When your 2021 Honda Accord's lights illuminate normally but the engine refuses to turn over, you're dealing with a starting circuit issue rather than a completely dead battery. This symptom points to specific components in the starting system that need investigation.
Why Lights Work But Engine Won't Crank
Dashboard and headlights require only a few amps to operate, while the starter motor demands 100-200 amps. A battery can have enough reserve to power lights while being too weak to crank the engine. However, if lights stay bright and don't dim at all when you press the start button, the starter motor isn't even attempting to engage.
Push Button Start System Specifics
The 2021 Accord's push button start system requires the key fob to be recognized before allowing starting. If the fob battery is weak, the system may not detect it. Try holding the fob directly against the start button - there's a backup reader that can detect a fob with a depleted battery.
Brake Pedal Switch Requirements
Honda's start system requires the brake pedal to be fully depressed before the starter engages. A faulty brake pedal position switch can prevent starting even when you think you're pressing hard enough. Try pumping the brake firmly several times then holding it down while pressing start.
Shift Interlock and Park Position
The transmission range sensor must confirm the vehicle is in Park before allowing starting. Occasionally this sensor can malfunction or the shifter may not fully engage Park. Try shifting to Neutral and attempting to start - if it works in Neutral but not Park, the range sensor needs attention.
Starter Motor and Relay Issues
If the battery is verified good and all interlocks are satisfied, the starter motor or its control circuit may have failed. The 2021 Accord uses a starter relay in the under-hood fuse box - listen for a click from this relay when pressing start. No click means the PCM isn't commanding the relay or the relay has failed.
Immobilizer System Considerations
Honda's immobilizer system can prevent starting if it doesn't recognize the key. The green key light on the dashboard should flash briefly then turn off. If it stays on or blinks continuously, there's an immobilizer communication issue that may require dealer-level diagnostic equipment.