U0672 on 2020-2024 Chevrolet Blazer: Causes and Fixes for Coolant Pump Communication Loss

What's Unique About the 2020-2024 Chevrolet BLAZER

The 2020-2024 Chevrolet Blazer, particularly models with the 2.0L LSY turbo engine, uses an electronically controlled water pump as part of its Active Thermal Management system. This system, which does not use a traditional wax-pellet thermostat, allows the ECM to precisely manage coolant flow for performance and efficiency. This design makes it susceptible to communication-based failure codes like U0672, which would not occur on an engine with a simple belt-driven water pump. General Motors has issued specific service bulletins acknowledging this communication issue across multiple vehicles that use the LSY engine.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• Engine temperature gauge rising rapidly into the red zone.
• Engine overheating warning light or message on the dashboard.
• Loss of cabin heat, with vents blowing cold air.
• Engine may enter a reduced power or "limp mode" 🎬 Watch: Diagnosing U0672 and reduced power on a GM engine to prevent damage.
• Cooling fans running at maximum speed constantly.

Most Likely Causes

1. Poor Connection at Electric Engine Coolant Pump 🔴 High Probability GM Technical Service Bulletins #PIP5863B and #PIP5863C specifically identify a potential connection issue at the pump as the primary cause for this code on the 2020-2024 Blazer. The bulletins advise technicians to check for wiring contamination, poor terminal tension, crimp or lock issues before replacing parts.
   How to confirm: Visually inspect the 4-pin electrical connector (X327) on the electric coolant pump for any signs of damage, corrosion, or loose pins. As per the TSB, disconnect and reconnect the connector to ensure it is seated properly (a process called 'cycling the connector'), then clear the code and see if it returns. This simple action often resolves the problem.
   Typical fix: Clean the connector terminals with electrical contact cleaner and apply dielectric grease. If terminals are damaged, the connector pigtail may need to be replaced. In many cases, simply cycling the connector resolves the issue, a repair for which GM even has a specific warranty labor operation (4088838) that takes 0.3 hours.
   Est. part cost: $0-$50
2. Failed Electric Engine Coolant Pump / Control Module 🟡 Medium Probability The control module is integrated into the pump assembly. An internal electronic failure in this module, such as on its printed circuit board, will stop communication and require replacement of the entire pump unit. GM has a history of electronic faults with this pump design, as noted in customer satisfaction program N202320510 for a similar issue on other 2020-2021 models.
   How to confirm: If the wiring and connector are confirmed to be good (including power, ground, and LIN bus signal checks with a multimeter), the pump assembly itself is the likely point of failure. A technician with a GM GDS2 scan tool can try to command the pump on to verify if it responds.
   Typical fix: Replace the entire electric engine coolant pump assembly. This involves draining the cooling system, replacing the pump, and refilling/bleeding the system with DEX-COOL coolant.
   Est. part cost: $572-$801
3. LIN Bus Wiring Fault ⚪ Low Probability GM has noted in other TSBs, like 21-NA-149, that engine wire harnesses can chafe against engine components, such as the camshaft carrier cover, potentially causing shorts or open circuits on various wires, including the LIN bus wire for the coolant pump.
   How to confirm: Check for continuity and shorts on the LIN bus wire (typically a single wire) between the ECM and the coolant pump connector. This is an advanced diagnostic step requiring a wiring diagram and multimeter. A visual inspection of the harness routing for any signs of rubbing or damage is also critical.
   Typical fix: Repair the damaged section of the wiring harness and secure it away from any sharp edges or points of contact.
   Est. part cost: $5-$100

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner.
2. Visually inspect the wiring harness and the 4-pin connector at the electric engine coolant pump for any signs of damage, corrosion, or looseness. This is the most common point of failure.
3. As per TSB PIP5863C, disconnect the pump connector, inspect the terminals for contamination or poor tension, and reconnect it firmly.
4. Clear the U0672 code and test drive the vehicle to see if the code returns. If it does not, the issue was likely the connection and the vehicle can be returned to the customer.
5. If the code returns, use a multimeter to check for proper power, ground, and signal on the LIN bus wire at the pump connector. This verifies the integrity of the circuit from the power source to the pump.
6. If using a professional scan tool (like the GM GDS2), attempt to command the coolant pump on and monitor its status to see if it responds.
7. If wiring and signals are confirmed to be good but the pump does not respond, the electric engine coolant pump assembly has likely failed and requires replacement.

