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2021 Wrangler JL "Service Start/Stop System" Message & ESS Not Working

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Mike T. · rep 0 · May 22, 3:27 AM · 1 replies · solved · Question

Vehicle: 2021 Jeep Wrangler JL Sahara

Hi everyone,

I'm getting a persistent "Service Start/Stop System" message on my dash in my 2021 Jeep Wrangler JL Sahara. The Engine Stop/Start (ESS) feature hasn't been working at all for the past few weeks. Usually, it would turn off the engine at stoplights, but now it just stays running and the ESS light on the dash is illuminated.

I've noticed that sometimes the message appears right after starting the car, and other times it pops up while driving. I haven't had any other electrical issues, and the battery seems fine for starting the vehicle.

Has anyone else experienced this with their JL? Is this something I can troubleshoot myself, or does it sound like a dealer visit is inevitable? Any advice would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

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

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ClearTheCode admin answer:

The 'Service Start/Stop System' message and non-functional ESS in your 2021 Jeep Wrangler JL Sahara is a very common complaint. The ESS system is highly sensitive to battery health and various sensor inputs.

Here's what you can investigate:

  1. Check Battery Health: The most frequent cause is a weak or failing auxiliary battery, or even the main battery. The ESS system requires a robust electrical system to operate. Have both your main and auxiliary batteries tested for charge and cold-cranking amps (CCA) at an auto parts store. Even if the main battery starts the car fine, it might not have enough reserve capacity for ESS.
  2. Inspect Battery Terminals: Ensure both the main and auxiliary battery terminals are clean and securely tightened. Loose or corroded connections can impede proper voltage delivery.
  3. Look for OBD Codes: Although the dash message is specific, a generic OBD-II scanner might reveal codes related to battery voltage or charging system issues. Common codes could include P0562 (System Voltage Low), P0A80 (Hybrid Battery Pack Over-Temperature - less likely for ESS but related to battery management), or P0620 (Generator Control Circuit Malfunction). These codes point towards charging or battery problems.
  4. Consider Environmental Factors: ESS is designed not to engage under certain conditions, such as extreme temperatures, when the engine is cold, or if the HVAC system is working hard. While these usually don't trigger a 'Service' message, it's good to rule out.

Causes:

  • Degraded main or auxiliary battery (most common).
  • Loose or corroded battery terminals.
  • Faulty battery sensor (often integrated with the negative terminal).
  • Issues with the charging system (alternator).
  • Software glitches in the Powertrain Control Module (PCM) or Body Control Module (BCM).

When to See a Shop: If battery testing confirms both batteries are healthy, and you've checked the terminals, then it's time to visit a Jeep dealership. They have specialized diagnostic tools (like WiTech) that can read specific ESS-related fault codes and perform detailed battery system diagnostics that generic scanners cannot. They can also check for software updates for the PCM/BCM that might address known ESS issues.

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