P3075 on 2020-2026 Buick Encore GX 1.3L: Engine Coolant Flow Too Low Fixes

What's Unique About the 2020-2026 Buick Encore GX

The 1.3L L3T engine in the Encore GX, like many modern GM engines, uses a sophisticated diagnostic strategy for its cooling system. Instead of just relying on temperature sensors, it actively checks the performance of the coolant pump by measuring its current draw during a self-test. This self-test is sensitive enough to detect issues like air pockets or minor leaks that might not cause immediate overheating but can lead to long-term engine problems. GM has issued specific service bulletins (like 21-NA-257) advising technicians to address leaks and air in the system before suspecting a faulty pump.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• Low coolant level in the reservoir.
• Sweet smell of coolant from the engine bay or under the car.
• Visible coolant leaks (pink/orange fluid) on the ground.
• Engine temperature gauge reading higher than normal, or potential overheating.
• In some cases, reduced engine power message may appear.

Most Likely Causes

1. Low engine coolant level due to a leak 🔴 High Probability Modern cooling systems have many plastic components and connection points that can develop leaks over time. Common leak points on the Encore GX and its platform-mate, the Chevy Trailblazer, include heater hoses, radiator connections, and the water pump housing.
   How to confirm: Visually inspect the coolant reservoir. If it's low, perform a cooling system pressure test to locate the source of the leak. Check around hoses (especially heater hoses near the firewall), the radiator, and the water pump for signs of orange/pink Dex-Cool residue.
   Typical fix: Repair the identified leak (e.g., replace a faulty hose or gasket), then refill and bleed the cooling system according to the manufacturer's procedure.
   Est. part cost: $10-$300 depending on the source of the leak (e.g., a hose vs. a radiator).
2. Air trapped in the cooling system 🟡 Medium Probability This often occurs after the cooling system has been serviced (e.g., coolant flush, hose replacement) or if a small leak has allowed air to enter over time. These systems can be difficult to bleed completely without the correct vacuum-fill tool and procedure.
   How to confirm: This is often diagnosed after confirming the coolant level is correct but the code persists. The service procedure itself is the confirmation. A technician may use a scan tool to run the coolant pump bleed procedure.
   Typical fix: Perform the GM-specified Cooling System Draining and Filling procedure, which includes steps for bleeding the air out. This may require a vacuum-fill tool for best results. A scan tool may also be needed to activate the electric coolant pump to purge air.
   Est. part cost: $20-$40 for a jug of ACDelco DEX-COOL coolant.

Rare But Worth Checking

• Faulty Engine Coolant Pump: GM Technical Service Bulletins explicitly state to NOT replace the pump unless all other steps have been taken. This should only be considered if the code returns after a verified leak repair and proper system bleeding. TSB 21-NA-257 states that if the vehicle returns for a second time with P3075 after the initial repair, the pump should be replaced.
• Engine Control Module (ECM) Software Anomaly: An older TSB for other GM models (19-NA-149) mentioned an available software update to correct the diagnostic's sensitivity. While less likely for the Encore GX covered by the newer TSB 21-NA-257, it's a possibility a dealer would investigate, especially on early 2020 models.

Diagnosis Steps

1. Check the engine coolant level in the reservoir. If it is low, top it off with the correct DEX-COOL type coolant.
2. Scan the ECM for any other stored trouble codes.
3. Perform a thorough visual inspection of the engine bay for any signs of coolant leaks (stains, drips, or residue), paying close attention to heater hoses, the radiator, and water pump area.
4. If a leak is not obvious, perform a cooling system pressure test to find the source of the coolant loss.
5. Repair any leaks found during the pressure test.
6. Once all leaks are repaired, perform the manufacturer-specified cooling system draining, filling, and bleeding procedure. This is critical to remove all trapped air. A vacuum-fill tool is highly recommended.
7. Using a capable scan tool (like the GDS), you may need to run the 'Engine Coolant Pump Learn' or 'Bleed' function to prime the pump and purge remaining air.
8. Clear the P3075 trouble code using a scan tool.
9. Drive the vehicle to allow the engine to reach operating temperature and to allow the P3075 diagnostic to run again. Confirm with a scan tool that the test has run and passed.
10. If the code does not return, the repair is complete. If it returns, and you are certain the system is free of leaks and air, the coolant pump itself may be the issue.

