Mechanics call these paper tools tree charts or ladder diagrams.
The online auto repair manual will provide step-by-step diagnostic and troubleshooting procedures with component location diagrams for that particular failure code on that specific automobile. The best way to approach the repair of a vehicle that set a diagnostic code is to use the scanner in combination with a quality repair manual. Reading scan tool data can put you a clear path of diagnosis. Or even a stuck open thermostat not allowing the vehicle to reach its proper operating temperature. Maybe this code set because of a a stuck thermostat causing an overheating condition. In this scenario the code represents a mechanical failure in the coolant system not an electrical issue with a sensor. If we set a coolant sensor code and the voltage increases as the vehicle warms up, the sensor is working correctly.
Another example is the a temperature sensor mentioned above. I have an example about the commonly misdiagnosed O2 sensor code. More often than not the sensor is working correctly and making you aware of a problem with the vehicle. Just because the computer sets a code for a specific sensor doesn’t automatically indicate the sensor has failed. When the dreaded check engine light comes on and the vehicle sets a specific code you can then pull up the data stream for that system on the obd II automotive scanner. Reading scan tool data gives you insight on what the failure might be. If the coolant temperature and voltage remains at a fixed value, yet the vehicle continues to warm up, you may have a dead coolant temperature sensor or bad wiring between the sensor and the computer. This verifies the correct operation of the sensor and the integrity of the wiring between the computer and the sensor. Watch the coolant temperature volts rise slow and steady on the scan tool and look for problems. If the vehicle is cold you can start it up and let it run. You will be able to monitor the coolant temperature in Fahrenheit and the change in sensor voltage. You can then read the scan tool data for the coolant temperature circuit in real time. Lets say a particular automobile sets a code for a coolant temperature sensor malfunction of some kind. I have more about inexpensive scanners I own that can read the data stream at my automotive scan tool review page.
Learn how to use the scan tool data stream to identify failed components. You might also want to pull up the data stream for the sub system showing the failure and review the information in real time.
No matter what you call them, these failures are set in memory, but have not met the criteria to notify the driver by turning on the warning light. Pending codes are sometimes called history codes. If you own an advanced OBD II auto scan tool you can also check for pending codes. This confirms a hard failure or an intermittent one. It also makes sense to clear it and take a test drive to see if the light returns setting the same one.