U0672 on 2021-2024 Buick ENVISION: Lost Communication with Coolant Pump Causes and Fixes

What's Unique About the 2021-2024 Buick ENVISION

The 2021-2024 Buick Envision uses a sophisticated electronically controlled water pump as part of its Active Thermal Management system, rather than a simple belt-driven pump. This system allows for precise temperature control by varying coolant flow but introduces a point of failure in the communication network. General Motors has issued specific Technical Service Bulletins (TSBs) for this exact code on this platform and its platform mates, acknowledging that a poor electrical connection is a common cause, sometimes more so than outright pump failure.

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 overheating or temperature gauge rising rapidly.
• Loss of cabin heat.
• Engine may enter a reduced power 'limp mode' to protect itself.
• Steam coming from under the hood if the engine is severely overheating.

Most Likely Causes

1. Poor Electrical Connection at Coolant Pump 🔴 High Probability This is a widely known issue documented by GM in Technical Service Bulletins PIP5863B and PIP5863C for this specific vehicle, engine, and its platform mates.
   How to confirm: Visually inspect the 4-wire electrical connector on the electric coolant pump for corrosion, contamination, loose pins, or damage. The TSB recommends unplugging and reconnecting the connector ('cycling the connection') to see if it resolves the intermittent fault.
   Typical fix: Clean the connector terminals 🎬 Watch: How to identify and repair rust inside the connector and ensure a secure connection. If the connector or wiring is damaged, it will need to be repaired or replaced with a pigtail kit (GM Part No. 19371209). GM authorizes a 0.3-hour labor operation (Code 4088838) just for cycling the connector under warranty.
   Est. part cost: $0-$50
2. Failed Electric Engine Coolant Pump Module 🟡 Medium Probability The pump contains integrated electronics that can fail, causing a short or an open circuit that stops communication on the LIN bus. A history of manufacturing defects on earlier versions of this pump for the LSY engine has been noted by GM.
   How to confirm: If the wiring and connector are in perfect condition and the code returns immediately after clearing, the pump module itself is likely faulty. An advanced scan tool may be able to directly test the pump's response but will likely show no communication.
   Typical fix: Replace the entire electric coolant pump assembly. The module is integrated with the pump.
   Est. part cost: $150-$400
3. Blown Fuse ⚪ Low Probability An internal short circuit in the water pump can cause a high current draw, blowing the fuse that protects the circuit. On related GM trucks with a similar setup, this is a large 80-amp fuse located in the battery-top fuse block.
   How to confirm: Check the fuse box, particularly the one on top of the battery, for the fuse corresponding to the electric water pump. A visual inspection or continuity test will confirm if it's blown.
   Typical fix: Replace the blown fuse. However, a blown fuse is usually a symptom of a larger problem (like a shorted pump), so the root cause must be found and fixed or the new fuse will also blow.
   Est. part cost: $5-$20

Rare But Worth Checking

• Wiring Harness Damage: The wiring harness leading to the pump could be chafed or damaged somewhere other than the connector. This can happen due to improper routing, vibration, or contact with other engine components.
• Faulty Engine Control Module (ECM): While rare, the ECM itself can develop a fault on the communication bus, preventing it from talking to the coolant pump module. This should only be considered after all other possibilities have been exhausted.

Diagnosis Steps

1. Verify the code U0672 is present using an OBD-II scanner. Note any other codes like U1348 or P26BB.
2. Turn the vehicle off. Locate the electric engine coolant pump on the lower-left (driver's) side of the engine.
3. Carefully inspect the 4-wire electrical connector and the first few inches of wiring going to the pump. Look for any signs of green or white corrosion, melted plastic, backed-out pins, or physical damage.
4. As per GM TSB #PIP5863C, disconnect the connector, inspect the pins for good tension, and reconnect it firmly. This is known as 'cycling the connection'.
5. Check the fuse for the electric coolant pump, paying close attention to the large fuses in the battery-top fuse block if applicable. If it is blown, investigate for a short circuit before replacing it.
6. Clear the trouble code using the scanner.
7. Start the engine and let it run to see if the code returns. If it does not return, the issue was likely a poor connection.
8. If the code returns immediately, and the wiring appears to be in good condition, the electric coolant pump assembly is the most likely failed component.
9. If possible, use an advanced scan tool to attempt to directly command the pump on and off to confirm it is unresponsive.

