OBD-II Diagnostic Trouble Code
P0266 — Cylinder 2 Contribution/Balance Fault
P0266 means the ECM measured an abnormal power contribution from cylinder 2 using crankshaft speed analysis. The injector circuit is electrically OK, but the cylinder is producing more or less power than the others. This points to injector performance, compression or valvetrain problems.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Cylinder 2 Contribution/Balance Fault
Code
P0266
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
What this means for truckers
Service within a few days on a Cummins X15, Detroit DD15, PACCAR MX-13. Performance is likely degraded. Continuing to drive without service risks additional component damage.
Before you replace parts — try this first
P0266 on the Fuel system is most often worn, sticking or leaking cylinder 2 injector — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Rough idle, vibration, a mild miss, reduced power and possible smoke, usually most noticeable at idle and light load. Fuel economy may decline.
Common causes
- CommonWorn, sticking or leaking cylinder 2 injector ($400–$2500)
- OccasionalLow compression in cylinder 2 ($800–$6000)
- OccasionalValve or injector lash out of adjustment, worn rocker or cam lobe ($300–$3000)
- OccasionalWrong injector trim code programmed ($100–$250)
How to fix
Perform a cylinder cutout or balance test to confirm cylinder 2 is the problem.
When to use: First step.
Verify injector trim codes in the ECM.
When to use: After any injector or ECM replacement.
Check compression and valve lash on cylinder 2.
When to use: When the injector is suspected but not confirmed.
Replace the cylinder 2 injector.
When to use: When mechanical checks pass and the cylinder remains weak.
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0200 — Injector Circuit Malfunction
- → P0201 — Injector Circuit Malfunction - Cylinder 1
- → P0202 — Injector Circuit Malfunction - Cylinder 2
- → P0203 — Injector Circuit Malfunction - Cylinder 3
- → P0204 — Injector Circuit Malfunction - Cylinder 4
Frequently Asked Questions
Can I drive with code P0266?
P0266 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0266 on a commercial truck?
Total repair cost ranges $100–$6000 depending on the root cause. The cheapest fix is usually the first one listed below — Worn, sticking or leaking cylinder 2 injector — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0266 fail a DOT inspection?
P0266 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0266 and related codes?
P0266 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0266 is set without the companions, the issue is more isolated.
How do I prevent P0266 from coming back after a repair?
For P0266 (Cylinder 2 Contribution/Balance Fault), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.