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ESS (Engine Stop-Start) system not working on my 2020 Wrangler JL

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

Vehicle: 2020 Jeep Wrangler JL Rubicon

Hi all, I've got a 2020 Jeep Wrangler JL Rubicon, and my Engine Stop-Start (ESS) system has completely stopped working. The ESS OFF light is always on, and it never engages, even under ideal conditions (engine warm, battery charged, AC not blasting, etc.).

I've had the battery tested, and it seems fine, but I'm wondering if there's a specific sensor or something else electrical that might be causing this. There are no other warning lights on the dash, just the ESS OFF indicator.

Is this a common issue with the JLs? What should I be looking at? Any diagnostic steps I can try before taking it to the dealer?

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

The Engine Stop-Start (ESS) system in your 2020 Jeep Wrangler JL is a complex system that relies on numerous inputs to function correctly. When it stops working, it's often due to one of several common electrical or sensor-related issues.

  1. Auxiliary Battery Failure:

    • Cause: Jeep ESS systems use two batteries: a main starting battery and a smaller auxiliary battery. The auxiliary battery powers accessories when the engine is stopped. If this battery fails or degrades, the ESS system will disable itself.
    • Action: Even if your main battery tests fine, the auxiliary battery (often located under the main battery tray) needs to be tested. A failing auxiliary battery is a very common reason for ESS malfunction.

  2. Battery Sensor Issues:

    • Cause: The battery sensor (often on the negative battery terminal) monitors the battery's state of charge, temperature, and health. A faulty sensor can provide incorrect readings, leading the ESS system to disable itself to protect the battery.
    • Action: Check for loose connections at the battery sensor. If you have an OBD-II scanner, look for codes like B1640 (Battery Sensor Circuit Malfunction) or similar codes related to battery monitoring.

  3. Hood Latch Sensor:

    • Cause: The ESS system requires the hood to be fully closed. A faulty hood latch sensor can trick the system into thinking the hood is open, preventing ESS engagement.
    • Action: Visually inspect the hood latch and its wiring. If you have a scanner, check for codes like B181C (Hood Ajar Switch Circuit Malfunction).

  4. Brake Pedal Position Sensor:

    • Cause: The ESS system relies on accurate brake pedal input. A faulty brake pedal position sensor can cause the system to malfunction.
    • Action: Look for any related brake system warning lights. Codes like C0040 (Brake Pedal Position Sensor A Circuit) might appear.

  5. Software/Module Glitch:

    • Cause: Sometimes the Body Control Module (BCM) or Powertrain Control Module (PCM) can experience a temporary glitch.
    • Action: A battery disconnect (as mentioned in the Uconnect answer) can sometimes reset modules. However, a dealership might need to perform a software update or module reflash.

When to See a Shop:

  • If replacing the auxiliary battery doesn't resolve the issue.
  • If you're getting specific OBD-II codes related to the ESS system, battery, or sensors that you can't diagnose yourself.
  • If the issue persists and you've checked the obvious culprits. A professional can use advanced diagnostic tools to pinpoint the exact sensor or module causing the problem.
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