P0864
TCM Communication Circuit Range/Performance
Transmission communication (network)
Generic OBD-II
Medium
What it means
P0864 means the data the transmission control module (TCM) exchanges with the rest of the vehicle is out of range or unreliable — a range/performance problem on the module's communication circuit. The engine still starts, but because the TCM depends on that data to shift, the transmission may shift erratically or fall back to a limp mode with limited gears. Wiring, connectors, and grounds are common causes.
Medium
Can I keep driving? The engine starts, but the transmission may shift erratically or drop into limp mode — drive gently and get it diagnosed before long trips.
Common symptoms
What you'll notice
- Check-engine light on
- Delayed, erratic, or missed shifts
- Transmission stuck in one gear or in limp mode
- Other communication or transmission codes stored alongside it
Common causes
Most likely first
- Wiring or connector fault in the TCM communication (bus) circuitLikely
- Loose or corroded connectors at the transmission control moduleCommon
- Faulty transmission control module (TCM)Common
- Fault in another module or the ECM disrupting the busLess often
- Electrical interference or a poor ground affecting the signalLess often
How to diagnose & fix
Work through it in order
- Scan all modules for communication codes to see whether the fault is TCM-specific or bus-wide.
- Inspect the TCM connectors, grounds, and communication wiring for corrosion or damage.
- Check power and ground at the TCM, and look for chafed or shorted bus wiring.
- Verify TCM software/configuration is correct for the vehicle.
- If the circuit is good, have the TCM tested and replaced/reprogrammed as needed. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0864?+
Short trips may be okay, but a communication fault can put the transmission into limp mode with limited gears. Avoid long or high-speed drives until it's fixed.
Can I just clear P0864?+
It usually returns because the communication problem is still present. Check wiring, grounds, and connectors before condemning the module.
Related codes
Often seen with P0864
Read & clear P0864 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