P0272 Cylinder 4 Contribution/Balance Fault: Causes, Diagnosis and Fixes
P0272 is the generic OBD-II code for “Cylinder 4 Contribution/Balance Fault”. Unlike the circuit codes, this is a performance code: the ECU's smoothness monitoring has measured crankshaft acceleration cylinder by cylinder and found cylinder 4 contributing too little — or occasionally too much — torque compared with its neighbours. The injector's electrical circuit is fine; what the ECU is telling you is that the combustion event on cylinder 4 is wrong. The classic causes are a worn injector whose delivery has drifted, a replacement injector fitted without its calibration code being programmed, or a mechanical problem in the cylinder itself.
Technical Background
Common-rail ECUs continuously correct each injector's delivery to smooth the engine (smoothness or cylinder-balance correction). P0272 logs when cylinder 4 needs more correction than the strategy allows — the ECU has run out of adjustment authority. Reading the correction values for all cylinders in live data is therefore the single most informative first check: they show exactly how far each cylinder has drifted and in which direction.
Missed injector coding is a documented and common trigger for this code family. Coded injector designs (Bosch IMA, Delphi C2i/C3i, Denso ID codes and similar) carry individual calibration values; fitting a replacement without programming its code leaves the ECU correcting for an injector that is no longer there. On coded Denso and Bosch families we cover, an uncoded replacement will typically set contribution/balance faults — P0263, P0266, P0269 or P0272 depending on the cylinder — within a short distance of fitting.
Vehicles Commonly Affected
- Any common-rail diesel with cylinder-balance monitoring — the strategy is standard across modern engines.
- Sibling codes: P0263 (cylinder 1), P0266 (cylinder 2), P0269 (cylinder 3) — the same fault logic applied per cylinder.
Symptoms
- Uneven idle or a rhythmic misfire feel, often worse cold.
- A single-cylinder knock that fades as the engine warms — a classic worn-injector presentation.
- Reduced power and increased consumption.
- Large correction values on cylinder 4 in live data, long before the code finally sets.
Causes
- Worn injector on cylinder 4 — delivery drifted beyond the ECU's correction authority through nozzle or valve-seat wear.
- Replacement injector fitted without its calibration code programmed, or with the wrong code.
- Low compression on cylinder 4 — the mechanical rival to the injector explanation.
- Valve clearance or camshaft problems affecting that cylinder's breathing.
- Injector seating faults — blow-by past the sealing washer disturbing combustion.
Diagnosis
- 1Read the smoothness/balance correction values for all cylinders in live data — the pattern and direction of cylinder 4's drift frames everything that follows.
- 2Check the vehicle's history: if any injector was recently replaced, verify the stored calibration codes against the codes printed on the physical injectors, cylinder by cylinder.
- 3Run a comparative leak-back test across all injectors — internal wear on the cylinder 4 injector shows up as an outlier. The exact procedure and specification varies by manufacturer and engine.
- 4Rule out the mechanical rivals: compression test cylinder 4, and check valve clearances where the engine uses adjustable clearances.
- 5Inspect the injector seat area for blow-by evidence — carbon tracking around the injector body.
- 6Bench-test the cylinder 4 injector for delivery accuracy across its map — the definitive proof of delivery drift the vehicle cannot provide.
Common Mistakes
- Treating P0272 as an electrical fault and testing the circuit — this is a performance code; the circuit is usually fine.
- Overlooking a recent injector replacement and the coding mismatch it introduced — the quickest fix on the list when present.
- Condemning the injector without ruling out compression — the mechanical causes mimic injector drift exactly.
- Copying the old injector's code onto a replacement — every injector's calibration code is unique to that unit.
When It's Not the Injectors
- Low compression on cylinder 4 — always worth ruling out before injector work.
- Valve train faults affecting one cylinder.
- Seating/washer blow-by — an installation fault around the injector rather than the injector itself.
When Replacement Is Required
When bench testing confirms delivery drift beyond specification, the wear cannot be reversed by cleaning — remanufacture (new nozzle and valve set, recalibration, fresh calibration code) or a remanufactured exchange unit is the repair. If the cause was a coding mismatch, programming the correct code is the entire fix — no parts required.
Repair
Compatible Engines
Compatible Injectors
Frequently Asked Questions
What is the difference between P0272 and P0204?
P0204 is electrical — the ECU cannot drive the cylinder 4 injector circuit. P0272 is performance — the circuit works, but cylinder 4's combustion contribution is wrong. They lead to completely different diagnostic sequences.
An injector was just replaced and now I have P0272 — coincidence?
Probably not. Fitting a coded injector without programming its calibration code — or copying the old unit's code — is a documented trigger for contribution/balance faults shortly after fitting. Verify the stored codes against the injectors first; it may be a programming fix, not a parts problem.
Can injector cleaner clear a P0272?
Only in the minority of cases where light deposits are disturbing the spray. Genuine delivery drift comes from nozzle and valve-seat wear, which no additive reverses — that is proven, and fixed, on a test bench.