Error Code P0861 is defined as Gear Shift Module Communication Circuit – Low Input. This is a generic trouble code, meaning it applies to vehicles equipped with the OBD-II system, particularly those made from 1996 up to the present. The problem is related to the transmission, including pressure errors and sensor issues.

This code usually appears when there’s a fault with the gear shift module communication circuit is detected by the PCM (powertrain control module, also known as ECM or engine control module).

Common Symptoms

As with other codes, this error code activates the Check Engine light. Other symptoms include:

  • Rough or difficulty shifting in or out of gear
  • Vehicle may not shift in or out of gear
  • Lack of traction in slippery conditions
  • Traction control light turned on or blinking
  • Increased fuel consumption
  • Vehicle may enter “limp” mode

Possible Causes

  • Damaged, open, or shorted to ground wires or connectors
  • Excessively level of moisture accumulated in the gear shift module sensor connector
  • A damaged manual lever position sensor

How to Check

First off, check for the stored codes using the OBD-II scanner.

Then, inspect all the connectors and wirings related to the gear shift module. Look for signs of corrosion or damage, such as burnt wire, etc.

If possible, use a specialized tool such as Autohex to pinpoint the error or the malfunction.

It is best to use a memory saving device to store the memory of other modules during reprogramming.

To see the pin values and identify which control modules are in operation, use a diagnostic CAN scanner.

Test the control module ground circuits for continuity with battery ground.

Look for any loose, damaged or corroded connectors that could increase the resistance in the circuit.

How to Fix

  • Repair or replacement of damaged connectors, wires, and related components
  • Repair or replacement of defective gear shift lever
  • Repair or replacement of defective gear shift module

This error code is a serious safety problem, so it must be addressed as soon as possible.

Many times, the gear shift module is incorrectly determined to be the cause of the problem, when the actual cause is as simple as electrical wiring, switch, or sensor issue. It’s best to conduct a thorough diagnosis.