Diagnostic trouble codes (DTCs) are the fault codes your ECU stores when it detects a problem, the same codes behind a check engine light. Connect to your vehicle (see Vehicle Connect), then open Vehicle Connect and choose Read DTC. The app reads the codes as soon as the page opens.
Each code the ECU reports is listed with:
Read DTCs reads the codes again. Export DTCs saves the list as a CSV file, diagnostic-trouble-codes.csv.
Most codes are five characters, such as P0301. The first letter is the system the code belongs to: P powertrain, C chassis, B body and U network communication.
Some ECUs report a longer code, such as P0A14-14-27. The first part is the standard five-character code, the second part is the failure type, and the third part is the status the ECU reported for the code. The description is looked up for the code with its failure type first, then for the five-character code on its own.
Clear DTCs clears every code from the ECU straight away, without asking first, and then reads the codes again. Export the list first if you want a record.
Clearing a code doesn't fix the fault behind it. If the fault is still there, the code comes back, so find and fix the cause before you clear. If the ECU doesn't confirm the clear, the app shows DTCs not cleared.
Codes are also cleared by the Complete Flash step at the end of a flash; see Flash ECU.