Error Code P085B is defined as Gear Shift Control Module “B” Communication Circuit Low. Error Code P085B is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

The PCM (powertrain control module, also known as ECM or engine control module) monitors the gear shift control module. It sets the error code if it sees a problem communicating with the gear shift control module, particularly if the data sent to the PCM is lower than the expected or the specifications set by the manufacturer.

Common Symptoms

Check Engine light or Service Engine Soon Warning light on.

Possible Causes

  • Defective Gear Shift Control Module “B”
  • Open or shorted Gear Shift Control Module “B”
  • Poor electrical connection in the Gear Shift Control Module “B”

How to Check

Check for the possible causes listed above; inspect all related wirings, connectors, and harness.

Then, check for damaged components such as bent, broken, pushed out, and corroded connector pins.

How to Fix

  • Replacement of faulty Gear Shift Control Module “B”
  • Repair or replacement of open or short wiring in the Gear Shift Control Module “B”
  • Repair or replacement of broken, burnt, or chafed wires, or corroded connector pins

Make sure you test drive the vehicle after completing any repairs to see if the condition is fixed.

Don’t forget to erase all P code(s) first before taking the vehicle for a test drive. This will turn the Check Engine light off, which will give you a good idea if your repairs worked as the Check Engine light will be activated if the problem remains.

This is a serious and complicated problem, which means it must be addressed by an expert technician as soon as possible.