P0278

Cylinder 6 Contribution/Balance Fault

P0278 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 6 Contribution/Balance Fault. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0278
Group
Powertrain
System
Fuel/Inj
Severity
Warning (MIL on, possible limp mode)
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What P0278 means

P0278 — Cylinder 6 Contribution/Balance Fault — means the PCM has determined that cylinder 6 is producing less power than the other cylinders during its power stroke. The PCM tracks each cylinder's contribution by measuring the crankshaft acceleration that occurs immediately after each combustion event; when cylinder 6 consistently shows less acceleration than its neighbours, the balance threshold is exceeded and P0278 is stored. The MIL illuminates and a freeze-frame is captured.

The code applies to any OBD-II vehicle with six or more cylinders — V6, inline-6, V8, V10, and V12 layouts all have a cylinder 6. It is common on GM 6.6 L Duramax diesel trucks, Ford 6.0/6.7 Power Stroke diesels, Mercedes-Benz V6 CDI engines, and petrol V6/V8 platforms from a wide range of manufacturers. On diesel vehicles the PCM additionally tracks injector quantity-balance rates; a cylinder 6 rate outside the allowed window (often ±4 mg/stroke) will set P0278 before a misfire is felt. On petrol engines the code is typically accompanied by a companion P0306 misfire code.

The most common cause is a fuel-delivery problem specific to cylinder 6: a partially clogged, leaking, or electrically compromised injector. Mechanical causes — low compression from worn rings, a burnt valve, or a leaking head gasket on cylinder 6 — produce identical symptoms and must be ruled out via compression testing before injector replacement. Leaving this fault unaddressed risks catalyst damage on petrol engines and potential injector failure escalation on diesel platforms.

Common causes

Most-frequently reported root causes when P0278 is logged.

  • 1
    Clogged or mechanically degraded fuel injector on cylinder 6 delivering insufficient or incorrect fuel quantity.
  • 2
    Failed injector solenoid winding (open or high resistance) causing partial or no actuation.
  • 3
    Corroded or loose injector electrical connector on cylinder 6.
  • 4
    Low fuel rail pressure insufficient to open cylinder 6 injector fully.
  • 5
    Low compression on cylinder 6 from worn piston rings, a burnt valve, or a leaking head gasket.
  • 6
    Faulty camshaft or crankshaft position sensor providing inaccurate timing data to the PCM.
  • 7
    Contaminated or water-diluted fuel reducing combustion energy on the affected cylinder.
  • 8
    PCM fault corrupting injector-duration calibration for cylinder 6 (rare).

Symptoms drivers notice

Malfunction Indicator Lamp (MIL) illuminated.
Rough idle with perceptible engine vibration or shake.
Misfiring, stumbling, or hesitation under load.
Noticeable reduction in power and acceleration.
Increased fuel consumption.
Excessive black or white exhaust smoke indicating combustion irregularity.

How to diagnose P0278

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze-frame data with a scan tool; companion codes P0306 (misfire) and P0261/P0262 (injector circuit low/high) help narrow the root cause.
  2. 2
    On diesel vehicles, read live injector balance-rate or quantity-correction data for all cylinders; a cylinder 6 deviation outside ±4 mg/stroke confirms a fuelling problem.
  3. 3
    Use a bidirectional scan tool to perform a cylinder contribution or cut-out test and confirm cylinder 6 is the underperforming unit.
  4. 4
    Inspect the cylinder 6 injector connector and harness for corrosion, pushed-out pins, or damage; measure injector coil resistance against specification.
  5. 5
    Verify fuel rail pressure at idle and at high load; insufficient pressure affects balance across cylinders, with the most marginal cylinder (often 6) failing first.
  6. 6
    Perform a compression test on cylinder 6; a reading more than 10 % below adjacent cylinders indicates a mechanical cause such as ring or valve wear.
  7. 7
    Clean or replace the cylinder 6 injector after ruling out mechanical and electrical root causes; recheck balance rates after repair to confirm resolution.

Related powertrain codes

Frequently asked questions

Is P0278 only a diesel engine code?

No. P0278 is a generic OBD-II code that applies to petrol and diesel engines with six or more cylinders. Diesel platforms provide more granular balance-rate data, making the code easier to pinpoint, but petrol V6 and V8 engines can also set P0278 when cylinder 6 misfires consistently.

Can I drive with P0278 active?

Short trips at moderate load are generally tolerable, but extended highway driving or heavy towing should be avoided. The misfiring cylinder can overheat the catalytic converter on petrol engines, and a worsening injector fault on diesel engines can lead to hydro-lock or bearing damage.

P0278 cleared itself — is the problem gone?

Not necessarily. Intermittent injector faults caused by heat-sensitive wiring or a partially clogged injector can clear when conditions change. If the code returns after a few drive cycles, the underlying fault is still present and should be diagnosed before further damage occurs.

Should I replace the injector or clean it first?

Start by confirming the injector is the actual cause via balance-rate data and coil resistance testing. If resistance is within spec and the connector is sound, professional ultrasonic cleaning is worth attempting. If the injector delivers incorrect flow after cleaning, or the coil is open, replacement is required.

Disabling P0278 in software

RaceTune can permanently disable P0278 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P0278 disable in our catalogue

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