U0672 on 2019-2024 Chevy Silverado 1500: Causes and Fixes for Coolant Pump Communication Loss

What's Unique About the 2019-2024 Chevrolet SILVERADO 1500

This issue is particularly well-documented on the Silverado 1500 and its platform mates (GMC Sierra, Chevy Colorado) equipped with the 2.7L L3B engine, which uses an electronically controlled main water pump instead of a traditional belt-driven one. General Motors has issued multiple Technical Service Bulletins (TSBs) that point directly to wiring connection problems at the pump or its fuse block as the primary culprit. This is a key piece of information, as many technicians or DIYers might otherwise replace the expensive pump assembly when only a simple wiring or fuse block fix is needed.

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 quickly into the red or showing an overheating warning.
• Message on the driver information center like 'Engine Power Reduced' or 'Idle Engine'.
• Vehicle may enter 'limp mode' with reduced acceleration to protect the engine.
• Loss of cabin heat, as hot coolant may not be circulating through the heater core.
• Cooling fans may run at high speed continuously as a protective measure.

Most Likely Causes

1. Poor connection at the Electric Engine Coolant Pump 🔴 High Probability → Shop Engine Water Pump GM Technical Service Bulletins #PIP5863B and #PIP5863C specifically identify this as a known issue. The connector can suffer from contamination, poor terminal tension, or corrosion.
   How to confirm: Visually inspect the wiring harness and connector at the electric coolant pump. Check for any signs of damage, dirt, or loose pins. Per TSB guidance, simply unplugging and securely replugging the connector ('cycling the connection') can sometimes resolve the issue. GM allocates 0.3 labor hours under warranty just for this check (Labor Op 4088838).
   Typical fix: Clean the connector terminals and apply dielectric grease. If terminals are loose or damaged, the connector pigtail may need to be replaced. Some owners have found the pigtail is not sold separately by GM, requiring an aftermarket part.
   Est. part cost: $0-$50
2. Failed or poor connection at the battery-top fuse block 🟡 Medium Probability → Shop Vehicle Battery The electric coolant pump is a high-draw component with a dedicated, high-amperage fuse (typically 40A or 80A) located in the fuse block on top of the battery. Real-world mechanic reports show that a poor internal connection within this fuse block can cause a significant voltage drop or an open circuit, triggering U0672 even if the fuse isn't blown. In many cases, the fuse itself is not separately serviceable.
   How to confirm: Locate the battery-mounted fuse block. Inspect the fuse designated for the engine coolant pump. A visual inspection may not be enough; a voltage drop test across the fuse while wiggling it is the most effective diagnostic method. If a large voltage drop occurs, the block is faulty.
   Typical fix: Replace the entire battery-top fuse block assembly. 🎬 See this walkthrough on how to replace the battery fuse block. In many documented cases, attempting to replace just the fuse is not possible, as it is integrated into the block.
   Est. part cost: $50-$150
3. Failed Electric Engine Coolant Pump 🟡 Medium Probability → Shop Engine Water Pump The pump assembly contains an integrated control module. This electronic module can fail, causing it to stop communicating. GM had a customer satisfaction program (N202320510) for some 2020-2021 models due to incorrectly manufactured printed circuit boards inside the pump that could cause failure. This program expired on December 31, 2022. A short circuit within the pump can also cause the high-amperage fuse in the battery block to blow.
   How to confirm: If the wiring, connector, and fuse block are all confirmed to be good, and power and ground are present at the connector, the pump assembly itself is the likely point of failure. A shorted pump can also cause the fuse in the battery block to blow repeatedly.
   Typical fix: Replace the entire electric engine coolant pump assembly. This requires draining the cooling system.
   Est. part cost: $250-$500

Rare But Worth Checking

• Damaged engine wiring harness: → Shop Engine Wiring Harness While the connector is the most common wiring failure point, the harness itself can be chafed or damaged elsewhere, particularly where it routes near the engine or chassis components. TSB #PIT5677A lists U0672 among 🎬 Watch: Mechanic explains LIN bus issues and harness routing problems. many codes that can be caused by harness chaffing on 2019 models.
• Failed Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is extremely rare. The ECM is the 'brain' sending the commands, but it is highly unlikely to fail in a way that only affects communication with a single component. All other causes should be exhausted before considering the ECM.

Diagnosis Steps

1. Read all Diagnostic Trouble Codes (DTCs) from the ECM to see if other communication or circuit codes are present, such as U1345 or P2B85.
2. Locate the battery-top fuse block. Inspect the specific fuse for the electric coolant pump (often a 40A or 80A fuse).
3. Perform a voltage drop test across the pump fuse. Connect a multimeter and, with the system on, gently wiggle the fuse and its connecting wires. A voltage reading above a few hundred millivolts indicates a bad connection inside the fuse block.
4. If the fuse block is good, locate the electric coolant pump on the engine. Carefully inspect the 4-way electrical connector and the surrounding wiring for any signs of corrosion, damage, or loose pins.
5. Disconnect the connector, clean it with electrical contact cleaner, and apply a small amount of dielectric grease before reconnecting it securely. This is known as 'cycling the connection'. Clear the codes and see if U0672 returns.
6. If the code persists, use a multimeter to check for proper voltage and ground at the pump's electrical connector with the ignition on. This confirms the circuit integrity from the fuse block to the pump.
7. If the fuse block, wiring, and connector are all good, and power/ground are confirmed at the connector, the electric coolant pump assembly is the most likely cause of the failure and should be replaced.