Parts You'll Likely Need

• Engine Coolant and Antifreeze (DEX-COOL) (OEM #12346290 (ACDelco 10-101)) — Required to refill the system after repairing a leak and bleeding out air.
  Trusted brands: ACDelco
  OEM price range: $25-$35
  Aftermarket price range: $20-$30
• Cooling System Hoses or Gaskets — These are common sources of leaks that trigger the P3075 code. The specific part needed will be identified during the pressure test. Heater hoses are a frequently cited failure point.
  Trusted brands: ACDelco, Gates
  OEM price range: $30-$150
  Aftermarket price range: $15-$80

Related Codes That Often Appear With This One

• P06DD - Engine Oil Pressure Control Solenoid Valve Stuck Off
• P0299 - Turbocharger/Supercharger Underboost
• P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-257: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3075 Set. This is the primary document for this issue, confirming the cause is low coolant or air and providing the correct diagnostic procedure. It covers a wide range of GM vehicles with 1.3L, 2.0L, and 2.7L engines.

Platform-Specific Known Issues

• GM issued Technical Service Bulletin #21-NA-257 specifically for this code on the 2020-2022 Encore GX (among other vehicles). The bulletin outlines the diagnostic procedure, emphasizing that the cause is likely low coolant or air in the system, and warns against prematurely replacing the coolant pump.
• A case involving a 2022 Chevrolet Trailblazer (a platform mate) with code P3075 also showed codes P06DD and P0299, indicating a coolant leak that led to other system faults.

Mechanic-Grade Diagnostic Values

• Electric Coolant Pump Diagnostic Test — expected: The ECM commands the pump to ~4000 RPM for 15 seconds and measures the AC current draw. A specific amperage range is not published, but a healthy, full cooling system provides proper resistance.. Failure: The measured AC current is lower than the expected range, indicating the pump is spinning too freely due to air pockets or low coolant.

Scan Tool Commands That Help

• GDS2 (or equivalent professional scanner): Cooling System Service Bleed Procedure — After refilling the cooling system to electronically run the coolant pump(s) and purge trapped air from all circuits, which is difficult to do manually.
• GDS2 (or equivalent professional scanner): Engine Cooling Control Valve Learn — After replacing the coolant flow control valve / thermostat assembly to calibrate the new component with the ECM.
• GDS2 (or equivalent professional scanner): Diagnostic Test Status Check — After repairs, to verify that the P3075 intrusive diagnostic test has run and passed during the current drive cycle before returning the vehicle to the customer.

Wiring & Ground Locations

• Main Engine Ground — Part of the main negative battery cable harness, located at the left front of the engine block.. A poor engine ground can cause incorrect electrical readings across multiple components, including the current draw measurement for the electric coolant pump, potentially leading to a false P3075 code.
• G103 — Typically located on the cowl in the engine compartment (above the brake booster) or on the frame rail on other GM vehicles.. This is a major chassis and module ground point. While not directly linked to P3075 in documents, a poor connection at G103 is known to cause widespread, difficult-to-diagnose electrical issues and is worth inspecting if primary diagnostics fail.

