P0263 on GMC: How to Diagnose & Fix
Cylinder 1 Contribution/Balance
1 GMC model · 1 documented issue · 1 critical · $600-$5,000 repair
P0263 on GMC by model: symptoms, diagnosis and fix
The fuel injectors on the Duramax LML (Bosch piezoelectric) and L5P (Denso solenoid) 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 (about 29,000 PSI on the L5P) stress the injectors over time. Contaminated fuel from bulk diesel stations accelerates injector wear.
Common Symptoms
- White or gray smoke on cold start
- Rough idle or misfire on one or more cylinders
- Fuel smell in engine oil (fuel dilution)
- Check engine light with injector circuit codes
- Reduced power and poor fuel economy
- Hard starting in cold weather
How to Fix
Diagnose the failed injector with a relative compression test and injector balance rate scan using a Tech 2 or equivalent scan tool. Replace the failed injector(s) — OEM injectors are $300-$500 each, and labor is 2-4 hours per injector ($300-$600). Always replace the injector hold-down clamp and fuel return line seals. If one injector fails at high mileage, consider replacing all 8 as the others are likely near end of life. Use a quality fuel additive like Stanadyne or Hot Shot Secret to protect remaining injectors.
Sources for this issue (2)
P0263 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 P0263 mean on a GMC?
P0263 stands for "Cylinder 1 Contribution/Balance." This code means the engine computer has detected a contribution or balance problem on cylinder 1, indicating that this cylinder is producing more or less power than the others. The computer monitors tiny speed changes from each cylinder's firing event and flags one that is contributing unevenly. It points to a fueling, compression, or mechanical imbalance specific to cylinder 1 (and, on some diesels, a related fuel injector circuit). You may notice rough idle, a misfire feel, or reduced power. On GMC it is documented across 1 model: Sierra 3500HD.
What are the most common causes of P0263?
The most common causes of P0263 are: Faulty fuel injector on cylinder 1, Clogged or leaking cylinder 1 injector, Low compression in cylinder 1 (valves, rings, head gasket), Worn or fouled spark plug / coil on cylinder 1 (gas engines), Injector wiring or connector fault on cylinder 1, Vacuum or intake leak affecting that cylinder, Carbon buildup or sticking valve on cylinder 1. The specific cause varies by vehicle.
How much does it cost to fix P0263 on a GMC?
Published repair estimates on GMC range from $600 to $5,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0263 on a different make?
View P0263 across all makes →Join 700+ subscribers following Au7o for vehicle insights and updates.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.