What it means
The gear shift control module B communication circuit reports a communication circuit low condition. Shift command exchange is impaired.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Gear shift control module B communicates shift commands and status over a vehicle data bus. This code sets when the communication circuit is detected below its expected electrical level, which can point to a bus wire shorted to ground or a low module output.
Common causes
Most likely first.
- Bus wire shorted to ground
- Module output low
- Gateway module routing CAN messages incorrectly
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and scan all modules for network codes to determine whether the low condition affects module B alone or the shared bus.
- Check communication with module B and note whether other modules report it as unavailable.
- Inspect the module B bus wiring and connectors for a short to ground, damaged insulation, corrosion, or loose pins.
- Test the communication circuit for a ground short and check module B power and ground using the manufacturer's procedures.
- If the physical bus checks pass, verify gateway routing and module output before replacing any module.
Common fixes
- Repair a bus wire shorted to ground.
- Clean and secure the module B network connector.
- Restore faulty power or ground to module B.
- Correct a confirmed gateway routing fault.
- Repair or replace module B only if circuit tests confirm its output is low.
Can I keep driving?
A low communication circuit can interrupt shift commands and may leave the transmission in a protective gear. Limit driving and stop if gear selection or shifting becomes unreliable.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.