What it means
The gear shift control module A 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 A communicates shift-related data over a vehicle network. This code sets when the Module A communication circuit is detected at a low electrical level, which can interrupt or corrupt those messages.
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
- Save freeze-frame data and scan all modules for communication codes to determine whether the low condition affects only Module A or other network devices too.
- Check Module A's scan-tool connection and network status for lost or intermittent messages.
- Inspect the Module A network connector and wiring for a conductor shorted to ground, damaged insulation, corrosion, or bent pins.
- With the vehicle's circuit safely isolated as specified by the manufacturer, test the network line for a short to ground.
- If no wiring short is found, check Module A output and gateway routing using the manufacturer's network diagnostic procedure.
Common fixes
- Repair a network wire shorted to ground.
- Clean, secure, or repair Module A's connector and wiring.
- Correct gateway routing or configuration if it is disrupting Module A communication.
- Repair or replace Module A if testing confirms its output is holding the circuit low.
Can I keep driving?
If shifting is harsh, delayed, or the vehicle is in limp mode, avoid continued driving except to reach a safe place; the low communication condition can interrupt shift commands. Stop if drive is lost or the transmission behaves unpredictably.
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.