Real Owner Repair Stories

• GM TSB PIT6494 for 2023-2026 Chevy Colorado / GMC Canyon (2023-2026 Chevrolet Colorado / GMC Canyon (different vehicle, but same GM era and P3075 code)) — Low coolant level, visible coolant leak, and Malfunction Indicator Lamp with DTC P3075.
  ❌ Tried (didn't work) Initially suspecting a faulty radiator or a loose hose clamp.
  ✅ What actually fixed it The root cause was a degraded seal inside the upper radiator hose quick-connect fitting. The fix was to replace the entire radiator inlet hose assembly (GM Part Number 86518091).
• Reddit user King_beefer (2021 Vauxhall Insignia (European GM vehicle)) — Low coolant warning followed by Check Engine Light with code P3075.
  ❌ Tried (didn't work) Temporarily clearing the light by adding coolant.
  ✅ What actually fixed it The owner confirmed the vehicle had an active coolant leak and concluded this was the cause of the recurring code, aligning with TSB guidance.

Model Year Variations Within This Range

• 2024-2026: The Buick Encore GX received a significant exterior and interior facelift for the 2024 model year. However, the 1.3L L3T powertrain and its associated cooling system were carried over without major changes, so the causes and diagnostic procedures for P3075 remain the same as for the 2020-2023 models.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Brake Booster Failure / Hard Pedal 🔴 High — Common enough to trigger a recall (A202307260) on 2020-2021 models. Owners report a hard brake pedal and increased stopping distance. (Ref: Recall A202307260 / NHTSA 20V-599)
• Mass Airflow (MAF) Sensor/Harness Faults 🟠 Medium — Owners may experience 'Reduced Engine Power' messages and codes like P0101, P0102, or U060F. GM issued an Engineering Information bulletin (PIE0682) to investigate broken wires in the harness leading to the MAF sensor. (Ref: PIE0682, TSB 22-NA-008)
• Fuel Smell from Leaking Fuel Rail 🔴 High — Affects 2020-2021 models with the 1.3L L3T engine. A strong fuel odor may be present due to a leak at the fuel rail, posing a fire risk. (Ref: TSB PIP5765)
• Slow Cabin Heat-Up in Cold Weather 🟡 Low — Some owners report the engine is slow to produce cabin heat in very cold temperatures. GM considers this a normal characteristic of the small, efficient engine. (Ref: TSB 20-NA-024)
• Squeaking Brakes 🟡 Low — A TSB was issued for 2020 models due to customer complaints of brake squeal, though it was not considered a safety issue. (Ref: TSB mentioned in owner forums for 2020 models.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: Used parts are generally not recommended for this repair, as the common failures are wear items. A used coolant reservoir (surge tank) is acceptable if it is free of cracks. A used electric coolant pump could be considered ONLY if it is from a very low-mileage donor vehicle (<30,000 miles) and the cost savings are significant.

Donor-vehicle mileage cap: roughly under 30000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a used coolant pump, inspect the electrical connector for any signs of corrosion or moisture.
• Check the pump housing for any hairline cracks or evidence of past leaks (white or pink residue).
• Ensure all mounting points are intact.

OEM-only on this vehicle (don't cheap out):

• Coolant Flow Control Valve / Thermostat Assembly: This is a complex electronic component. Aftermarket versions may not calibrate or function correctly with the factory ECM; using an OEM part is strongly advised.
• Electric Coolant Pump: While some high-quality aftermarket options may exist, cheap replacement pumps often have a much shorter service life (e.g., 30,000 miles vs. 100,000+ for OEM). Given the labor involved, an OEM or top-tier OEM-supplier part is the safest investment.

Brands owners have reported issues with on this vehicle:

• Unbranded or exceptionally low-cost electric water pumps and thermostat assemblies from online marketplaces.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P06DD — Observed alongside P3075 in platform-mate vehicles when a coolant leak leads to broader engine management faults.
• P0299 — A turbocharger underboost code that can appear in conjunction with P3075 during a coolant leak event.
• P0101 — A MAF sensor performance code that may appear on this vehicle platform due to harness faults (TSB 22-NA-008), sometimes coinciding with 'Reduced Engine Power' symptoms.
• P0102 — MAF sensor circuit low frequency code related to the same wiring harness issues identified in GM Engineering Information PIE0682.
• U060F — A communication code related to the MAF sensor harness that can be triggered by the same broken wire issues seen on the Encore GX platform.

Frequently Asked Questions