Bosch EV charger shows E109 and stops charging; may occur intermittently during a session.

Safety first: A missing or poor ground is dangerous. Turn OFF the breaker and do not use the charger until the ground is verified.

• Visual inspection: Check that the metal conduit or ground wire to the charger is intact and not damaged. Look for signs of corrosion at external junction boxes.
• Electrician ground test: Have a licensed electrician open the charger’s wiring compartment and verify that the ground conductor is securely landed on the ground terminal and that continuity to the main panel ground bar is solid.
• Correct wiring errors: Ensure no bootleg grounds or shared neutrals are used. The Bosch charger requires a dedicated equipment ground.
• Internal fault: If the external ground is confirmed good but E109 persists, the internal ground monitoring circuit or PCB may be defective and require replacement.