What it means
The gear shift control module A reports a supply voltage above the operating range.
At a glance
- Usually lights the check-engine light
How it works
The gear shift control module A operates and monitors part of the transmission’s shift control system. This code sets when its reported supply voltage rises above the module’s operating range, which can happen if the alternator regulator overcharges or a brief voltage surge occurs after a heavy electrical load is disconnected.
Common causes
Most likely first.
- Alternator regulator failed to limit output
- Load dump transient after disconnecting a heavy load
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
- Check freeze-frame data and module voltage readings to see whether the fault occurred during charging or after a sudden load change.
- Inspect the battery terminals, grounds, and charging-system connections for looseness, corrosion, or signs of overheating.
- Measure charging voltage at the battery under the conditions specified by the manufacturer to check whether the alternator regulator is allowing excessive output.
- Check for recent battery, alternator, or high-current accessory disconnections that could have produced a voltage transient.
- If charging voltage is within specification, have the supply and ground circuits to gear shift control module A checked for voltage spikes before condemning the module.
Common fixes
- Clean and secure loose or corroded battery and charging-system connections.
- Repair a poor engine or transmission ground affecting module A’s supply.
- Replace a faulty alternator regulator or alternator if charging output exceeds the manufacturer’s specification.
- Repair damaged supply wiring or a connection that allows voltage spikes to reach module A.
Can I keep driving?
If shifts are harsh, delayed, slipping, or the transmission enters limp mode, avoid towing, hard acceleration, and long trips; stop somewhere safe if the transmission loses drive. Excess supply voltage can disrupt shifting and may damage transmission electronics, so arrange diagnosis promptly.
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.