The OBD2 code P0864 indicates a problem within the Transmission Control Module (TCM) communication circuit, specifically pointing to issues with range or performance. This code suggests that the vehicle’s onboard computer is having trouble talking to the transmission’s control module, which can lead to a variety of driveability problems, including intermittent stalling, going into limp mode, or even preventing the engine from starting.
P0864 quick overview
| Meaning | P0864: TCM Communication Circuit Range/Performance |
| Is it serious? | Yes, it can significantly impact the vehicle’s performance and may lead to transmission or engine issues. |
| Possible causes | – Faulty TCM – Corroded, damaged, or loose wiring/connector in the TCM circuit – Faulty power supply to the TCM – Issues within the vehicle’s CAN (Controller Area Network) bus system |
| How to diagnose? | Inspect the TCM for any signs of damage or water intrusion Check TCM-related wiring and connectors for corrosion, damage, or loose connections Test TCM power and ground circuits to ensure they’re receiving proper voltage and have good continuity Evaluate the vehicle’s electrical system thoroughly, focusing on circuits that could affect TCM communication |
P0864 Meaning
For those unfamiliar with the intricacies of vehicle electronics, the Transmission Control Module (TCM) acts like a mini-computer that manages how the car shifts gears. When a P0864 code pops up, it’s like saying this mini-computer is having trouble receiving or sending messages correctly, which could make your car act erratically or even refuse to move properly.
This issue could be as simple as a loose wire or as complex as needing a new TCM. Getting to the bottom of this is crucial because smooth communication between the car’s components is key to a well-functioning vehicle, much like ensuring good Wi-Fi for your devices at home.
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How to fix P0864 – learn from mechanics
I looked into P0864 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Volkswagen
Vehicle Information 2008 Volkswagen Jetta SEL 2.5L
Issue + Repair History
- Crank no start condition.
- No fuel pressure or power to the fuel pump.
- Tested fuses and relays, all appear functional.
- No immobilizer light illuminated.
- Spark present; engine fires with fuel introduction in the intake.
- Diagnostic code: Pending P0864 TCM communication circuit range performance.
Other OBD2 Codes + Test Results
- Pending P0864: TCM communication circuit range performance.
Mechanic Suggestions
- Try applying direct voltage to the fuel pump motor.
- Consider that the fuel pump may not run until the TCM comes online properly.
- If there is no power supply to the pump, backtrack from there to diagnose the issue. Verify fuses, relays, and check for a shorted power supply. Test fuel pump by hotwiring to check pressure and injector pulse.
- Utilize a wiring diagram to trace the circuit back from the pump. Some German cars have a complex relay system; investigate all relays in the system, as the culprit may not be directly related to the fuel pump.
- Diagnose the P0864 code first, as all modules related to vehicle operation need communication before the vehicle can run.
Final Fix
- Dealership repair revealed a broken power feed wire to the ECM, intermittently making a connection. Wire was repaired, resolving the intermittent no-start issue.
Case #2: Toyota
Vehicle Information 2015 Toyota Camry LE 2.5L
Issue + Repair History
- Vehicle exhibits intermittent stalling.
- Check engine light illuminated.
- Scanned codes, found P0864: TCM communication circuit range performance.
- No prior repair history related to this issue.
Other OBD2 Codes + Test Results
- Only code present: P0864: TCM communication circuit range performance.
Mechanic Suggestions
- Verify the condition of the transmission control module (TCM). Inspect for physical damage or signs of water intrusion.
- Check all TCM-related wiring and connectors for corrosion, damage, or loose connections.
- Test the TCM power and ground circuits to ensure proper voltage and continuity.
- Perform a thorough inspection of the vehicle’s electrical system, paying attention to any components or circuits that could affect TCM communication.
Final Fix
- After inspecting the TCM and associated wiring, a corroded connector pin was discovered. Cleaning the connector and securing the pin resolved the intermittent communication issue, and the vehicle no longer experienced stalling.
Case #3: Honda
Vehicle Information 2017 Honda Accord EX-L 3.5L
Issue + Repair History
- Vehicle intermittently goes into limp mode.
- Check engine light comes on sporadically.
- Scanned codes, found P0864: TCM communication circuit range performance.
- No previous repairs related to this issue.
Other OBD2 Codes + Test Results
- Sole code present: P0864: TCM communication circuit range performance.
Mechanic Suggestions
- Inspect the transmission control module (TCM) for any signs of physical damage or water intrusion.
- Check all TCM-related wiring and connectors for corrosion, damage, or loose connections.
- Test the TCM power and ground circuits for proper voltage and continuity.
- Conduct a comprehensive evaluation of the vehicle’s electrical system, focusing on components or circuits that could impact TCM communication.
Final Fix
- Upon inspection, a damaged TCM connector was identified. Replacing the connector and ensuring proper connection resolved the intermittent limp mode and check engine light issues, restoring normal vehicle operation.
How to diagnose P0864
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Inspect the TCM | Look for physical damage or signs of water intrusion. |
| Check TCM-related wiring and connectors | Examine for corrosion, damage, or loose connections. |
| Test TCM power and ground circuits | Verify proper voltage and continuity. |
| Evaluate the vehicle’s electrical system | Focus on the overall system, especially components affecting TCM communication. |
Addressing a P0864 code involves careful inspection and testing of the TCM and its related circuits to ensure all connections are secure and all components are functioning correctly. Given the complexity of modern vehicle electrical systems, professional diagnostics and repairs are often required to accurately identify and correct the underlying problem, ensuring the vehicle operates smoothly and reliably.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko