In today's complex automotive industry it can be difficult to test the validity of a repair that has been made. In order to judge the quality of the workmanship, one must have an understanding of a step by step technical process that is recommended to complete the repair. This information is often found in dealer supplied work orders, and can also be obtained by referencing a shop manual. Shop manuals are often published by auto manufactures and by companies such as Haynes and Chilton. In the addition to written step by step procedures one must be familiar with common shop practices. Having this both "book smarts" as well as "hands on experience" will allow a person to make an accurate determination as to weather a repair has been performed to acceptable specifications. It is important to note that repair procedures and practices can change. This is due to the fact that many replacement auto parts are often upgraded or changed in order to perform to modern standards. Also new tools are often introduced to the industry, which can change or ease the process of removing and installing replacement parts.
In today's repair industry it is not as simple as "fixed" or "still broken". In order to comprehend this you must familiarize yourself with the two ways that a mechanic diagnosis a problem that has been brought to his attention. In early model cars a mechanic would go through a process of elimination. By doing this in a systematic or checklist style fashion the mechanic would be able to pin-point the problem, and then he would move onto the steps that he would need to complete in order to repair or rectify the problem.
Due to the amount of electronic devices in modern vehicles the process is now done with an onboard computer that is built into the vehicle. This is often referred to as an OBD2 or similar device that allows a mechanic to read symptoms and problems that a vehicle has stored into its memory. These stored problems are often referred to as codes. The mechanic must use his own process of elimination in conjunction with information provided by the vehicles computer in order to determine what step needs to be taken in order to repair or rectify the problem.
Often times a vehicle will receive a new part or have a repair preformed only to find out that the computer stores another code, thus leading to another repair. This is usually due to the fact that an onboard computer cannot predict what effect the previous failing part has on the other components in the vehicle. An example of this would be if a car has a faulty oxygen sensor that is replaced, the vehicles computer cannot predict that the car ran "rich or dirty" due to the faulty part, and as a result caused a clogged catalytic converter. This is a common example of a computer not being able to predict the "cause and effect" of a previous part that has been replaced.
As a result of this many customers question the quality of work preformed on their vehicle. Many believe that their car was not repaired correctly if it has to go back and have additional repairs made. Usually it is the customers lack of understanding this complex process that that leads them to believe it was poor workmanship. This has lead to a fierce debate regarding how helpful onboard diagnostics actually are.
In conclusion, There is several ways for you to tell if quality work has not been preformed. If nothing has changed and the vehicle still displays the same symptoms it is not repaired. If the vehicle works properly, but within a very short period of operation time displays the same symptoms the problem may have been repaired but needs to have other problems addressed. If the repair in question fails due to improper installation, then the repair quality was preformed poorly.
