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2020 RX 350 Battery Draining Overnight - Parasitic Draw?

0

Mike T. · rep 0 · May 22, 4:43 AM · 1 replies · solved · Question

Vehicle: 2020 Lexus RX 350 F Sport

My 2020 Lexus RX 350 F Sport has been having a really annoying problem lately. For the past few weeks, if I leave it parked for more than 12-18 hours, the battery is completely dead. I've had to jump-start it multiple times. I've checked all the lights, and nothing seems to be left on.

I had the battery tested, and it's supposedly good, and the alternator is charging fine. It feels like something is draining the battery while the car is off. Could this be a parasitic draw? What should I be looking for?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:43 AM

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ClearTheCode admin answer:

A parasitic draw is a very likely cause when your battery dies overnight despite being healthy and the charging system working. This means a component is drawing power even when the vehicle is off. Here's how to approach it:

  1. Verify Battery and Charging System: While you've had it tested, ensure the battery is fully charged and load-tested. A weak battery can fail quickly. Also, confirm the alternator output is within specifications (typically 13.5-14.5 volts).
  2. Check for Obvious Culprits:
    • Glove Box/Trunk Lights: Ensure they turn off when closed.
    • Aftermarket Accessories: Any dash cams, remote starters, or audio systems not professionally installed can be a source.
    • Door Ajar Switches: A faulty switch might keep a module awake, thinking a door is open.
  3. Perform a Parasitic Draw Test (Advanced):
    • Tools Needed: A multimeter capable of reading amps (at least 10A range).
    • Procedure: Disconnect the negative battery terminal. Connect the multimeter in series between the negative battery post and the negative battery cable. Ensure all doors are closed, and the car is 'asleep' (wait 15-30 minutes after connecting to allow modules to power down). A normal draw is typically 20-50 milliamps (0.02-0.05 amps). Anything significantly higher indicates a problem.
    • Isolate the Circuit: If the draw is high, start pulling fuses one by one while monitoring the multimeter. When the draw drops significantly, you've found the problematic circuit. Then, you can investigate components on that circuit.

Common Causes of Parasitic Draw in Lexus Vehicles:

  • Faulty Audio/Navigation Unit: Can sometimes stay partially awake.
  • Stuck Relays: A relay that doesn't fully open can keep a circuit powered.
  • Faulty Body Control Module (BCM) or Gateway ECU: These central modules can sometimes malfunction and prevent the car from entering sleep mode.
  • Power Seat Modules: Sometimes, these can develop internal shorts or stay active.
  • Keyless Entry/Smart Key System: Issues with the antenna or module can cause constant power draw.

When to See a Shop: If you're uncomfortable performing a parasitic draw test yourself, or if you've identified a circuit but can't pinpoint the exact component, it's best to take your RX 350 to a Lexus dealership or an experienced automotive electrician. They have specialized diagnostic tools to quickly identify the source of the draw and repair it, potentially saving you from replacing multiple components unnecessarily.

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