Generator will not crank, controller shows E-04

Safety: Disable automatic start. Wear eye protection when working around batteries.

• Measure battery voltage: With a multimeter, measure across the battery posts. A healthy 12 V battery should read about 12.6 V at rest. Below ~11.8 V indicates deep discharge.
• Inspect terminals: Check for corrosion (white/green buildup) on battery posts and cable clamps. Clean with a baking soda and water solution, rinse, dry, and tighten clamps securely.
• Check battery charger: Locate the CAT battery charger module in the control panel. Confirm AC supply to the charger is present and its DC output is around 13.2–13.6 V. Replace the charger if it has input power but no DC output.
• Recharge or replace battery: Use an external smart charger to fully charge the battery. If it will not hold charge or is older than 4–5 years, replace with a CAT-specified starting battery of the correct CCA rating.
• Clear code and test: After restoring proper voltage, clear E-04 on the controller and perform a manual start test.

Persistent low voltage after charger replacement may indicate wiring issues or a parasitic load that should be diagnosed by a technician.