OBD-II trouble code
P0275: Cylinder 5 Contribution/Balance Fault
Cylinder 5 is contributing less work than the rest. On the long inline diesels where this code lives, position five is at the hot end of the block — which gives it mechanical suspects the front cylinders do not have.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $4,000
- DIY difficulty
- Advanced DIY
Browse every code in P0200–P0299, or start from the full code library.
What does P0275 mean?
Only engines with five or more cylinders can set this code, and in practice the vehicles that set it most often are inline fives, inline sixes and heavy-duty diesels, where per-cylinder contribution — usually called balance rate — is a routine readout rather than a specialist measurement. That population shapes what is worth suspecting, because cylinder 5 on a long inline engine is not in a neutral place.
Coolant enters an inline block at the front and works its way rearward, picking up heat from each cylinder it passes. By the time it reaches the fifth and sixth positions it is already carrying the heat of everything ahead of it, so the rear of a long inline engine runs measurably hotter than the front. That is why the rear cylinders of inline sixes are the classic location for heat-related distress: cracked heads between the valve seats, burnt exhaust valves, and on wet-liner and cup-injector designs, erosion of the injector sleeve. A balance fault on a rear cylinder therefore carries a mechanical prior that the same fault on cylinder 1 does not, and it is worth taking that seriously before assuming the injector is simply tired.
The injector cup is worth naming specifically because it produces a distinctive and time-critical picture on heavy-duty diesels. The injector sits in a thin copper or steel sleeve that separates it from the coolant jacket. When that sleeve cracks or erodes — and it does so preferentially in the hot rear cylinders — coolant enters the cylinder. The result is a weak contribution from that cylinder, a coolant level that falls steadily with no external leak and no puddle on the ground, and sometimes white vapour at start-up. That is a completely different investigation from a worn injector, and it has a deadline: liquid in a cylinder that cannot compress is how a good engine becomes a bent connecting rod. If this code is accompanied by coolant loss you cannot account for, stop and pressure-test the cooling system before running the engine further.
Where the fault really is fuelling, a diesel gives you a very readable measurement. The module trims each cylinder's delivery slightly to smooth crankshaft speed, and the balance rate is the size of that trim. A healthy engine has every cylinder sitting close to zero and close to its neighbours. A cylinder needing a large positive correction is being fed extra fuel to keep up, which means it is producing less work than it should for the fuel it was getting. Record the whole set at idle and again at a raised steady speed rather than at one condition, because injectors that have worn tend to show worse at low delivery, and a fault that only appears at idle points somewhere different from one that grows with load.
There is a parts consequence unique to multi-cylinder diesels, and it catches people who fix the cylinder correctly and still end up with a code. Modern diesel injectors are manufactured with small flow variations and are supplied with calibration or trim codes that must be programmed into the module against the cylinder they are fitted to. Fit a new injector without entering its code and the module keeps applying the old injector's correction to a part that does not need it — which produces a fresh balance fault on the cylinder you have just repaired. On high-mileage engines there is also a fairness argument for sets: one new injector among five worn ones is the outlier in the other direction, and the balance monitor will notice.
On a V6 or V8, the useful refinement is to compare cylinder 5 against its own bank rather than against the whole engine. Bank-level problems — an intake gasket leaking on one side, one restricted catalytic converter, one exhaust leak upstream of a sensor — shift every cylinder on that bank together, and against a whole-engine average that can name a single cylinder that is no worse than its immediate neighbours. Grouping the readings by bank before interpreting them takes a moment and prevents a cylinder-level repair for a bank-level problem.
The reason to test rather than to buy is arithmetic. A compression and leak-down test on cylinder 5 costs a small fraction of a diesel injector, and on the engines that set this code the injector is the expensive part in the vehicle after the turbocharger. Ruling out compression first is not caution — it is the cheapest step available.
Common causes
- Worn diesel injector delivering late or atomising poorly, showing as a large positive balance rate on that cylinder
- Cracked or eroded injector cup or sleeve admitting coolant into the cylinder, a failure that concentrates in the hot rear cylinders of long inline engines
- Burnt exhaust valve or a cracked head at the rear of the block, where an inline engine runs hottest
- Low compression on cylinder 5 from worn rings or a valvetrain fault
- New injector fitted without its calibration or trim code programmed to the module, which recreates the fault on a repaired cylinder
- One worn injector left among a set of otherwise matched replacements, or the reverse
- Bank-level problem on a V engine shifting every cylinder on that side, so the whole-engine average names one
- Worn spark plug or failing ignition coil on cylinder 5 on gasoline applications
- Low fuel supply pressure or a restricted filter, which shows on the weakest cylinder before it shows generally
Symptoms
- Check engine light on
- Rough idle with an uneven combustion note, often audible as a knock on a diesel
- Reduced power and hesitation under load
- A balance rate readout in which cylinder 5 needs a large positive correction while its neighbours sit near zero
- Coolant level falling steadily with no external leak, which points at the injector cup rather than the injector
- White vapour at start-up on engines losing coolant into a cylinder
- Companion misfire codes such as P0305 or P0300
- Hard starting, extended cranking and black smoke on diesel applications
Diagnostic steps
- 1.Check the coolant level and pressure-test the cooling system if there is any unexplained loss. A cracked injector cup at a rear cylinder produces this code and can hydraulically damage the engine if it is driven further.
- 2.Read every stored code first. An injector circuit code on the same cylinder means the fault is electrical, and repairing it normally clears the balance fault.
- 3.Record balance rates for every cylinder at idle and again at a raised, steady engine speed. One condition is not enough — an injector that only misbehaves at low delivery tells a different story from one that worsens with load.
- 4.On a V engine, group the readings by bank before interpreting them. A bank-level fault shifts every cylinder on that side and can name a single cylinder that is no worse than its neighbours.
- 5.Confirm which physical cylinder the manufacturer calls number 5, since numbering on V6 and V8 engines varies and cylinder 5 is where the conventions diverge.
- 6.Compression- and leak-down-test cylinder 5 before ordering anything. On a diesel this test costs a small fraction of the injector and either clears the mechanical path or prevents a repair that could not have worked.
- 7.Pay particular attention to valve sealing and head condition at this position on a long inline engine, since the rear cylinders run hottest and are where heat-related failures concentrate.
- 8.On a gasoline engine, compare the cylinder 5 spark plug against the others and swap its coil to a neighbouring cylinder to rule ignition in or out quickly.
- 9.Check fuel supply pressure under load and inspect the filter, since a marginal supply presents as one weak cylinder before it presents as a general fault.
- 10.If an injector is replaced, program its calibration or trim code to the module. Skipping that step reproduces the balance fault on the cylinder you have just repaired.
Repair cost
$100 – $4,000
The engines that set this code carry the expensive version of every outcome. A spark plug or coil on a gasoline application is $100 to $350 installed and a gasoline injector $60 to $400 in parts. Diesel injectors are the defining cost at $400 to $900 each installed, and on a high-mileage engine a full set of five or six commonly reaches $2,000 to $3,500 — plus programming of each injector's calibration code, which is not optional. An injector cup or sleeve replacement is $600 to $2,000 depending on whether the head has to come off, and if coolant has already been in the cylinder the figure can go much higher. Mechanical repairs at a rear cylinder — a burnt valve or a cracked head on a long inline engine — start near $1,500. Diagnosis alone is $100 to $250.
Estimate your repair
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Open the Repair Cost Estimator with fuel injector replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.