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2017 A4 Battery Drain Overnight - Parasitic Draw Mystery

0

Mike T. · rep 0 · May 25, 3:14 AM · 1 replies · solved · Question

Vehicle: 2017 Audi A4 2.0T Quattro

My 2017 Audi A4 2.0T Quattro has developed a really annoying battery drain problem. For the past few weeks, if I leave it parked overnight, the battery is completely dead by morning. I've already replaced the battery with a brand new OEM one, thinking that was the issue, but the problem persists.

I've checked for obvious culprits like lights left on, but everything seems normal. No aftermarket accessories are installed that could be drawing power. It's driving me crazy having to jump-start it every day. Could this be a module staying awake, or something else more sinister?

Has anyone tackled a parasitic draw on their A4? What should I be looking for? I'm trying to avoid a huge diagnostic bill at the dealer if it's something I can track down myself.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:14 AM

0

ClearTheCode admin answer:

Persistent battery drain, even with a new battery, almost always points to a parasitic draw. This means something in your 2017 Audi A4 is continuously drawing power when the car is off and locked. Tracking it down can be tedious but is often solvable.

  1. Perform a Parasitic Draw Test:
    • Ensure the car has been off and locked for at least 30-60 minutes to allow all modules to 'go to sleep'.
    • Disconnect the negative battery terminal.
    • Connect a multimeter in series between the negative battery post and the disconnected negative battery cable (set to measure amperage, typically 10A or 20A range).
    • A normal draw should be around 20-50 milliamps (0.02-0.05 amps). Anything significantly higher indicates a problem.
  2. Pull Fuses Systematically:
    • With the multimeter connected and showing a high draw, begin pulling fuses one by one from the fuse boxes (check both interior and engine bay).
    • Watch the multimeter reading. When the amperage drops significantly, you've found the circuit responsible for the draw.
  3. Identify the Culprit Module/Component:
    • Once you've isolated the circuit, identify what components or modules are on that circuit. Common culprits include:
      • Infotainment system (MMI) not shutting down properly.
      • Comfort Control Module (CCM) or Body Control Module (BCM) faults.
      • Faulty alternator diode (causing a slow drain).
      • Glove box light, trunk light, or vanity mirror lights staying on.
      • Aftermarket alarms or tracking devices (though you mentioned none).

Common Causes:

  • Stuck Relay: A relay that doesn't de-energize can keep a circuit active.
  • Faulty Module: A control module (e.g., MMI, BCM, gateway) that fails to enter sleep mode.
  • Wiring Short: A short to ground can cause a constant draw, though this often blows fuses.

When to See a Shop: If you're uncomfortable performing the parasitic draw test yourself, or if you identify a problematic circuit but can't pinpoint the exact component, it's best to consult an Audi specialist. They have advanced diagnostic equipment that can communicate with individual modules to determine which one is awake or faulty. While there isn't a specific OBD-II code for parasitic draw, a shop can check for codes like U0100 (Lost Communication with ECM/PCM) or U0140 (Lost Communication with Body Control Module) which might indicate a module failing to shut down, or specific B-codes relating to electrical faults within modules.

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