I have contribution codes on several cylinders. Does the pattern tell me anything?

It tells you a great deal. Map the affected cylinders to banks. If they are all on one bank, look at what that bank shares — fuel rail pressure on that side, an intake plenum or runner gasket leak, or a bank-specific camshaft timing problem. If they are spread across both banks, the shared item is the whole fuel supply: pressure, a restricted filter, contaminated fuel, a failing pump, or a weak high-pressure pump on a direct-injection engine. Either way, testing the shared system is one step, while testing six cylinders individually is six.

Should I do a compression test before replacing the injector?

Yes. A worn ring pack or a burnt valve produces exactly the same weak-contribution reading as a tired injector, and a new injector cannot restore compression. On cylinder 6 this matters even more than on the front cylinders, because reaching a rear-bank injector often means removing the intake manifold — so a wrong guess costs the teardown as well as the part. A compression and leak-down test either clears the mechanical path or saves you the whole job.

What is the fastest way to confirm the injector?

Swap it. Once ignition and compression have checked out, move the cylinder 6 injector to another cylinder and put that cylinder's injector into position 6. Clear the codes and drive. If the balance fault follows the suspect injector to its new cylinder, you have proof without buying anything. If the fault stays on cylinder 6, the injector is not the problem and you have saved yourself a part.

Can I drive with P0278?

Short trips to a shop are generally fine, since the engine still runs. It should not be ignored, though. A cylinder burning its fuel incompletely sends unburned fuel into the exhaust, which can overheat the catalytic converter on that bank over time. If the check engine light begins flashing, stop driving and have the vehicle towed.

OBD-II trouble code

P0278: Cylinder 6 Contribution/Balance Fault

Cylinder 6 is producing less power than the other cylinders, measured through crankshaft speed. Fuel, ignition and compression all read the same here — and if other cylinders on the same bank are weak too, look at what they share.

Medium severityPowertrainFuel InjectorsDrivable short-term

Quick facts

System: Powertrain
Category: Fuel Injectors
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $100 – $3,500
DIY difficulty: Intermediate DIY

What does P0278 mean?

P0278 reports an outcome, not a wiring condition. The engine control module (ECM) reads crankshaft rotational speed at high resolution through the crankshaft position sensor. Every power stroke gives the crankshaft a brief acceleration whose size reflects how much work that cylinder produced, and the ECM compares all cylinders against each other. When cylinder 6 falls outside the allowed spread, P0278 sets.

Because the measurement is of a result, three unrelated systems can produce the same code. Fuel: a restricted, worn, or slow-opening injector delivers less than commanded. Ignition: on a gasoline engine, a worn plug or a coil breaking down under load leaves combustion incomplete. Compression: worn rings, a burnt or leaking valve, or a head gasket leak means the cylinder cannot turn combustion into pressure on the piston. From the crankshaft sensor's point of view they are indistinguishable, which is why the diagnostic value of this code lies entirely in the order you test things: plug and coil first because they are free and fast, compression and leak-down second because they are cheap and definitive, and the injector last because it is the expensive one. Fitting a new injector to a cylinder that has lost compression is the most common costly mistake on this family of codes.

P0278 has one distinguishing feature the earlier contribution codes do not: by the time you are on cylinder 6, the engine has at least two banks or a long shared fuel rail, and a pattern across cylinders becomes informative. Look at which other contribution codes are stored. If cylinder 6 is weak on its own, a single failed component on that cylinder is likely. If cylinders 4, 5 and 6 are all weak and they happen to be one bank, suspect something they share — a fuel rail pressure drop on that side, a leaking intake plenum gasket feeding that bank, a bank-specific camshaft or timing issue, or a fuel supply line restriction. If cylinders across both banks are weak, the shared item is the whole fuel supply: pressure, filter, contaminated fuel, a failing pump, or a weak high-pressure pump on a direct-injection engine. Testing cylinder by cylinder in those cases is slow and misleading; testing the shared system finds it in one step.

On diesel engines the analysis narrows to fuel and compression only, since there is no ignition system to rule out, and per-cylinder contribution or balance-rate readouts are a routine diagnostic rather than an exotic one. Diesel injectors degrade gradually — opening later and flowing less as they wear — which is exactly the slow decline a balance monitor catches long before a misfire code would.

Common causes

Restricted, dirty, or internally worn cylinder 6 fuel injector
Injector opening late or producing a poor spray pattern under load
Worn spark plug or failing ignition coil on cylinder 6 (gasoline engines)
Low compression on cylinder 6 from worn rings, a burnt valve, or a valvetrain fault
Head gasket leaking between cylinder 6 and a neighboring cylinder or into coolant
Intake plenum or runner gasket leak affecting one bank, which shows up first on its weakest cylinder
Low fuel pressure, a restricted fuel filter, or contaminated fuel
Weak high-pressure fuel pump on a direct-injection engine
High-resistance wiring or a corroded connector at the cylinder 6 injector

Symptoms

Check engine light on
Rough idle and a shake most noticeable at low RPM
Reduced power and hesitation under load
Companion misfire codes such as P0306 or P0300
Poor fuel economy
Hard starting or extended cranking, particularly on diesels
Excessive or black exhaust smoke on diesel applications

Diagnostic steps

1.Read every stored code first. P0206, P0276, or P0277 present with P0278 means the injector circuit is electrically faulty — repair that and the balance fault normally resolves with it.
2.Note which OTHER contribution codes are stored and map them to banks. A whole-bank pattern points at something shared; a single-cylinder pattern points at a single component.
3.Confirm which physical cylinder your engine calls number 6. On transverse V6s it is usually on the rear bank; V8 numbering varies by manufacturer.
4.Run the scan tool's cylinder balance, injector contribution, or diesel balance-rate test and record how far cylinder 6 sits from the others. A large, repeatable deviation is meaningful; a small wandering one often is not.
5.On a gasoline engine, remove and compare the cylinder 6 spark plug against the others. Heavy wear, fouling, or oil on the electrode explains the weak contribution by itself.
6.Swap the cylinder 6 ignition coil with a neighboring cylinder, clear codes, and drive. If the fault follows the coil, stop there.
7.Compression- and leak-down-test cylinder 6 before buying fuel components. This is the step that separates a worn engine from a weak injector, and skipping it is the most common cause of a repeat repair.
8.Check fuel rail pressure under load — and on a V engine with separate rails or a crossover line, check pressure on the affected bank specifically. Inspect the fuel filter at the same time.
9.Smoke-test the intake for a plenum or runner gasket leak on that bank, which can starve one bank of the mixture the ECM expects.
10.If fuel supply, ignition, and compression all check out, swap the cylinder 6 injector with one from a healthy cylinder and see whether the fault follows the injector.

Repair cost

$100 – $3,500

A spark plug or ignition coil on the weak cylinder is typically $100-$350 installed. A gasoline fuel injector runs $60-$400 in parts plus 0.5-3 hours labor, with a rear-bank cylinder 6 at the top of that range and often including intake gaskets. Diesel injectors commonly reach $400-$900 each installed, and a full set on a high-mileage engine can run $2,000-$3,500. Fuel filter or fuel pressure repairs generally land at $150-$800, and a high-pressure fuel pump on a direct-injection engine is $600-$1,600. Mechanical causes — rings, a burnt valve, or a head gasket — start near $1,200 and can exceed $3,000. Diagnosis alone is usually $100-$200, since this code requires a sequence of tests rather than one measurement.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.