Parts You'll Likely Need

• Electric Engine Coolant Pump Assembly (OEM #12738953) — This is the component that fails if the issue is not a simple wiring connection. The control module is integrated into the pump assembly. This part number supersedes the older 12724522.
  Trusted brands: ACDelco (OEM)
  OEM price range: $250-$400
  Aftermarket price range: $150-$250
• Coolant Pump Wiring Pigtail Kit (OEM #19371209) — If the connector itself is corroded, melted, or damaged, replacing the pigtail is necessary instead of replacing the entire engine harness.
  Trusted brands: GM Genuine Parts
  OEM price range: $30-$60
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• U1348 — This code indicates a fault on the LIN Bus where the coolant pump communicates. A problem with the pump module can disrupt the entire bus, causing both codes to appear. A Reddit user with a 2022 Blazer 2.0L reported these two codes together.
• P26BB — This code relates to 'Engine Coolant Pump Speed Deviation'. It may be set along with U0672 if the pump fails internally and the ECM detects that the pump speed is not what is being commanded.
• U1345 — This code indicates a fault on 'Engine Control Module LIN Bus 1'. It is often seen with U0672 when a wiring or fuse block issue disrupts the communication line.

Technical Service Bulletins (TSBs) & Recalls

• PIP5863C: Advises technicians to inspect the Electric Engine Coolant Pump connection for issues and to clear the code to see if it resets. This is the latest version.
• PIP5863B: An earlier version of the same bulletin, also pointing to a potential connection issue as the cause for U0672. This TSB explicitly lists the affected models including the Envision, Blazer, Acadia, and various Cadillacs.

Platform-Specific Known Issues

• GM has issued Technical Service Bulletins (PIP5863B and PIP5863C) specifically for code U0672 on the 2021-2024 Envision and its platform mates with the 2.0L LSY engine. The bulletins advise technicians to first inspect and cycle the electrical connection at the pump before replacing parts, as a poor connection is a known cause.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at pump connector, communication wire) — expected: Toggling between approx. 1V (min) and 12V (max) when communicating. A steady 11-12V indicates the bus is at rest (no communication).. Failure: A steady voltage significantly different from 12V, or no voltage, can indicate a short to ground or an open circuit. A steady voltage that is not toggling can indicate a short to power.
• Coolant Pump Power Supply Voltage — expected: Steady 12V (or battery voltage) with ignition on.. Failure: Fluctuating or no voltage suggests a problem with the fuse or power feed wiring.
• Coolant Pump Ground Circuit Resistance — expected: Below 0.1 Ω when measured between the ground pin at the connector and a known good chassis ground.. Failure: High resistance (OL) indicates an open ground circuit.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Coolant Pump Bleed Procedure — This procedure is required after replacing the coolant pump or opening the cooling system to purge all air. Failure to do so can cause overheating, DTCs, and noise even with a new part.
• GDS2 (GM Global Diagnostic System 2): Data Bus Diagnostic Tool - Message Monitor — For intermittent communication issues, this tool can passively monitor the LIN bus with the vehicle off to see if the coolant pump module is staying 'awake' and causing a battery drain, which can be a symptom of an internal module fault.

Wiring & Ground Locations

• G59 — The electrical connector on the Electric Engine Coolant Pump assembly, located on the bottom-left (driver's) side of the engine block.. This is the primary connection point for power, ground, and the LIN bus communication wire. TSB PIP5863C identifies a poor connection at G59 as the most common cause of U0672.
• Battery Tray Support Bracket Harness Chafe Point — The engine wiring harness may rub against the sharp edges of the battery tray support bracket.. TSB 23-NA-074 identifies this as a potential chafe point on platform-mate vehicles (Blazer, Acadia, XT5) that can damage wiring and cause a wide range of communication DTCs, including U0672.
• Battery-Mounted Fuse Block — Directly on top of the vehicle's positive battery terminal.. This block contains the main power fuse (e.g., 40A or 80A) for the electric coolant pump. An internal short in the pump can blow this fuse, which is often integrated into the block and not separately serviceable.

Real Owner Repair Stories

• YouTube - Casí que motor (2022 Chevrolet Silverado 1500 (related powertrain)) — Check Engine Light with code U0672.
  ❌ Tried (didn't work) Initial diagnosis pointed directly to the pump, but replacing only the pump would not have solved the entire issue.
  ✅ What actually fixed it The electric water pump had an internal short to ground. This short caused the 80-amp fuse in the battery-top fuse block to blow. The final repair required replacing both the electric water pump and the entire battery-top fuse block assembly because the fuse was not serviceable on its own.

OEM Part Supersession History

• 12724522, 55506790, 55508939, 55510113, 55515497 → 12738953 — Standard part evolution for improved reliability or manufacturing process changes.