Technical Description of OBD-II Trouble Code
Range/Performance Issue in TCM Communication Circuit
What is the meaning of P0864?
P0864 is a generic powertrain code that applies to many OBD-II vehicles (1996-newer). This includes vehicles from Dodge, Honda, Volkswagen, Ford, and others. The exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P0864 code and the malfunction indicator lamp (MIL) is illuminated, it means that the powertrain control module (PCM) has detected a problem in the transmission control module (TCM) communication circuit that is out of range or affecting performance.
While some transmission control modules are integrated into the PCM for OBD-II equipped vehicles, most are standalone components. TCM related codes may also be stored as P-codes, B-codes, or U-codes, depending on the vehicle make and model. If a P0864 code is stored, there is a high chance that there are other PCM and/or TCM codes stored as well. ABS codes may also be stored.
OBD-II equipped vehicles use a network of computers called control modules to control electronic transmission systems. These control modules communicate constantly through the controller area network (CAN).
The PCM uses input signals from various engine and transmission sensors to calculate the automatic transmission shift strategy. A high-pressure pump inside the transmission forces fluid through the valve body and into the sprag assembly, which lubricates and cools the transmission. The high-pressure fluid allows the clutches to separate from the sprag momentarily for smooth gear ratio changes. Electronic pressure control (EPC) solenoids help regulate fluid pressure.
Electronic pressure (EP) sensors provide the PCM with important data about fluid pressure at different points in the transmission.
Electronic shift solenoids interrupt the flow of high-pressure fluid to shift gears when commanded. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine efficient shifting.
Like other automatic transmission malfunctions, a transmission control system code can be caused by electrical or mechanical failures. If the PCM detects a malfunction that requires MIL illumination, it stores a P0864 code and may illuminate the MIL.
An example of a typical TCM transmission control module
What is the severity of this DTC?
If this code is stored, you may notice that your transmission shifts more harshly than usual. It is important to diagnose a P0864 code as soon as possible.
What are some of the symptoms of the code?
Symptoms of a P0864 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0864 troubleshooting steps?
To accurately diagnose a P0864 code, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and reliable vehicle information. An oscilloscope can also be helpful in diagnosing sensor outputs.
You can save time by searching for technical service bulletins (TSB) that match the stored code, vehicle information (year, make, model, and engine), and exhibited symptoms. This information can be found in your vehicle information source. If you find the right TSB, it may provide a quick solution to your diagnosis.
After connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data, write down the information in case the code is intermittent. Then, clear the codes and test drive the vehicle until one of two things happens: the code is restored or the PCM enters readiness mode.
If the PCM enters readiness mode at this point, diagnosing the code may be more difficult because it is intermittent. The condition that caused the P0864 to be stored may need to worsen before an accurate diagnosis can be made. If the code is restored, continue with the diagnosis.
You can obtain connector face views, connector pinout charts, component locator charts, wiring diagrams, and diagnostic flow charts specific to the code and vehicle by using your vehicle information source.
Perform a visual inspection of related wiring and connectors. Repair or replace any wiring that is cut, burned, or damaged.
Use the DVOM to test voltage and ground circuits at the TCM and/or PCM. If no voltage is detected, check system fuses. Replace any blown or defective fuses as necessary and retest.
If voltage and ground are detected at the TCM, test the corresponding circuit at the PCM connector. If no voltage is detected there, suspect an open circuit between the component in question and the PCM. If voltage is discovered there, suspect a defective TCM, PCM, or a programming error.
