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2020 Wrangler JL ESS Not Working & Battery Light Flickering

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Mike T. · rep 0 · May 25, 2:23 AM · 1 replies · solved · Question

Vehicle: 2020 Jeep Wrangler Unlimited Sahara

Hey guys,

My 2020 Jeep Wrangler Unlimited Sahara has been acting up lately. The Engine Stop/Start (ESS) system completely stopped working about a week ago. I know some people disable it, but mine just says 'ESS OFF' on the dash and won't engage at all, even when all conditions are met.

On top of that, I've noticed the battery light flickering on and off very briefly while driving, usually at lower speeds or when I'm idling. It's not staying on solid, just a quick flash. I had the main battery and the auxiliary battery tested at AutoZone, and they said both were good.

Could this be an alternator issue, even if the battery light isn't staying on? Or something else entirely with the charging system? I'm worried about getting stranded.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:23 AM

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ClearTheCode admin answer:

Your 2020 Jeep Wrangler JL's symptoms (ESS not working, flickering battery light) strongly suggest an issue with the charging system, even if the batteries themselves test good. The ESS system is very sensitive to battery health and charging system performance, and it will disable itself if it detects any issues.

Here's a breakdown of potential causes:

  1. Auxiliary Battery Degradation: While AutoZone might report it as 'good,' the auxiliary battery (which powers accessories during ESS events) can degrade to a point where it can't handle the rapid discharge/recharge cycles required by ESS, even if it holds a basic charge. A specialized battery tester might reveal its true health.
  2. Alternator Issues: A flickering battery light is a classic symptom of an alternator that's starting to fail or having intermittent output. It might be generating enough voltage at times but struggling under load or at certain RPMs. This can cause voltage drops that the vehicle's computer detects, triggering the light and disabling ESS.
  3. Loose or Corroded Connections: Check the battery terminals (both main and auxiliary), the alternator connections, and the main ground strap from the battery to the chassis/engine. Loose or corroded connections can cause intermittent power delivery and charging issues.
  4. Voltage Regulator Fault: The voltage regulator, often integrated into the alternator, controls the charging output. A faulty regulator can lead to overcharging or undercharging, both of which will disable ESS and could cause the battery light to flicker.
  5. Parasitic Draw: While less likely given the flickering light, a parasitic draw could slowly drain the battery, making the ESS system unable to function properly. However, this usually results in a dead battery, not just a flickering light.

Common OBD Codes to look for (even if no CEL):

  • P0562: System Voltage Low
  • P0563: System Voltage High
  • P0620: Generator Control Circuit Malfunction

When to See a Shop:

  • If the battery light starts staying on solid.
  • If you experience any other electrical issues (dimming lights, slow cranking).
  • If you've checked connections and the issue persists. A professional can perform a comprehensive charging system test under load to pinpoint the exact fault, often using advanced diagnostic tools that can monitor real-time voltage and current output from the alternator.
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