P0861
Gear Shift Control Module A Communication Circuit Low
Transmission / control module communication
Generic OBD-II
Medium
What it means
P0861 means an abnormally low voltage on the communication circuit for gear shift control module 'A' — the link that carries shift and gear-position data between that module and the transmission/vehicle control system. A weak or lost signal can cause erratic shifting or push the transmission into a protective limp mode.
Medium
Can I keep driving? Engine starts and runs; the transmission may shift harshly or drop into limp mode if the module loses communication — get it diagnosed soon.
Common symptoms
What you'll notice
- Check-engine or transmission warning light on
- Harsh, erratic, or delayed shifting
- Transmission enters limp mode or holds one gear
- Wrong or missing gear-position display
Common causes
Most likely first
- Short to ground or open in the module A communication circuitLikely
- Loose or corroded connectors in the gear shift module circuitCommon
- Faulty gear shift control module ACommon
- Faulty transmission control module (TCM)Less often
How to diagnose & fix
Work through it in order
- Scan all modules for related communication (U-codes) and transmission codes, and read freeze-frame data.
- Inspect the module connectors and communication wiring for a short to ground, open, or corrosion.
- Verify power and ground to the gear shift control module.
- Repair wiring, or replace the gear shift control module / TCM as diagnosed, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0861?+
The car may still move, but expect harsh shifting or limp mode. Have it diagnosed before depending on it.
Can I just clear P0861?+
It clears, but returns as soon as the communication fault recurs. Repair the circuit or module first.
Related codes
Often seen with P0861
Read & clear P0861 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