Fault code P0864 is called “TCM Communication Circuit Range/Performance” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0864
If your OBD-II equipped vehicle has stored code P0864, it means that the PCM has detected an operating range mismatch in the TCM module communication circuit. The error is accompanied by an illuminated lamp on the instrument panel.
In most cases, the TCM module is integrated in a single housing with the PCM. However, the part of the module that controls the automatic transmission function may be powered separately.
The TCM normally receives power only when the ignition switch is on, starting, or in the operating position. This circuit is equipped with a fuse, fusible link, or relay. Often the PCM and TCM receive power from the same relay, although on separate circuits.
The electronic transmission control systems in OBD-II equipped vehicles are controlled by a network of computers called control modules. This involves constant communication between the various control modules via the Controller Area Network (CAN).
Each time the engine is started, the PCM performs a self-test of all controllers. If no normal signal is detected in the communication circuit. Code P0864 will be stored and the malfunction indicator light may illuminate.
On some models, the transmission controller may put the operation into an emergency mode. This means that only 2-3 gears will be available for travel.
Symptoms of vehicle malfunctions
The main signal that an error P0864 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- Other related fault codes may also be present.
- Sharp or unstable gear shifting.
- Delayed gear engagement.
- Emergency mode of transmission operation.
- Intermittent readings or complete speedometer malfunction.
- Electronic traction control system may malfunction.
- Anti-lock braking system (ABS) malfunction.
Diagnostic fault code P0864 is considered serious because the transmission may operate in emergency mode, making the vehicle barely drivable. For this reason, this error should be corrected as soon as possible.
Factors that can cause this error code
The error code P0864 can mean that one or more of the following problems have occurred:
- Defective power relay PCM or TCM.
- Fuse blown.
- Open or short circuit in CAN circuit.
- Damaged, corroded wiring or connectors.
- Faulty vehicle speed sensor.
- Mechanical failure of transmission.
- Defective TCM, PCM module or programming error.
How to fix or reset OBD-2 code P0864
Some suggested steps for troubleshooting and fix the error code P0864:
- Inspect the wiring for damage, abrasions, breaks, and shorts. If wiring is damaged, repair or replace it.
- Remove all diagnostic trouble codes from the PCM and perform a test drive to see if diagnostic trouble code P0864 returns.
- If the code returns, check the TCM, PCM relay to make sure it is working properly.
- Inspect and check the fuse and fusible link.
- Check the wiring diagram of the relay and fuse system.
- Clear the fault codes again and perform a test drive.
- Insert the key into the ignition switch and turn it to the on position. If the Check Engine light does not come on, but the code in memory appears again, the relay may be faulty.
- If the relay is faulty, it may be necessary to replace and reprogram TCM, PCM.
Diagnose and repair of problems
To rule out all variants of error P0864, visually inspect the wiring, check the voltage on the battery. Also check the battery terminals and cables for loose connections.
Ensure that the system voltage is as specified in the manual. The charging system is fully functional, and the battery is in good condition, begin the diagnostic procedure.
Locate the starting point of the TCM power circuit. This is usually the ignition switch, so use a digital multimeter to check the voltage at this wire or terminal. Compare the reading with the value given in the manual, and repair if necessary if an abnormality is found.
If the code remains, but the power supply to and from the ignition switch is within the specified range. Note and test the power supply to the fuse box and then to the TCM connector. If abnormalities are found, make the necessary repairs. To ensure that all electrical parameters are in accordance with the manufacturer’s specifications.
The steps described above will help resolve error P0864, but in some cases where the cause is not obvious, intermittent faults may be present. Also, if the TCM is already damaged it may require repair by a specialized repair shop.
On which vehicles does this problem occur most frequently
Fault code P0864 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Audi (Q7)
- Dodge
- Ford
- Honda (Accord)
- Porsche (Cayenne)
- Skoda (Octavia)
- Volkswagen (Beetle, Jetta, Passat, Polo, Tiguan, Touareg)
Fault code P0864 can sometimes be found with other errors. The most common are the following: P0863, P0865, P0866.
