The implementation of OBD II diagnostics has revolutionized the way that we go about diagnosing and repairing issues with our vehicles. Those that are savvy with an OBD II scanner can now view faults that have been stored by a vehicle’s control modules, providing them with clues regarding where best to focus their diagnostic efforts.
However, like any facet of automotive repair, learning to use a scan tool proficiently takes time. One cannot simply assume that with the click of a button, the source of their vehicle’s hardship will be revealed.
Quite the contrary, you must understand the various menus and data subsets presented to you by such a device, before truly being able to make the most out of scan tool use.
Many of these menus and data subsets are listed as alphanumeric designations, which are often confused as actually diagnostic fault codes. This creates a certain amount of bewilderment among those that are new to scan tool use, often leaving one searching for what these designations mean.
Read on to learn more about various menus and data subsets encountered while using a scan tool, such as $7E8 and $7E9.
What Do Codes $7E8 and $7E9 Mean?
In all truth, designations $7E8 and $7E9 are not what one would traditionally refer to as fault codes. These alphanumeric designations are actually nothing more than menu tabs for accessing data stored on various vehicle-mounted modules.
This is perhaps best illustrated by imagining $7E8 and $7E9 as addresses that actual fault codes will be pulled from, rather than fault codes themselves.
Most major vehicle manufacturers, including Ford, Chevy, Toyota, and BMW all use designations of this type to differentiate between various modules. While some scan tools automatically pull available data from all responding control modules, others require the selection of the pertinent designation that corresponds to the module that is to be communicated with.
Therefore, $7E8 would be the selection of choice when seeking out active engine fault codes, and $7E9 would be selected to source any recorded transmission DTCs.
Related: ECM vs PCM vs TCM
Common Trouble Codes Related to $7E8
As mentioned above, $7E8 is a designation used to describe a vehicle’s engine control module. Therefore, this menu will be selected when attempting to access engine related faults. The following are several faults most commonly stored by this module.
- P0300 – P0305: Cylinder misfire
- P0171 – P0175: O2 sensor faults
- P0128: Engine coolant temperature
- P0101: MAF sensor/circuit failure
- P0411, P0440, P0442, P0446, & P0455: EVAP-related faults
Common Trouble Codes Related to $7E9
As discussed above, $7E9 is a designation used to describe a vehicle’s transmission control module. With this in mind, you will select this menu when attempting to access transmission related faults. The following are several faults most commonly stored by this module.
- P0700: Transmission control system malfunction
- P0729 – P0736: Gear ratio fault
- P0740 – P0770: Shift solenoid failure
- P0706: Transmission range sensor performance
- P0218: Transmission over-temperature.
- U0101: Lost communication with TCM
What About $7EA, $7EB, $7EC, etc.?
$7EA, $7EB, $7EC, and all other similar alphanumeric designations presented by an OBD II scan tool also serve as data subsets for specific control modules. However, these designations ($7EX), which end with a letter rather than a number, are intended to signify a particular channel of the identified controller that can be monitored.
This has little practical value, as those hoping to retrieve trouble codes from a specific module will want to select every monitored channel for that particular module. This will ensure that every stored diagnostic fault code for this module is retrieved.
Can These Codes Be Fixed?
Because of the fact that menu designations such as $7E9, $7E8, and $7EA are not actual fault codes, but rather data subsets, they cannot be cleared. Think of these alphanumeric designations as addresses, at which actual fault codes can be accessed and viewed.
When selecting these designations, you are simply stating that you would like to pull data from those particular addresses or modules.
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