Electrical Parasitic Drain and Battery Failure
A 2019 Hyundai i30 (40,000 km) has a battery that goes flat overnight. The battery is 6 months old and tests good. The alternator charges at 14.2V. A parasitic drain test shows 350 mA draw after all modules go to sleep (spec <50 mA). You check for aftermarket accessories: a dashcam is hardwired to the fuse box. The owner says the dashcam was installed 2 months ago. You also notice the interior light stays on dimly when the door is closed. The vehicle has keyless entry and push-button start.
1. What are the likely causes of the parasitic drain, and how would you isolate the circuit?
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The dashcam hardwired to the fuse box is a prime suspect, as it may not have a proper ignition-off shutdown. The dim interior light indicates a faulty door switch or interior light circuit, causing continuous draw. To isolate: 1) Disconnect the dashcam and recheck drain; 2) If drain persists, perform a fuse pull test: measure voltage drop across fuses or remove fuses one by one while monitoring drain; 3) Check the interior light circuit: door switch, light assembly, or wiring for short to ground; 4) Use a clamp meter to trace current on individual circuits. Also check for modules not sleeping (e.g., infotainment, telematics) by monitoring current over time.
2. How would you repair the drain and ensure the battery doesn't fail again?
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For the dashcam: rewire it to a switched ignition source or install a voltage-sensing relay to cut power when battery voltage drops. For the interior light: replace faulty door switch or repair wiring. After repairs, perform a parasitic drain test to confirm draw is below 50 mA. Clear any DTCs. Advise the customer to drive the vehicle regularly or use a battery maintainer if parked for long periods. Document the repairs and the before/after drain readings. If the battery was deeply discharged, test it again and recharge if necessary.