What it means
A receiving module detected implausible data from generator (alternator) control module A. Field excitation, output current or voltage values fail plausibility checks and are rejected.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Generator A control module manages or reports alternator operation, including electrical output information shared with other vehicle modules. U042E is set when a receiving module rejects those reports as implausible; a module or input fault, software mismatch, or gateway routing problem can be responsible.
Common causes
Most likely first.
- Module internal fault or sensor input drift
- Software version mismatch after replacement
- Gateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and review freeze-frame data for U042E alongside charging-system, battery, and network codes.
- Check the battery and charging-system warning indicators and note any dimming lights, slow cranking, or other signs of unstable electrical supply.
- Inspect generator A, its control-module connections, the gateway, and visible CAN wiring for looseness, corrosion, heat damage, or belt-related problems.
- Use a scan tool to compare reported generator output or control values with an independent charging-system check, following the manufacturer's specification.
- Check module software compatibility and CAN routing, then test generator A control inputs and communication before replacing the module.
Common fixes
- Clean and secure a loose or corroded generator control or ground connection.
- Repair damaged wiring or a belt fault affecting generator operation.
- Repair a confirmed charging-system or generator fault.
- Correct a gateway routing or software mismatch, or replace the generator A control module if testing confirms it has failed.
Can I keep driving?
Avoid unnecessary driving if the charging warning is on, electrical systems are failing, or the engine may stall; a charging fault can drain the battery and leave the vehicle unable to restart. If the vehicle is in limp mode or lights are dimming, stop safely and arrange assistance.
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.