Parts You'll Likely Need

• Electric Engine Coolant Pump (OEM #12738953) — The integrated control module within the pump is a common failure point. If the wiring connection is good, the entire pump assembly is the next logical part to replace. This part number is the most current and replaces several older versions.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $572-$801
  Aftermarket price range: $250-$450

Related Codes That Often Appear With This One

• U1348 — This code indicates a fault on LIN Bus 2 or 4. Since the electric coolant pump (G59) communicates on a LIN bus, a fault with the pump or its wiring can lock up the bus and trigger both codes simultaneously.
• P26BB — This code relates to the coolant flow control valve, which works in conjunction with the electric water pump as part of the Active Thermal Management system. A failure in the system can sometimes set both codes.

Technical Service Bulletins (TSBs) & Recalls

• PIP5863C: Malfunction Indicator Lamp (MIL) Illuminated due to a U0672 setting. Advises the technician to perform Electric Engine Coolant Pump connection inspections. To clear the code to see if it resets current. If the code does not reset, release the vehicle to the customer. (Updated March 2024).
• PIP5863B: An earlier version of the same bulletin, also addressing MIL on with U0672 and advising inspection of the coolant pump connection.
• TSB 21-NA-149: While not exclusively for U0672, this bulletin notes that engine wire harness contact with the camshaft carrier cover on 2.7L L3B engines (which share design characteristics) can cause a wide range of DTCs, including U0672, due to chafing.

Platform-Specific Known Issues

• GM has issued Technical Service Bulletin (TSB) PIP5863C and its earlier versions for the 2020-2024 Chevrolet Blazer with the 2.0L LSY engine. It specifically addresses the U0672 code and directs technicians to first inspect the electrical connection at the pump before performing other diagnostics.
• The TSB explicitly states that after checking for harness issues, if simply cycling the connector and clearing the code prevents it from returning, the vehicle should be released to the customer, indicating how common the connection-only fault is.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at rest, key on) — expected: A steady voltage approximately 1 volt less than battery system voltage (e.g., ~11-12V).. Failure: Voltage near 0V may indicate a short to ground. No voltage could be an open circuit.
• LIN Bus Voltage (communicating) — expected: Using a multimeter on MIN/MAX, the voltage should toggle between a max of ~1V below system voltage and a min of ~1V above ground. On an oscilloscope, it will be a square wave pattern.. Failure: A flat line at any voltage indicates no communication. A voltage stuck low suggests the bus is shorted or a module is holding it down.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Coolant Pump Control / Output Control — After verifying wiring integrity, this bidirectional control is used to command the electric coolant pump on and off to determine if the pump's internal control module is responsive. If the pump does not activate when commanded, and power/ground/signal are verified good, the pump assembly has failed.
• GDS2 (GM Global Diagnostic System 2): Hybrid/EV Battery Pack Coolant Pump Bleed Procedure — After replacing the electric coolant pump, this service function must be run to properly bleed air from the cooling system. Failure to perform this procedure can lead to overheating, repeat DTCs, and improper system operation.

Wiring & Ground Locations

• X327 — The 4-pin electrical connector located directly on the G59 Electric Engine Coolant Pump assembly. The pump is situated on the lower-left (driver's) side of the engine block.. This is the primary point of failure identified in GM TSB PIP5863C. Inspecting for terminal tension, corrosion, and proper seating at this specific connector is the first diagnostic step.
• G107 / G108 — Main engine block and radiator support grounds. On similar GM platforms, G107 and G108 are located on the engine block and/or radiator support. A poor engine ground can cause floating voltages and communication errors across multiple components.. While not a primary cause, a loose or corroded main engine ground can create unpredictable electrical issues, including network communication faults like U0672. Verifying these grounds are clean and tight is a good practice during advanced electrical diagnosis.

Real Owner Repair Stories

• Go-Parts.com Repair Database (2020-2024 Cadillac XT5 (shares the 2.0L LSY engine and pump with the Blazer)) — Check Engine Light with code U0672.
  ❌ Tried (didn't work) In some documented cases, cleaning the connector or replacing the pigtail did not provide a permanent solution, and the code returned.
  ✅ What actually fixed it The final and permanent repair was the replacement of the entire electric engine coolant pump assembly. This reinforces the official GM diagnostic path: attempt the TSB-recommended connector cycle first, and if the code returns, replace the pump.

OEM Part Supersession History

• 55506790, 55508939, 55510113, 55515497, 12724522 → 12738953 — Standard part evolution for improved reliability or manufacturing changes.
  Heads up: Part number 12738953 is the latest revision and is backward compatible with the older numbers for the 2020-2024 Blazer with the 2.0L engine.

Model Year Variations Within This Range

• 2023-2024: The Chevrolet Blazer received a mid-cycle refresh for the 2023 model year, which included updated front/rear fascias, new wheel designs, and a larger standard 10-inch infotainment screen. However, the powertrain options, including the 2.0L LSY engine and its associated Active Thermal Management cooling system, were unchanged. Therefore, the causes and fixes for code U0672 remain identical across the entire 2020-2024 year range.