P0266 on GMC
Cylinder 2 Contribution/Balance Fault
P0266 on GMC vehicles indicates cylinder 2 contribution/balance fault. Au7o has documented this code across 1 GMC model — most commonly on Sierra 3500HD. P0266 is a generic powertrain code indicating the engine computer detected that cylinder 2 is not contributing its expected share of power, meaning its output is unbalanced compared to the other cylinders. The PCM monitors crankshaft acceleration and fuel/injector behavior per cylinder, and an imbalance here often signals a misfire, fuel-delivery, or mechanical problem specific to cylinder 2. Left unaddressed, this can cause rough running, poor performance, and possible catalytic converter damage. Typical repair costs on GMC range from $600 to $5,000, depending on the specific model and root cause.
Common Causes of P0266
- •Faulty or clogged fuel injector on cylinder 2
- •Injector wiring or connector fault
- •Ignition fault (coil, plug) causing a cylinder-2 misfire
- •Low compression / mechanical issue (valve, ring) on cylinder 2
- •Vacuum or intake leak affecting that cylinder
- •Contaminated or restricted fuel supply
- •PCM driver circuit fault for that injector
P0266 on GMC by Model
GMC Sierra 3500HD(1 issue)
- Diesel Injector Failure Causing White Smoke and Rough Running2015-2024
The Bosch piezoelectric fuel injectors on the Duramax L5P and LML engines can fail due to contaminated fuel, high-mileage wear, or internal electrical faults. A failed injector causes white smoke on startup, rough idle, misfires on the affected cylinder, and fuel dilution of the engine oil. The high fuel rail pressures (up to 36,000 PSI on the L5P) stress the injectors over time. Contaminated fuel from bulk diesel stations accelerates injector wear.
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View P0266 across all makes →Frequently Asked Questions
What does P0266 mean on GMC?▼
P0266 stands for "Cylinder 2 Contribution/Balance Fault." P0266 is a generic powertrain code indicating the engine computer detected that cylinder 2 is not contributing its expected share of power, meaning its output is unbalanced compared to the other cylinders. The PCM monitors crankshaft acceleration and fuel/injector behavior per cylinder, and an imbalance here often signals a misfire, fuel-delivery, or mechanical problem specific to cylinder 2. Left unaddressed, this can cause rough running, poor performance, and possible catalytic converter damage. On GMC specifically, this code is documented across 1 model.
What causes P0266 on GMC vehicles?▼
Common causes on GMC: Faulty or clogged fuel injector on cylinder 2, Injector wiring or connector fault, Ignition fault (coil, plug) causing a cylinder-2 misfire, Low compression / mechanical issue (valve, ring) on cylinder 2, Vacuum or intake leak affecting that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0266 on a GMC?▼
Repair costs on GMC range from $600 to $5,000, depending on the specific model and root cause.
Which GMC models have P0266 documented?▼
Au7o has documented P0266 on 1 GMC model: Sierra 3500HD.