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2021 Encore GX Low Coolant Warning & P0128 Code

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Mike T. · rep 0 · May 22, 3:53 AM · 1 replies · solved · Question

Vehicle: 2021 Buick Encore GX Select

Hi everyone,

My 2021 Buick Encore GX Select, with about 45,000 miles, recently threw a 'Low Coolant' warning on the dash. I checked the reservoir, and it was indeed below the minimum line. I topped it off, but a few days later, the check engine light came on, and I pulled a P0128 code with my OBD scanner.

I'm not seeing any obvious leaks on my driveway, but I'm worried about what this code means. Is it just a faulty thermostat, or could it be something more serious? What kind of coolant should I be using for this model, and is there anything else I should check myself before taking it to a shop?

Any guidance would be super helpful!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:53 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a common issue that can arise with cooling systems. The P0128 code, combined with a low coolant warning, points directly to a problem with your engine's thermostat or the cooling system's ability to reach and maintain optimal operating temperature.

Here's a breakdown and what to do:

  1. Understanding P0128: This code stands for 'Coolant Thermostat (Coolant Temperature Below Regulating Temperature)'. It means the engine's coolant is taking too long to reach its normal operating temperature, or it's not reaching it at all. The most common cause is a thermostat stuck open, allowing coolant to flow freely and preventing the engine from warming up efficiently. Less common causes include a faulty engine coolant temperature (ECT) sensor or low coolant levels.
  2. Coolant Type: For your 2021 Buick Encore GX, you must use DEX-COOL extended-life coolant. It's an orange/pinkish-red color. Using conventional green coolant can lead to corrosion and damage to your cooling system components. Always mix it 50/50 with distilled water if you're buying concentrate.
  3. Troubleshooting Steps:
    • Check for Leaks Again: Even if you don't see puddles, check hoses, radiator, water pump, and the coolant reservoir for any signs of dried coolant residue (often a pinkish crust). A small leak might only show up when the system is under pressure.
    • Thermostat Function: If the upper radiator hose feels cold while the engine is warming up, and then suddenly gets hot, the thermostat is likely working. If it gets hot quickly from a cold start, the thermostat might be stuck open.
    • ECT Sensor: While less common, a faulty ECT sensor can send incorrect temperature readings to the engine control module (ECM), triggering the P0128. This usually requires diagnostic tools to verify.
    • Bleed Air: After topping off coolant, ensure there's no air trapped in the system. Run the engine with the heater on high and the reservoir cap off (or slightly loose) until the engine reaches operating temperature, allowing air bubbles to escape.

When to See a Shop: If you've confirmed no leaks and the P0128 code persists after ensuring proper coolant levels and bleeding, it's highly probable that the thermostat needs replacement. This is a relatively straightforward job for a mechanic. Ignoring a stuck-open thermostat can lead to decreased fuel economy and increased engine wear due to prolonged operation at suboptimal temperatures.

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