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ESS System Malfunction in 2021 Pacifica - Won't Activate or Stalls

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Mike T. · rep 0 · May 25, 4:26 AM · 1 replies · solved · Question

Vehicle: 2021 Chrysler Pacifica Pinnacle

Hi everyone,

I'm having some trouble with the Engine Start/Stop (ESS) system in my 2021 Chrysler Pacifica Pinnacle. Lately, it's been very inconsistent. Sometimes it won't activate at all when I come to a stop, even when all conditions seem right. Other times, it engages, shuts the engine off, but then struggles to restart, or even stalls completely, which is quite alarming.

I've checked the main battery, and it seems fine, but I know the ESS system uses an auxiliary battery. Could that be the culprit? Is this a common software glitch in the newer Pacificas, or should I be looking at something more serious? Any insights would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:26 AM

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ClearTheCode admin answer:

The Engine Start/Stop (ESS) system in your 2021 Chrysler Pacifica is designed to save fuel by shutting off the engine when the vehicle comes to a stop and restarting it when you release the brake. While it's a clever system, inconsistencies and malfunctions can be frustrating. Your experience with it not activating or struggling to restart points to a few common areas.

Here's what might be going on:

  1. ESS System Conditions:

    • The ESS system has many conditions that must be met for it to activate. These include: sufficient battery charge (both main and auxiliary), engine and transmission at operating temperature, cabin temperature not too extreme (HVAC not running at maximum), hood closed, seatbelt fastened, steering angle, and brake pedal pressure. If any of these are not met, the system will not engage.

  2. Auxiliary Battery:

    • You're absolutely right to suspect the auxiliary battery. The ESS system relies heavily on a dedicated auxiliary battery (usually a smaller AGM battery) to power accessories and ensure a quick restart. If this battery is weak or failing, the ESS system will either not activate, or it will struggle with restarts. This is a very common cause of ESS issues in vehicles equipped with the system.

  3. Sensors and Software:

    • Faulty sensors (e.g., battery current sensor, hood latch sensor) or a software glitch in the Powertrain Control Module (PCM) or Body Control Module (BCM) can also cause erratic ESS behavior. Sometimes, a software update is needed.

  4. When to See a Shop:

    • Battery Check: Your first step should be to have both your main and auxiliary batteries professionally tested. Many auto parts stores offer this service for free. A failing auxiliary battery is often the simplest fix.
    • Professional Diagnosis: If the batteries test good, or if the issue persists, it's time to visit a Chrysler dealership or a reputable independent shop. They can perform a deeper diagnostic scan to check for fault codes (e.g., P1A04 - ESS Battery Sensor Circuit Malfunction) and identify any sensor or software-related issues. Driving with an ESS system that struggles to restart or stalls can be a safety concern, so address it promptly.
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