P0865
TCM Communication Circuit Low
Transmission controls
Generic OBD-II
Medium
What it means
P0865 sets when the low-voltage side of the transmission control module's communication circuit is faulty — here TCM means the Transmission Control Module, not traction control. Losing this link can cause erratic shifting or limp mode. Wiring, connectors, and power/ground faults are more common than a failed module. The engine still starts and runs.
Medium
Can I keep driving? Usually — but expect limp mode or shifting problems from lost transmission-controller communication; get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Delayed, erratic, or no shifting
- Transmission may enter limp mode (fixed gear)
- Loss of communication between the TCM and other modules
Common causes
Most likely first
- Wiring or connector fault on the TCM communication circuit (short to ground / low signal)Likely
- Loose or corroded connectors at the TCMCommon
- Poor power or ground to the TCMCommon
- Faulty transmission control module (TCM)Less often
- Faulty PCM or other module on the network — least likelyLess often
How to diagnose & fix
Work through it in order
- Scan all modules for related communication codes.
- Inspect the TCM connector and communication wiring for shorts to ground or corrosion.
- Verify the TCM's power and ground circuits.
- Test the communication (bus) circuit against wiring specs.
- Replace or reflash the TCM if confirmed faulty. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0865?+
The engine still runs, but the transmission may shift erratically or drop into limp mode when communication is lost. Have it checked soon.
Can I just clear P0865?+
It returns until the communication wiring, connectors, or module fault is repaired.
Related codes
Often seen with P0865
Read & clear P0865 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX