OBD-II trouble code
P0272: Cylinder 4 Contribution/Balance Fault
Cylinder 4 was named as the weak one by a comparison against the other cylinders. On a four-cylinder engine that comparison has only three others to average against, which makes it easier to distort than most people assume.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $3,000
- DIY difficulty
- Intermediate DIY
Browse every code in P0200–P0299, or start from the full code library.
What does P0272 mean?
This code is the output of a comparison, not of a measurement, and understanding that distinction is what keeps the diagnosis honest. Nothing in the vehicle knows how much power cylinder 4 ought to make. What the module does is read crankshaft speed at high resolution, note the small acceleration each power stroke produces, and compare the cylinders against one another. Cylinder 4 was not found to be weak in any absolute sense. It was found to be further from the group than the calibration allows.
That has an immediate consequence on a four-cylinder engine, and it is a statistical one rather than a mechanical one. With only four cylinders, each one is being judged against an average of three — the smallest sample any balance monitor works with. Small samples are easy to distort. If two cylinders are weak, they drag the average down and the genuinely weak ones look closer to normal than they are. If one cylinder is unusually strong, a perfectly healthy cylinder 4 can be pushed outside the allowed spread and named. So the first move on a four-cylinder is not to test cylinder 4 — it is to read the raw contribution figures for all four cylinders and see the shape of the distribution before trusting which one the code picked. On a six or eight the named cylinder is a much safer bet than it is here.
There is a second reason not to take the name at face value, and it is the most useful thing on this page. The measurement is crankshaft acceleration, read through a toothed reluctor wheel on the crankshaft or flywheel. Anything that puts a repeating error at one angular position of that wheel produces a repeating error attributed to whichever cylinder happens to fire there. A damaged or corroded reluctor tooth, a flexplate that has cracked around the ring gear, a loose crankshaft sensor bracket, or a slightly eccentric wheel will all show up as the same cylinder being weak, revolution after revolution, forever. The signature is distinctive once you know to look for it: the cylinder never gets better, never gets worse, tests perfect on compression, and the fault does not move when the injector is swapped. If you have reached that point, stop looking at cylinder 4 and go and inspect the reluctor and the sensor, because there is nothing wrong with the cylinder at all.
When the fault is real, three unrelated systems can produce it because the module is measuring an outcome rather than a cause. A worn or restricted injector delivers less fuel than commanded. A tired plug or a coil breaking down under load leaves combustion incomplete. Worn rings, a burnt valve or a head gasket leak means the cylinder cannot convert combustion into pressure on the piston. From the crankshaft's point of view these are indistinguishable, which is why the compression and leak-down test earns its place before any part is bought — fitting a new injector to a cylinder that has lost compression is the classic expensive mistake on this family of codes.
The intake side deserves a specific look on an inline four, because cylinder 4 sits at the end of the manifold. End runners are where uneven distribution shows up first. A manifold or throttle-body gasket leak at the end of the plenum admits unmetered air that reaches the end cylinder preferentially, and on engines that feed exhaust gas recirculation into one end of the plenum, the end cylinders can receive a noticeably different proportion of it than the middle ones. Both produce a genuine, repeatable weakness on one end cylinder with nothing wrong with its injector, its plug or its compression. Smoke-testing the intake is a quick check that is easy to skip and occasionally ends the whole investigation.
The consolation, as with everything on an inline four, is access. The plugs, coils and injectors are all on top of the head, so the definitive test — move cylinder 4's injector to another position and see whether the fault follows it — costs an hour and no parts. On this engine layout the swap test is not a last resort. It is one of the first things worth doing.
Common causes
- Restricted, dirty or internally worn cylinder 4 fuel injector
- Worn spark plug or an ignition coil breaking down under load on cylinder 4
- Low compression on cylinder 4 from worn rings, a burnt valve or a valvetrain fault
- Damaged reluctor tooth, cracked flexplate or a loose crankshaft sensor bracket, which attributes a repeating measurement error to whichever cylinder fires at that angle
- Intake manifold or throttle body gasket leak at the end of the plenum, which feeds unmetered air preferentially to the end cylinder
- Uneven exhaust gas recirculation distribution reaching the end runner differently from the middle ones
- Two weak cylinders skewing the average so the comparison names the wrong one
- Head gasket leaking between cylinder 4 and its neighbour or into the coolant
- High-resistance wiring or a corroded connector at the cylinder 4 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 P0304 or P0300
- A contribution or balance readout in which cylinder 4 sits consistently apart from the other three
- Poor fuel economy
- Hard starting or extended cranking
- A weakness that never varies at all across conditions, which points at the measurement rather than the cylinder
Diagnostic steps
- 1.Read the contribution figures for all four cylinders, not just cylinder 4. On a four-cylinder engine each cylinder is judged against only three others, so two weak cylinders or one unusually strong one can name the wrong cylinder.
- 2.Read every stored code first. An injector circuit code on the same cylinder means the fault is electrical — repair that and the balance fault normally clears with it.
- 3.Note whether the deviation is large and repeatable or small and wandering. A wandering figure within a narrow band is usually the monitor's noise floor rather than a fault.
- 4.Ask whether the weakness is absolutely constant. A deviation that never changes with load, temperature or fuel is the signature of a measurement error rather than a combustion problem.
- 5.Inspect the crankshaft reluctor and the crankshaft position sensor mounting if the fault never moves and the cylinder tests healthy. A damaged tooth or a cracked flexplate produces a permanent, unmoving weak-cylinder report.
- 6.Compare the cylinder 4 spark plug against the other three. Heavy wear, fouling or oil on the electrode explains the weak contribution by itself.
- 7.Swap the cylinder 4 coil with a neighbouring cylinder, clear codes and drive. If the fault follows the coil, stop there.
- 8.Compression- and leak-down-test cylinder 4 before buying any fuel component, since a new injector cannot restore compression.
- 9.Smoke-test the intake, paying attention to the end of the plenum and the manifold gasket nearest cylinder 4, where a leak reaches the end runner preferentially.
- 10.Use the access an inline four gives you and swap the cylinder 4 injector with a neighbour. If the fault follows the part you have your answer without spending anything.
Repair cost
$100 – $3,000
Access keeps most of the fuel and ignition outcomes cheap on this engine layout. A spark plug or ignition coil is $100 to $350 installed, and a four-cylinder injector is $60 to $400 in parts with only 0.5 to 1.5 hours of labour because it sits on top of the head. An intake or throttle body gasket leak found by smoke test is $150 to $500. The outliers are at both ends: a crankshaft reluctor, flexplate or sensor problem masquerading as a weak cylinder can be anything from $150 for a sensor to $900 or more if the flexplate has to come out, and genuine mechanical causes — rings, a burnt valve or a head gasket — start near $1,200 and can exceed $3,000. Diagnosis alone is $100 to $200, because this code needs 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.