What does P0864 mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). This may include, but is not limited to, Dodge, Honda, Volkswagen, Ford vehicles, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a P0864 code, accompanied by a malfunction indicator light (MIL), it means that the powertrain control module (PCM) has detected a problem in the range or performance of the transmission control module (TCM) communication circuit.
While some transmission control modules (for OBD-II equipped vehicles) are integrated into the PCM, most are standalone components. TCM-related codes may also be stored as P codes, B codes, or even U codes, depending on the vehicle’s make and model. If a P0864 code is stored, it is highly likely that other PCM and/or TCM codes are also stored. Anti-lock braking system (ABS) codes may also be recorded.
The electronic transmission control systems of OBD-II equipped vehicles are managed using a network of computers (called control modules). This involves constant communication between the various control modules via the controller area network (CAN).
The PCM uses input signals from multiple engine and transmission sensors to calculate the automatic shift strategy. A high-pressure pump (inside the transmission) forces fluid through the valve body and into the cam assembly; in addition to lubricating and cooling the transmission. The high-pressure fluid allows the clutches to momentarily disengage from the sprag so that the gear ratio can be smoothly changed. One or more electronic pressure control (EPC) solenoids help regulate fluid pressure.
Electronic pressure (EP) sensors provide the PCM with relevant data regarding fluid pressure at different points in the transmission.
Electronic shift solenoids are used to interrupt the flow of high-pressure fluid so that the transmission shifts when commanded. The PCM uses voltage input signals from the transmission input speed sensor and the transmission output speed sensor to determine if the transmission is shifting effectively.
As with many other automatic transmission malfunctions, a transmission control system code can be caused by an electrical or mechanical failure. If the PCM detects a malfunction that requires the MIL to illuminate, a P0864 code will be stored and the MIL may be turned on.
How severe is this DTC?
If this code is stored, you may have noticed that your transmission is shifting much harder than normal. If your vehicle has displayed a P0864 code, it should be diagnosed as soon as possible.
What are some of the symptoms of the code?
Symptoms of a P0864 fault code may include:
Irregular transmission shifting patterns
Transmission failure to shift
Reduced fuel efficiency
Transmission slipping
Delayed transmission engagement
Other transmission-related codes
ABS disabled
What are some common causes of the code?
Causes of this code may include:
Transmission sensor failure
Vehicle speed sensor failure
Open or shorted circuits in the CAN harness
Mechanical transmission failure
Defective TCM, PCM, or programming error
What are the troubleshooting steps for P0864?
You will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information to accurately diagnose a P0864 code. An oscilloscope can also be very useful for diagnosing various sensor outputs.
You can save time by searching for technical service bulletins (TSBs) that match the stored code, the vehicle (year, make, model, and engine), and the symptoms presented. This information can be found in your vehicle information source. If you find the right TSB, it might provide a quick solution to your diagnosis.
After connecting the scanner to the vehicle’s diagnostic port and retrieving all stored codes and relevant freeze frame data, note the information (in case the code proves to be intermittent). After that, clear the codes and test-drive the vehicle until one of two things happens; the code is restored or the PCM enters readiness mode.
The code may be more difficult to diagnose if the PCM enters readiness mode at this point, as the code 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, proceed with the diagnosis.
You can obtain connector face views, connector pinout charts, component location diagrams, wiring diagrams, and diagnostic flowcharts (related to the code and the vehicle in question) using your vehicle information source.
Perform a visual inspection of the associated wiring and connectors. Repair or replace any wiring that is cut, burned, or damaged.
Use the DVOM to test the voltage and ground circuits at the TCM and/or PCM. If no voltage is detected, check the system fuses. Replace any blown or faulty fuses as needed 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 found there, suspect a faulty TCM, PCM, or a programming error.
Most communication error codes can be attributed to a programming issue
