OBD-II Trouble Code Technical Description
The code indicates that there is a detected slip in the transmission friction element D.
What does that mean?
This is a generic powertrain diagnostic trouble code (DTC) that applies to OBD-II vehicles with automatic transmissions. This includes vehicles from various manufacturers such as Chevrolet, GMC, Toyota, VW, Ford, Honda, Dodge, Chrysler, etc. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
The description of “transmission friction element” is quite vague considering the multiple friction elements involved in the mechanical operation of an automatic transmission (A/T). It’s important to note that manual transmissions also use similar friction materials, such as clutches.
In this case, it is likely referring to an A/T. The symptoms and causes can vary significantly depending on various factors, but it is crucial to consider the overall health of the automatic transmission and the Automatic Transmission Fluid (ATF) as the first step.
Problems with the internal friction materials in the A/T can lead to erratic driving conditions, including issues with shift timing, torque output, and other consequences related to this fault. Factors such as abnormally paired or inadequately inflated tires can cause internal slippage due to their unsymmetrical circumstances. Therefore, it is important to consider the functionality of the drivetrain and troubleshoot any faults, keeping in mind even minor differences in tires can indirectly cause issues like this.
When the ECM (Engine Control Module) activates this P079D code and related codes, it proactively monitors and adjusts other sensors and systems to ensure proper self-diagnosis. Therefore, it is crucial to address this issue before it potentially leads to further problems. While it may be a simple fix, it could also indicate a complex internal electrical malfunction, such as a short, open circuit, or water intrusion. It is advisable to seek appropriate help, as even professionals can make easily overlooked mistakes that can be costly.
The letter “D” in this case may refer to a specific circuit/wire or a specific friction element within the transmission. It is always recommended to refer to the service manual for specific locations, distinctions, and other specifications.
Code P079D is logged by the ECM when it detects slip in the internal “D” friction element inside the transmission.
What is the severity of this DTC?
As mentioned earlier, it is not advisable to leave this issue unattended, especially if you are actively using the vehicle with the fault(s) present. It should be prioritized, especially if the vehicle is used daily.
Photo and cutaway of an automatic transmission:
What are some of the symptoms of the code?
Symptoms of a P079D trouble code may include:
What are some of the common causes of the code?
Causes for this P079D friction element slip code may include:
What are some P079D troubleshooting steps?
The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins for known issues with the specific vehicle.
Advanced diagnostic steps become very vehicle specific and may require the appropriate advanced equipment and knowledge to perform accurately. We include basic steps below but refer to a vehicle year/make/model/powertrain specific repair guide for specific steps for your vehicle.
Basic Step #1
It is crucial to follow basic maintenance procedures for the transmission’s health. Start by checking the cleanliness and debris-free condition of the ATF (Automatic Transmission Fluid). It is also important to adhere to proper maintenance schedules to prevent future faults. If you don’t remember the last transmission service (i.e. filter+fluid+gasket), it is recommended to perform this service before proceeding. There may be debris trapped internally in the oil, and a simple service might resolve the issue. Make sure to use the correct ATF for your specific make and model.
Basic Step #2
When trying to locate the connector/harness for this system, you may need to find a junction connector. There may be one “master” connector, so refer to your manual to ensure you are working with the correct one. Ensure that the connector is properly seated to establish a good electrical connection. The location of the connector on the A/T may subject it to vibrations that could loosen connections or cause physical damage. Additionally, there is a possibility of ATF saturating connectors and wires, leading to present or future issues.
Basic Step #3
It is always wise to consider the overall condition of your vehicle, as other systems can directly affect the transmission and vice versa. Uneven tires, worn-out suspension parts, and incorrect wheels can cause issues in this system and possibly others as well. Therefore, it is important to address any imbalances to potentially resolve this code.
This article is strictly for informational purposes, and the technical data and service bulletins specific to your vehicle should always take precedence.
