P0278 Cylinder 6 Contribution/Balance Fault — Causes & Fix
Updated for 2026 diagnostics & repair guidance
P0278 at a Glance
What it means
Cylinder 6 is producing noticeably more or less power than the others and the ECU can no longer balance it.
Most common cause
Worn injector delivering the wrong fuel quantity — the classic cause on high-mileage diesels.
Severity
Moderate — drivability suffers and the imbalance worsens as the injector wears.
Can you drive?
Yes, short term, but fuel economy and smoothness degrade and DPF loading increases.
Typical repair cost
£100-£350 per remanufactured injector fitted.
What Does P0278 Mean?
P0278 means the ECU's cylinder-balance monitor detected that cylinder 6's contribution to crankshaft acceleration is outside the window it can correct with fuel trim. On common-rail diesels the dominant cause is an injector delivering too much or too little fuel — wear in the nozzle and control valve changes the delivered quantity even when the coil and circuit are fine.
Common Causes
Injector-Related Causes
Worn injector nozzle or control valve
Internal wear changes the fuel quantity cylinder 6 receives, unbalancing it against the other cylinders.
Excessive injector back-leak
A worn injector returns too much fuel to the tank, starving its cylinder under load.
Injector coding mismatch
A previously replaced injector that was never coded leaves the ECU trimming from wrong baseline values.
Other Possible Causes
Low compression on the cylinder
Valve or ring wear reduces the cylinder's mechanical contribution — rule out with a compression test.
Symptoms Drivers Notice
- Uneven or lumpy idle
- Vibration felt through the cabin
- Sluggish response and higher fuel consumption
- Engine management light on
Vehicles Commonly Affected
Can You Still Drive with P0278?
Yes for short journeys, but the imbalance loads the DPF with soot and accelerates wear. Book a leak-off test soon.
How Mechanics Diagnose P0278
- 1
Read cylinder-balance live data
Check smooth-running values to confirm which cylinder deviates.
- 2
Run an injector leak-off test
Compare return volumes across all cylinders.
- 3
Check injector correction values
Compare the cylinder 6 injector's ECU corrections against its neighbours.
- 4
Compression-test the cylinder
Rule out valve or ring wear as a mechanical cause.
Repair Solutions & Costs
Replace the cylinder 6 injector
Fit a bench-tested remanufactured unit when leak-off or correction values are out of range.
Code the injector and clear adaptations
Write the calibration code to the ECU and reset adaptation values.
Address compression faults separately
Investigate valve or ring wear if the mechanical test fails.
Replacing injectors? Browse our remanufactured diesel injectors, reconditioned injectors or refurbished diesel injectors — all bench-tested with a 12-month warranty.
When Injector Replacement Is Required
When leak-off volume or ECU correction values for the cylinder sit clearly outside the range of the other cylinders, the injector is worn internally and replacement is the reliable fix.
Compatible Remanufactured Injectors
OEM bench-tested injectors for engines affected by P0278 — verified pricing, 12-month warranty, free UK delivery.
Bosch 0445116022
Bosch 0445116022 remanufactured piezo common-rail diesel injector for the Volkswagen Group 3.0 V6 TDI engine (OE 059130277BE) — Audi A4/A5/A6/A7/Q5/Q7, VW Touareg and Porsche Cayenne. Professionally tested and calibrated to OEM specification. Includes: OEM Tested, 12 Month Warranty, Free UK Delivery.
Fits: CAMA, CAMB, CAPA, CASA
View injector
Bosch 0445110047
Remanufactured Bosch 0445110047 diesel injector for BMW M57 3.0d early Common Rail solenoid applications. Direct replacement for BMW 3 Series (E46), 5 Series (E39) and X5 (E53) with M57D30 and 306D1 engines. Cross-references 0445110266, 0445110039, 0986435022, 13537785573, 13537785984 and 13534701464. Not interchangeable with newer M57N/N2 piezo or N57 generation injectors. OEM-tested and calibrated with full flow and leak-back verification on CR318 PRO test bench. Includes 12-month unlimited-mileage warranty. Supplied as an exchange unit — return your old injector within 30 days.
Fits: M57D30
View injector
Bosch 0445110616
BMW 2.0L / 3.0L Diesel Remanufactured Common-Rail Injector (N47/N57)
Fits: N57D30A
View injectorCompatible Injector Part Numbers
6 injectors compatible with engines affected by P0278.
Cross Reference Numbers
OEM and alternative part numbers for injectors affected by P0278.
Affected Vehicle & Engine Combinations
Trusted Injector Families for These Engines
Verified remanufactured injector families fitted to engines documented to log P0278.
Need a Replacement Injector?
UK-tested remanufactured injectors with 12-month warranty. Search by engine code or vehicle registration.
Need it fast? Same-day dispatch on in-stock injectors.
Order before 2pm for next working day delivery (UK mainland). Call us on 020 3355 6581.
Engine-Specific Guides
Frequently Asked Questions
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Fault Codes
Why It Happens
Common-rail injectors live at extreme pressures with clearances measured in microns. Fuel quality, heat cycles and mileage wear the internal control valve and nozzle: back-leak rises, spray patterns deteriorate and delivery drifts from calibration. Most 'engine' complaints on high-mileage diesels trace back to this gradual injector wear.
Professional Diagnosis
Workshops follow a fixed order: scan for codes and freeze-frame data, compare requested vs actual rail pressure on live data, read cylinder balance corrections, then run a comparative leak-off test. That sequence identifies the faulty injector without guesswork — and prevents needlessly replacing pumps, sensors or the wrong injector.
Typical Workshop Findings
The most frequent findings are: one injector returning several times the leak-off volume of its neighbours; carbon build-up from a failed copper washer; corroded injector connectors; and missing injector coding after a previous repair. Genuine high-pressure pump failures are rarer than back-leak faults that mimic them.
When to Replace Injectors
Replace when testing proves internal wear: leak-off clearly above the other injectors, balance corrections at their limits, or a failed bench test. Cleaning and additives cannot restore worn internal clearances. Bench-tested remanufactured injectors restore original calibration at a fraction of the new price — always coded to the ECU where the engine requires it.
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