Engine Codes $7E8 and $7E9
Learning how to use an OBD-II scanner properly takes time and experience. What appears on your scanner as codes $7E8 and $7E9 are not actually diagnostic trouble codes, but rather a subset of data that must be understood to be interpreted.
This can be confusing for those new to diagnostic tools. Keep reading to learn about the different menus and data subgroups like $7E8 and $7E9 that you may see when using a diagnostic tool.
What do codes $7E8 and $7E9 mean? In reality, the designations $7E8 and $7E9 are not what would traditionally be considered error codes. These alphanumeric designations are actually just menu tabs that access data stored in various modules installed in your vehicle. Perhaps the best way to explain this is to think of $7E8 and $7E9 as addresses from which the actual error codes are retrieved, rather than the error codes themselves.
Most major automakers, including Ford, Chevrolet, Toyota, and BMW, use this type of designation to differentiate between various modules. Some diagnostic tools automatically retrieve the data available from all control modules that respond, while others require you to select the appropriate label that corresponds to the module you want to communicate with. The $7E8 designation typically corresponds to the vehicle’s Engine Control Module (ECM), while the $7E9 designation refers to the vehicle’s Transmission Control Module (TCM).
So, $7E8 would be the first choice if you were looking for active engine trouble codes, and $7E9 would be selected to look for all recorded transmission DTCs.
Common Error Codes Associated with $7E8
As mentioned earlier, $7E8 is the designation used to represent the vehicle’s Engine Control Module. Therefore, this menu is selected when attempting to access engine-related errors. Below are some of the most commonly stored errors by this module:
P0300 – P0305: Cylinder misfire
P0171 – P0175: O2 sensor error
P0128: Engine coolant temperature
P0101: MAF sensor/circuit error
P0411, P0440, P0442, P0446, and P0455: EVAP related errors
Common error codes related to $7E9
As explained above, $7E9 is the name used to represent the vehicle’s transmission control module. With this in mind, select this menu when trying to access gearbox related errors. Below are some of the most commonly stored errors by this module:
P0700: Transmission Control System Failure
P0729 – P0736: Conversion Error
P0740 – P0770: Switch Solenoid Switch Failure
P0706: Transmission Range Sensor Performance
P0218: Transmission Overheating.
U0101: Communication with TCM Lost
What about $7EA, $7EB, $7EC, etc.?
The $7EA, $7EB, $7EC, and other similar alphanumeric designations displayed by OBD-II diagnostic tools also serve as data subsets for a particular control module. However, these designations ($7EX), which end with a letter rather than a number, are intended to identify a particular channel on the identified controller that can be monitored.
This has little practical value, since if you want to retrieve trouble codes from a particular module, you must select each of the monitored channels on that particular module. This ensures that you retrieve all diagnostic trouble codes stored on that module.