What Does It Mean?
This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles with an automatic transmission. This may include, but is not limited to, vehicles from Chevrolet, GMC, Toyota, VW, Ford, Honda, Dodge, Chrysler, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
Transmission friction element. A rather vague description given that there are many friction elements involved when considering the mechanical operation of an automatic transmission (A/T). Not to mention manual transmissions also use similar friction materials (i.e., clutch).
In this case, I suspect we are talking about an A/T. Symptoms and causes vary significantly depending on many things, but it is important to note that the first thing to consider is the overall health of the automatic transmission and particularly your ATF (Automatic Transmission Fluid).
Problems with the internal friction materials in the A/T will most likely lead to erratic driving conditions regarding shift timing, torque output, among countless other consequences of this fault. Abnormally matched tires, underinflated tires, things of that nature tend to cause internal slipping given the asymmetric circumstances. That being said, keep this in mind when examining transmission functionality and troubleshooting faults. Installed a recently used tire? Same size? Check the tire sidewall to verify. Sometimes minor differences can cause indirect issues like this.
Typically, when the ECM (Engine Control Module) activates this P079B code and related codes, it monitors and proactively adjusts other sensors and systems to ensure proper self-diagnosis. So, rest assured, you need to resolve this issue before your daily driving needs consequently cause other potential problems. This could be a simple fix, certainly possible. That said, it could also be a complex internal electrical malfunction (i.e., short, open, water intrusion). Make sure to get help accordingly here, even pros make easily overlooked mistakes that cost thousands, speaking from experience here.
In this case, the letter “B” may refer to a few different possible distinctions. You could be facing a specific circuit/wire or a specific friction element within the transmission. That said, always refer to your service manual for specific locations, distinctions, and other specifications.
The P079B code is logged by the ECM when it detects slippage in the internal friction element “B” inside the transmission.
How severe is this DTC?
As explained earlier, this is not something I would leave unattended, especially if you are actively using the vehicle with the aforementioned faults. You absolutely should prioritize this. Well, if driving your vehicle is a necessity, every day.
What are some of the symptoms of the code?
Symptoms of a P079B trouble code may include:
Uneven handling
Transmission slipping
Irregular shifting
Abnormal shifting patterns
Harsh shift selection
ATF (Automatic Transmission Fluid) leak
Low torque
Abnormal power output
What are some common causes of the code?
Causes
of this P079B friction element slippage code may include:
Low ATF
Worn friction element (internal)
Dirty ATF causes
Wiring issue (e.g., open, short, chafing, heat damage)
Uneven tire dimensions
Issue causing uneven rotational speed/circumference (e.g., low tire pressure, stuck brake, etc.)
TCM (Transmission Control Module) problem
ECM (Engine Control Module) problem
Water damage to the module and/or harness
What are the troubleshooting steps for P079B?
The first step in the troubleshooting process for any malfunction is to search 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 operate accurately. We include the basic steps below, but refer to a year/make/model/powertrain-specific repair guide for steps specific to your vehicle.
Basic Step #1
It is imperative that you follow basic maintenance procedures accordingly at this point; regarding transmission health, start with the fluid. Your ATF (Automatic Transmission Fluid) must be clean, free of debris, and also, proper maintenance schedules should be followed to prevent further failures like this in the future. If you don’t remember the last time the transmission was serviced (i.e., filter + fluid + gasket), it’s a good idea to proceed before continuing. Who knows, there might be some debris in your oil that is trapped inside. It might only take a simple service, so make sure you are aware of the last A/T service you had done.
NOTE: ensure you are using the correct ATF for your specific make and model.
Basic Step #2
Most likely, when trying to locate the connector/harness for this system, you will need to find a junction connector. There might be a “master” connector, so make sure you are working with the correct one by referring to your manual. Ensure the connector itself is properly installed to ensure a good electrical connection. When the connector is located on the A/T, it may be subject to vibrations that could loosen connections or physically damage them. Not to mention, the possibility of ATF saturating the connectors and wires causing future or current problems.
Basic Step #3
It is always wise to know the overall condition of your vehicle. Since, as in this case, other systems can directly affect other systems. Uneven tires, worn suspension parts, incorrect wheels, all of this can and will cause problems in this system and perhaps others, so even things, and you might get rid of this code.
This article is strictly for informational purposes only, and technical data and service bulletins for your specific vehicle should always take priority.