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2018 Grand Cherokee - Battery Draining Fast & Start/Stop Not Working

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Chris P. · rep 0 · May 22, 3:27 AM · 1 replies · solved · Question

Vehicle: 2018 Jeep Grand Cherokee Limited

Hey everyone,

I've got a 2018 Jeep Grand Cherokee Limited with the 3.6L engine, and I'm having some weird electrical issues. For the past few weeks, the battery seems to be draining really fast. If I leave it parked for more than a day, it struggles to start, and sometimes needs a jump. I've had the battery tested at AutoZone, and they said it's good, but maybe a bit low on charge.

Also, the automatic start/stop feature hasn't worked in ages. It just says 'Start/Stop Unavailable' on the dash. I'm wondering if these two issues are related. Could it be a parasitic draw, or maybe something with the charging system even though the battery tested okay? No check engine light yet, but it's getting frustrating.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:27 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a classic parasitic draw or a failing charging system component, even if the battery itself tests 'good' under load. The start/stop system is very sensitive to battery health and charge levels, so its unavailability strongly points to an underlying power issue.

Here's what to investigate:

  1. Check for Parasitic Draw:

    • Method: Use a multimeter to measure current draw from the battery with the vehicle off and all doors closed (wait 15-30 minutes for modules to 'sleep'). A healthy draw should be under 50mA. If it's higher, start pulling fuses one by one to isolate the circuit causing the draw.
    • Common Culprits: Aftermarket accessories, faulty radio/infotainment module, glove box light staying on, or a stuck relay.

  2. Inspect the Charging System:

    • Alternator Output: While the engine is running, measure the voltage across the battery terminals. It should be between 13.5V and 14.7V. If it's consistently lower, the alternator might not be charging effectively.
    • Battery Sensor: Modern Jeeps have a battery sensor (often on the negative terminal) that monitors battery health and charge. A faulty sensor can give incorrect readings to the PCM, affecting charging and start/stop operation.

  3. OBD-II Scan:

    • Even without a Check Engine Light, a deeper scan with an advanced tool might reveal stored codes related to the charging system or body control module (BCM), such as P0562 (System Voltage Low) or U0401 (Invalid Data Received from ECM/PCM).

When to See a Shop: If you're uncomfortable performing electrical diagnostics or if you've identified a persistent draw but can't pinpoint the exact component, it's best to take your Grand Cherokee to a qualified mechanic. They have specialized tools to diagnose parasitic draws more efficiently and can properly test the alternator, voltage regulator, and battery sensor. Ignoring these issues can lead to premature battery failure and leave you stranded.

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