Engine cranks but will not start; ECU 1.2 displayed; sometimes starts then stalls immediately.

Safety: Disable auto-start and isolate the battery before handling relays or wiring.

• Locate ECU main relay: In the generator control cabinet or engine-mounted relay box, identify the ECU/ignition main relay (refer to the Volvo Penta wiring diagram for your model).
• Inspect and reseat: Pull the relay straight out, inspect pins for discoloration or burning, then reseat firmly. Clean the socket with electrical contact cleaner if dirty.
• Swap test: If there is an identical relay nearby (e.g., fuel pump relay), temporarily swap them to see if the fault follows the relay. Replace any suspect relay with a genuine Volvo Penta-rated relay.
• Check voltage during crank: Monitor battery voltage while cranking. If it drops below about 9.5 V (12 V system) or 19 V (24 V system), the ECU may drop out. Service or replace weak batteries and check starter current draw.
• Inspect harness: Follow the harness from the relay to the ECU. Look for chafing, crushed sections, or oil-soaked connectors. Repair any damaged wiring with proper crimp or solder joints and heat-shrink.