Low Coolant or Air Trapped in Engine Cooling System

An illuminated Check Engine MIL and DTC P3075 (Engine Coolant Flow Too Low) may be set in the Engine Control Module (ECM) on some 2019-2022 XT4, Blazer, Silverado 1500, Sierra 1500; 2019-2021 Malibu; 2020-2022 Encore GX, CT4, CT5, XT5, XT6, and Acadia; and 2021-2022 Trailblazer models equipped with the 1.3L engine (RPO L3T), 2.0L engine (LSY) or 2.7L engine (RPO L3B). These conditions may be caused by low coolant or air trapped in the engine cooling system.

TIP: For 2019 MY vehicles equipped with the 2.7L engine, refer to Bulletin #19-NA-149 to verify the vehicle has the most current level of software.

If these conditions are found, do not replace the coolant pump. Begin diagnosis by pressure testing the cooling system using the EN-24460-A Cooling System Pressure Tester to check for any coolant leaks. (Fig. 10) Repair any leaks to the cooling system following the procedures in the appropriate Service Information.


Fig. 10


Once any coolant leaks have been repaired, follow the Cooling System Draining and Filling procedure in the appropriate Service Information to fill and bleed the cooling system. Once the engine is started after the coolant service fill procedure, DTC P3075 may reset until all the air is properly purged from the cooling system. At this point, codes should be cleared, the engine should be at operating temperature and the vehicle road tested to completely purge any remaining air from the cooling system.

After a road test, clear any DTCs and operate the vehicle under the conditions for running DTC P3075 following the Service Information procedures. DTC P3075/P3076 can detect coolant flow-based failures. The intrusive diagnostic test will run once per ignition cycle if all enable conditions are met. The coolant pump will run at roughly 4,000 rpm for 15 seconds and the pump motor AC current should be within the expected range. The coolant pump AC current feedback will be lower if the cooling system is leaking or low on coolant. Use GDS to confirm that DTC P3075 test has run and passed in the current drive cycle.

If the vehicle returns a second time with DTC P3075 set, replace the coolant pump assembly. (Fig. 11) Parts will be returned to the Warranty Parts Center.


Fig. 11


For additional information, refer to Bulletin #21-NA-257.


– Thanks to Marcus Plant

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