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Severity: Moderate Code type: Generic (all makes)

P0266 Code: Cylinder 2 Contribution/Balance

The engine computer can't even out cylinder 2 with fuel corrections; its balance rate is past the limit.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Cylinder 2 Contribution/Balance
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$60–$7,500
DIY difficulty
Hard

Diesel engine computers balance the cylinders at idle by watching crankshaft speed and nudging each injector's fuel quantity up or down. P0266 says the correction for cylinder 2 has run out of room. On a Duramax that correction is the balance rate, shown in cubic millimeters per stroke on a scan tool: a big positive number means the computer is adding fuel to prop up a weak cylinder 2, while a big negative number means it's taking fuel away because injector 2 is delivering more than asked, typically through internal leakage. Cylinder 2 on the Duramax is the front cylinder on the passenger side; on the Navistar-built Power Stroke it's the driver-side front, and on Cummins and inline four-cylinders it's the second from the front. Watching the balance rates before the light even comes on is the best early warning of a failing injector.

Can I keep driving? Drivable in the short term, but a leaking injector can put fuel in the oil and wash down the cylinder, so check the dipstick for a rising level and a diesel smell. Don't tow heavy loads until the balance rates have been read.

How to read P0266

How to read P0266P10223664
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 66 Specific fault

Symptoms

  • Idle shake that you can feel in the steering wheel or seat
  • White smoke or raw fuel smell at idle, especially cold
  • Engine oil level creeping up between changes
  • Fuel economy dropping without an obvious reason
  • Light knock that follows cylinder 2 in a cut-out test

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Injector 2 leaking internally and over-fueling (large negative balance rate) 36%
  2. Injector 2 nozzle worn or partly plugged, under-fueling (large positive balance rate) 17%
  3. Low compression in cylinder 2 14%
  4. Air in the fuel or a restricted filter making all balance rates swing 12%
  5. Injector 2 not seated properly after service, or a damaged sealing washer 10%
  6. High resistance in the injector 2 connector or harness 6%
  7. New injector installed without its trim code programmed 5%

Diagnosis step by step

Diagnostic flow: P02661Record balance rates correctly2Read the pattern, not just cylinder23Look for fuel in the oil4Have a return rate test done5Check compression on cylinder 26Verify after replacement

  1. Record balance rates correctly

    Fully warm engine, idle, A/C and other loads off, transmission in park. Watch the balance rates for a minute and note the typical value for each cylinder, not a single snapshot. Many Duramax technicians treat roughly ±4 mm³ as the line worth acting on.

    Tools: OBD-II scanner

  2. Read the pattern, not just cylinder 2

    One cylinder far out while the rest sit near zero points to that cylinder. All cylinders jumping around point to fuel supply: check for air entering at the filter head, a dirty filter or low lift pressure before blaming injectors.

    Tools: OBD-II scanner, Fuel pressure gauge

  3. Look for fuel in the oil

    Compare the oil level with the last change and smell the dipstick. A rising level with a diesel smell supports an internally leaking injector, the classic failure on early Duramax engines.

    Tools: Flashlight

  4. Have a return rate test done

    A shop can measure the return flow from each injector with a test kit. Injector 2 returning clearly more than its neighbors confirms internal leakage; normal return with a positive balance rate points to a plugged nozzle or compression.

    Tools: OBD-II scanner

  5. Check compression on cylinder 2

    Before buying an injector, run a relative compression test or measure with a diesel adapter. A cylinder 2 well below the others, more than about 10%, needs mechanical diagnosis.

    Tools: Compression tester

  6. Verify after replacement

    After an injector change, program its trim code if the engine uses one, bleed the fuel system and recheck balance rates warm. Cylinder 2 should now sit near the others without pushing a neighbor out of range.

    Tools: OBD-II scanner

Where the parts are

Ignition: coils and spark plugs per cylinder – P02661234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Fix air intrusion and replace fuel filter Yes $60–$250
Injector return rate test No $150–$350
Replace injector 2 No $900–$1,800
Replace all eight injectors No $4,000–$7,500
Oil change after fuel dilution Yes $90–$180

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Chevrolet

The early LB7 Duramax in Silverado HD trucks is well known for injectors that leak internally, showing up as large negative balance rates, white smoke and fuel in the oil. Later Duramax versions fail less often, but balance rates remain the first check.

GMC

Sierra HD trucks with the LB7 Duramax share the same injector leakage problem as the Silverado. Rising oil level together with a cylinder far out on balance rates is the typical pattern.

Emissions / smog test impact

Depends

Many heavier diesel pickups are exempt from, or tested differently in, state emissions programs. Where the truck gets an OBD check, a check engine light for P0266 fails it.

Frequently asked questions

What do the Duramax balance rates actually mean?

They're the fuel correction the computer applies to each cylinder at idle. Near zero is healthy; a large positive value means it's adding fuel to a weak cylinder, a large negative value means it's removing fuel from one that over-delivers.

Can air in the fuel set P0266?

It can make balance rates swing on every cylinder, and the one that swings furthest may set its code. Fix any air leaks and the filter first, then read the rates again before buying an injector.

Why is there fuel in my oil?

An injector that leaks internally can drain fuel into the crankcase instead of the return circuit. That dilutes the oil and is harmful to bearings, so change the oil after the repair.

Where is cylinder 2 on my truck?

On a Duramax it's the front cylinder on the passenger side. On a 6.0 or 6.4 Power Stroke it's the driver-side front, on the 6.7 Power Stroke it's second from the front on the passenger side, and on a Cummins it's second from the front.

Sources