Parts You'll Likely Need

• Electric Engine Coolant Pump (OEM #12712271, 12706665) — This is the component that fails if the wiring and fuse are confirmed to be good. The internal electronics fail, causing the loss of communication.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $300-$500
  Aftermarket price range: $250-$400
• Battery-Top Fuse Block Assembly — A poor internal connection or a short circuit in the pump can damage this non-serviceable fuse block, cutting off power and communication. It must be replaced as a complete unit.
  Trusted brands: GM Genuine Parts
  OEM price range: $50-$150
• Electric Coolant Pump Connector Pigtail (OEM #ACDelco PT2923 (example, verify fitment)) — If the connector housing or terminals are damaged, a pigtail is needed to splice in a new connector. This part may not be available directly from GM, requiring an aftermarket solution.
  Trusted brands: ACDelco, Dorman, Connection Solutions
  OEM price range: $30-$50
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• U1348 — This code indicates a fault on the LIN Bus communication network. The electric coolant pump communicates on this network, so a fault with the pump or its wiring can trigger both codes.
• P2B85 — This code relates to 'Engine Coolant Pump Speed Deviation'. It can be set in conjunction with U0672 if the pump fails internally, as noted in GM's customer satisfaction program N202320510.
• 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

• PIP5863B / PIP5863C: Advises inspection of the Electric Engine Coolant Pump connection for a U0672 code.
• PIT5677E / PIT5677A: Lists U0672 as one of many potential codes that can result from engine wire harness chaffing.
• N202320510: Customer Satisfaction Program for faulty water pumps in certain 2020-2021 models.

Platform-Specific Known Issues

• TSB #PIP5863B/C: GM explicitly advises technicians to inspect the electric engine coolant pump connection for issues before performing other diagnostics. It recommends cycling the connector and clearing the code. GM even created a unique labor operation (4088838) and time (0.3 hr) just for this inspection, indicating its high frequency.
• Customer Satisfaction Program #N202320510: Issued for certain 2020-2021 models, this program addressed incorrectly manufactured printed circuit boards inside the water pump that could cause failure. The no-charge replacement offer expired on December 31, 2022.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at rest) — expected: Approx. 11-12 Volts (1V less than system voltage). Failure: Voltage significantly lower than 11V, 0V, or stuck high at battery voltage with no communication toggling.
• LIN Bus Voltage (communicating) — expected: Toggling between approx. 11-12V (max) and approx. 1V (min).. Failure: A steady voltage with no toggling indicates a lack of communication from either the master (ECM) or slave (pump) module.
• Ground Resistance at Pump Connector — expected: Below 0.1 Ω. Failure: Resistance higher than 0.1 Ω indicates a poor ground connection, which can cause communication errors.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Engine > Output Controls > Low Temperature Loop Coolant Pump — This bidirectional command allows a technician to command the electric coolant pump on at various speeds (10-100%). It is used to verify if the pump physically runs when commanded, helping to distinguish between a wiring/communication issue and a completely dead pump.
• GDS2 (GM Global Diagnostic System 2): Hybrid/EV Battery Pack Coolant Pump Bleed Procedure — While the name is specific to Hybrid/EVs, a similar engine coolant system bleed procedure exists for the L3B. After replacing the electric coolant pump, air must be purged from the system. The GDS2 tool is used to actuate the pump in a specific sequence to bleed air out. Failure to do this can cause overheating and DTCs even with a new pump.

Wiring & Ground Locations

• K61 — This is the GM RPO code and schematic identifier for the Electric Engine Coolant Pump Control Module, which is integrated into the pump assembly.. U0672 specifically means 'Lost Communication With K61'. All diagnostics are centered on re-establishing the communication link between the ECM and this module.
• X327 (example, verify on specific vehicle) — The 4-pin electrical connector at the Electric Engine Coolant Pump itself, located on the lower left side of the engine.. This is the most common point of failure. TSB #PIP5863B/C directs technicians to inspect and cycle this specific connector first. The LIN bus communication wire is one of the four pins in this connector.
• LIN Bus Circuit — A single wire running from a pin at the Engine Control Module (ECM) to a pin at the K61 pump connector (X327).. This single wire carries all the command and status information. A short to ground or an open in this wire will immediately set U0672. The ECM and the pump module each supply their own reference voltage to this circuit.

Real Owner Repair Stories

• YouTube video by 'Casí que motor' (2022 Chevrolet Silverado 1500) — Check Engine Light with code U0672.
  ❌ Tried (didn't work) The diagnosis immediately pointed to the pump.
  ✅ What actually fixed it The electric water pump had an internal short to ground, which caused the 80A 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, as the fuse was not separately serviceable.

OEM Part Supersession History

• 12706665 → 12712271 — Part revision or manufacturer change.
• 12712271 → 12746198 — Part revision or manufacturer change.
• 12718538 → 12738952 — Part revision or manufacturer change.
  Heads up: Part number 12738952 is listed as a replacement for a long list of previous numbers, including 12690125, 12694321, 12706665, 12712271, and 12718538, indicating it is likely the latest revision for this application.

Model Year Variations Within This Range

• 2022+: For the 2022 model year refresh, the 2.7L L3B engine was updated to a 'High-Output' version with a stronger block and a significant torque increase from 348 lb-ft to 430 lb-ft. While the core cooling system design, including the electric water pump, remained the same, the engine control module (ECM) tuning is different. This does not change the diagnosis for U0672 but is a key difference in the platform.