygen sensor fault.). Did the scan tool diagnose this car... NO. Was the scan tool important in finding the problem... ABSOLUTELY.
Once the technician has found the cause of the driveability problem and the repair has been authorized and completed, a verification is performed in order to reasonably ensure the problem has been solved. If the problem has been solved the customers car is then returned.
