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2019 Wrangler JL ESS Not Working - Battery or Something Else?

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Kim L. · rep 0 · May 22, 3:21 AM · 1 replies · solved · Question

Vehicle: 2019 Jeep Wrangler Sahara

Hey everyone, I've got a 2019 Jeep Wrangler Sahara with the 3.6L Pentastar, and lately, the Engine Stop-Start (ESS) system just isn't engaging. It used to work perfectly, but now it almost never activates, even on long drives.

I've checked the main battery, and it seems fine, no issues starting the vehicle. I know there's an auxiliary battery for the ESS, but I'm not sure how to test it or if that's even the problem. The 'ESS OFF' light isn't on, it just doesn't stop the engine.

Could this be a sensor issue, or is it almost certainly a battery problem? Any advice on what to check first before I take it to the dealer would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:21 AM

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ClearTheCode admin answer:

The Engine Stop-Start (ESS) system in your 2019 Jeep Wrangler Sahara relies on several conditions to be met before it will activate. When it stops working, it's often related to battery health or specific operational parameters.

Common Causes:

  1. Auxiliary Battery Failure: The most frequent cause. The ESS system uses a dedicated auxiliary battery (usually smaller, located near the main battery) to power accessories when the engine is off. If this battery is weak or dead, the ESS system will not engage.
  2. Main Battery Health: While your main battery might start the car, if its overall charge or health is below a certain threshold, the ESS system will disable itself to ensure reliable starting.
  3. Environmental Conditions: Extreme temperatures (very hot or very cold) can prevent ESS from activating.
  4. HVAC Demand: If the climate control system is working hard to reach a set temperature, the ESS may remain off.
  5. Hood Latch Sensor: A faulty hood latch sensor can trick the system into thinking the hood is open, disabling ESS for safety.
  6. Brake Pedal Pressure: Insufficient brake pedal pressure at a stop can prevent activation.
  7. Recent Battery Disconnect/Reset: The system may need a drive cycle to recalibrate after a battery service.

Troubleshooting Steps:

  1. Check Auxiliary Battery: This is usually the first suspect. Many auto parts stores can test both your main and auxiliary batteries. A weak auxiliary battery often won't throw a specific OBD code, but a general system voltage code like P0562 (System Voltage Low) could indicate an issue.
  2. Verify Main Battery Health: Ensure your main battery is fully charged and in good condition.
  3. Inspect Hood Latch Sensor: Make sure the hood is fully closed and the sensor is functioning correctly.
  4. Monitor Driving Conditions: Pay attention to outside temperature and HVAC settings.
  5. Check for OBD Codes: Even without a 'Check Engine' light, a scan tool might reveal pending or stored codes related to battery or system voltage.

When to See a Shop:

If testing the batteries doesn't resolve the issue, or if you're uncomfortable performing these checks, it's best to visit a certified Jeep service center. They have specialized diagnostic tools to pinpoint sensor failures or more complex electrical issues that might be preventing the ESS from functioning.

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