LZ0 3.0 Duramax: GM Issues Special Coverage for Coolant Control Valve (N252508340)

Greg Nelson
Sep 16
4 min read

Release: September 2025 • Bulletin: N252508340 • Applies to: 2023 Chevrolet Silverado 1500 / 2023 GMC Sierra 1500 with LZ0 3.0L Duramax

At a Glance

What happened: GM announced a Special Coverage for potential engine coolant control valve failures.
Coverage window: 15 years or 150,000 miles from original in-service date (whichever comes first), regardless of ownership.
Symptoms: MIL/Check Engine Light with related DTCs (commonly P1098), cooling fans running after key-off, and in some cases coolant leak at the valve.
The fix: If diagnostics point to the valve, dealers replace it at no charge under this Special Coverage.
Models affected: 2023 Silverado 1500 / Sierra 1500 LZ0 only (not listed for LM2 or 2024–2025 LZ0).
Reimbursement: If you already paid for this repair, GM offers reimbursement; deadline: October 31, 2026.

What “Special Coverage” Means (Plain English)

This is not a recall and not a blanket part swap. Special Coverage is similar to an extended warranty for a specific part when a specific condition occurs. GM will cover the repair only if diagnostics confirm the coolant control valve is the cause. No charge to the customer inside the 15-year/150k-mile window.

Who’s Covered

Model year: 2023 only
Vehicles: Chevrolet Silverado 1500 / GMC Sierra 1500
Engine: LZ0 3.0L Duramax

If you drive a 2020–2022 LM2, or a 2024–2025 LZ0, this bulletin does not list your truck.

Symptoms & Common Codes

Owners and techs should look for:

MIL/Check Engine Light with a valve-related DTC—commonly P1098
Engine cooling fans that keep running after shutdown
Visible coolant leak from the Engine Coolant Flow Control Valve assembly

If you see these signs, it’s time for a proper diagnosis.

The Fix (Dealer Procedure Summary)

Dealer follows SI diagnostics.
If diagnostics lead to the valve, dealer performs Engine Coolant Flow Control Valve Replacement under the Special Coverage.
If diagnostics do not point to the valve, the bulletin allows diagnostic time only—no parts replaced under this coverage.

Parts listed in the bulletin:

Engine Coolant Flow Control Valve: P/N 40009452
Oil Level Indicator Seal: P/N 12670252
Engine Coolant: 12346290 (US) / 10953464 (CA)

Note: As of this writing, the valve’s P/N 40009452 has not changed in recent months to our knowledge. If you’ve seen a supersession on an RO, send it our way so we can update this article.

Parts availability: Initial supply is limited. Dealers are instructed to Customer Special Order (CSO); stocking is discouraged. Expect some wait time while orders are filled.

How to Confirm Coverage on Your Truck

Call your dealer and ask them to check your VIN in IVH → Applicable Warranties within GM’s Global Warranty Management system. If your truck is listed and diagnostics confirm the failure, the repair is covered.

Reimbursement If You Already Paid

If you previously paid to fix this condition, you can request reimbursement.

Deadline to submit: October 31, 2026 (or longer if state law allows).
How: Work through your dealer for faster processing or mail your completed reimbursement form and documents to:Reimbursement Department, PO Box 33170, Detroit, MI 48232-5170

Keep copies of your repair order, proof of payment, and any related documents. Per GM, reimbursement rights are personal to owners/lessees and not assignable to third parties.

Why 2023 Only?

That’s the big question. Running change? Supplier batch window? Calibration nuance? GM’s bulletin lists 2023 LZ0 only. If you have a 2024 or 2025 LZ0 and have already had a valve replaced under warranty, share your build date, mileage, DTCs, and the part number used on your RO so we can compare data points.

Prior Evidence of Internal Breakage

We’ve previously documented internal breakage of these coolant control valves on the channel. If you want to see what failure looks like inside the assembly, check out our earlier video where we tear one down on camera.

What I Would Do (Owner Checklist)

Scan for codes. If you see P1098 or related valve codes, or your fans run after key-off, or there’s coolant at the valve, call the dealer.
Ask for an IVH check. Have the service advisor confirm Special Coverage N252508340 under Applicable Warranties for your VIN.
Let them diagnose it. If diagnostics point to the valve, the replacement is covered inside the 15-year/150k-mile window.
Expect a parts order. With limited supply, most dealers will CSO the valve. Get on the list early.
Already paid? Start the reimbursement process now; don’t miss the 10/31/2026 deadline.

Final Thoughts

This Special Coverage is a meaningful safety net for 2023 LZ0 owners seeing MILs, post-shutdown fan operation, or coolant at the valve. It’s not a proactive replacement program, but if diagnostics confirm the issue, the repair is covered for a long time—15 years/150k miles is substantial.

If you’ve had a valve replaced on a 2024–2025 LZ0, or you have documentation of a new part number/supersession, send your RO details and build date so we can update this page and help the community see the full picture.

Source / Attribution: GM Special Coverage Bulletin N252508340 – LZ0 Coolant Control Valve Replacement, Release Date: September 2025, Rev 00.Owner letter and reimbursement details summarized from the same bulletin.

Editor’s note: We’ll update this article as we verify part number changes, add owner reports, and track parts availability.