LM2 3.0 Duramax: GM Issues Special Coverage for Coolant Control Valve (N252508341)

Release: September 2025 • Bulletin: N252508341 • Applies to (LM2 3.0L Duramax):Chevrolet: Silverado 1500 (2021–2022), Suburban (2021–2023), Tahoe (2021–2023)GMC: Sierra 1500 (2021–2022), Yukon (2021–2023)Cadillac: Escalade (2021–2023)

https://www.youtube.com/watch?v=GzAYAcCUWz0

At a Glance

• What happened: GM announced a Special Coverage for potential engine coolant control valve failures that fail an onboard vehicle diagnostic test.

• Symptoms called out by GM: MIL/Check Engine Light and a diagnostic trouble code; in some cases cooling fans run after key-off.

• Coverage window: 15 years or 150,000 miles from the original in-service date (whichever comes first), regardless of ownership.

• The fix: If diagnostics confirm the valve, dealers replace the engine coolant control valve at no charge under this coverage.

• Service contracts: Repair orders on/after Sept 16, 2025 are submitted under this Special Coverage; before Sept 16, 2025, submit to the Service Contract provider.

• Reimbursement: Owners who previously paid for this repair may request reimbursement per the bulletin’s instructions.

What “Special Coverage” Means (Plain English)

This is not a recall and not a blanket part swap. Special Coverage functions like an extended warranty on a specific part when a specific condition occurs. GM covers the repair only if diagnostics show the coolant control valve is the root cause of the failure condition the bulletin describes. Inside the 15-year/150k-mile window, the valve replacement is no charge to the customer.

Note: The bulletin language references a failure of an onboard vehicle diagnostic test. GM’s text does not list specific DTCs; in field reports for the LM2/LZ0 platform, owners commonly encounter P1098 or P26BB when this system is involved. Treat those as examples, not as the bulletin’s official list.

Models Covered (LM2)

• Chevrolet: Silverado 1500 2021–2022, Suburban 2021–2023, Tahoe 2021–2023

• GMC: Sierra 1500 2021–2022, Yukon 2021–2023

• Cadillac: Escalade 2021–2023

To confirm eligibility on a specific vehicle, dealers should check IVH → Applicable Warranties in GM’s Global Warranty Management system.

Symptoms & What to Watch For

• MIL/Check Engine Light with a valve-related diagnostic result

• Engine cooling fans that continue to run after shutdown

If you see these symptoms, schedule diagnostics to verify whether the coolant control valve is at fault.

The Fix (Dealer Procedure Summary)

• Dealer performs SI diagnostics for the customer’s concern.

• If diagnostics point to the coolant control valve: perform Engine Coolant Flow Control Valve Replacement under this Special Coverage at no charge.

• If diagnostics do not lead to the valve, only diagnostic time may be claimed under this action—no parts replaced under the coverage.

Parts listed in the bulletin (LM2):

• Engine Coolant Flow Control Valve: P/N 40009644

• Oil Level Indicator Seal: P/N 12670252

• Engine Coolant: 12346290 (US) / 10953464 (CA)

Parts availability note: Initial supply is limited. Dealers are advised not to stock for the shelf; expect orders to be placed as needed for individual vehicles.

How to Confirm Coverage on Your Vehicle

Ask your dealer to check your VIN in IVH → Applicable Warranties for N252508341. If your vehicle is listed and diagnostics confirm the valve, the repair is covered within the stated time/mileage window.

Reimbursement If You Already Paid

Owners who previously paid for a repair correcting this condition are eligible to request reimbursement in line with the bulletin’s procedures. The owner letter includes the required documentation and timing; work with your dealer for faster processing or follow the mail-in instructions. GM notes that reimbursement rights are personal to the customer and not assignable to third parties.

Why These Years and Lines?

The coverage spans 2021–2022 for LM2 1500 pickups and 2021–2023 for the full-size SUVs (including Escalade). GM does not specify the underlying reason in the bulletin. If you’ve had a coolant control valve replaced on an LM2 outside these listed years, share your build date, mileage, DTCs, and part number from the repair order so we can update this article.

Prior Evidence of Internal Breakage

We’ve previously shown internal breakage of these coolant control valves on our channel—real teardown footage. If you want to see what failure looks like, refer to our earlier video for context.

What I Would Do (Owner Checklist)

1. Scan for codes if you see a MIL or your fans run after key-off.

2. Call your dealer and request an IVH check for Special Coverage N252508341 on your VIN.

3. Let them diagnose it. If the valve is the cause, the replacement is covered within the 15-year/150k window.

4. Expect an order. With limited initial supply, parts are typically ordered per-vehicle rather than pulled from shelf stock.

5. If you already paid, start the reimbursement process and keep copies of your RO and proof of payment.

Related Reading

• LZ0 Special Coverage for coolant control valve: N252508340 (2023 Silverado/Sierra LZ0) — see our separate article for details.

Source / Attribution: GM Special Coverage Bulletin N252508341 – LM2 Coolant Control Valve Replacement, Release Date: September 2025, Rev 00.

If you have documentation showing a part supersession for P/N 40009644 or coverage applied to additional build dates, please send your repair order details so we can update this page.