P26BB on Chevrolet: How to Diagnose & Fix
Engine Coolant Bypass Valve "C" Range/Performance
1 Chevrolet model · 1 documented issue
P26BB on Chevrolet by model: symptoms, diagnosis and fix
Silverado 1500 trucks with the 3.0L LM2 Duramax inline-6 turbodiesel are prone to failure of the electronically actuated engine coolant control valve. Failure illuminates the check-engine light, can leave cooling fans running after the key is off (draining the battery), and in some cases causes the engine to run hotter than normal. A frequent root cause is corrosion/terminal damage in the coolant flow control valve actuator harness connector. GM announced Special Coverage N252508341 (September 2025) extending warranty to 15 years / 150,000 miles from in-service date for the affected valve on 2021-2022 Silverado 1500 (and 2021-2023 Tahoe/Suburban and GMC/Cadillac siblings). Owners have reported multi-month back-orders on the replacement valve (part 40009644).
Common Symptoms
- Check engine light
- Cooling fans run after engine is shut off
- Engine running hotter than normal
- Battery drain
How to Fix
Scan for codes (P1098 / P26BB are commonly reported); confirm the coolant control valve or its harness connector is at fault. Under Special Coverage N252508341 the dealer replaces the coolant control valve (part 40009644) at no charge within 15 years/150k miles. Inspect/repair the actuator harness connector for terminal corrosion. Reimbursement is available for owners who previously paid for the repair.
Sources for this issue (1)
P26BB code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P26BB mean on a Chevrolet?
P26BB stands for "Engine Coolant Bypass Valve "C" Range/Performance." A generic OBD-II code indicating engine coolant bypass valve C is electrically operating but its performance (actual coolant flow/temperature response versus expected) is out of range. On some vehicles this can appear transiently during the valve break-in period and self-clear after further actuations. On Chevrolet it is documented across 1 model: Silverado 1500.
What are the most common causes of P26BB?
The most common causes of P26BB are: Coolant bypass valve C sticking or slow to respond, Debris/contamination affecting valve travel, Valve break-in variation (low mileage), Coolant flow restriction, Valve wear or internal fault, Faulty ECM (rare). The specific cause varies by vehicle.
How much does it cost to fix P26BB on a Chevrolet?
Repair costs vary widely with the root cause and Chevrolet model; each issue on this page carries its own estimate where one is published.
Looking for P26BB on a different make?
View P26BB across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.