P0861

Gear Shift Module Communication Circuit Low

Severity: High
Driving: Drive only to a garage

The communication circuit to the gear shift module is stuck low - typically shorted to earth or open circuit. Nothing can be exchanged with the module, so the transmission falls back to a failsafe and usually holds one gear.

Possible causes

CommonBus wiring shorted to earth or open circuit
CommonCorroded or water-ingressed connector at the module
CommonLow battery voltage
PossibleChafed harness shorting against the body or engine
PossibleFailed module dragging the circuit low
PossibleAftermarket wiring spliced into the bus

What you might notice

Transmission stuck in one gear
Scan tool cannot communicate with the module
Several warning lights at once
Check engine light on

What to check, in order

Check battery voltage and state of charge first.
Disconnect the gear shift module and see whether the low reading clears. If it does, the module is dragging the circuit and is the fault.
Inspect the connector for corrosion and water.
Follow the harness looking for chafe damage where it passes near hot or moving parts.
Check the fuses and earths for the module.
Ask whether aftermarket electrical work has been spliced into the bus.

Read this code from your own car

Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.

Get Pin16 on Google Play

Where this code sits

B · Body C · Chassis P · Powertrain U · Network and communication