OBD-II Code
P0278
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$200–$5,500
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$200 (single glow plug + injector clean) to $5,500 (head pull and injector cup replacement on a Cummins).
P0278 means the cylinder-balance monitor flagged cylinder 6 for contributing outside the +/- 5 mm3/stroke deviation window the ECM allows on per-cylinder fuel trim.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP0278 means the cylinder-balance monitor flagged cylinder 6 for contributing outside the +/- 5 mm3/stroke deviation window the ECM allows on per-cyli…
P0278 means the cylinder-balance monitor flagged cylinder 6 for contributing outside the +/- 5 mm3/stroke deviation window the ECM allows on per-cylinder fuel trim. Diagnostic flow is identical to any contribution/balance code, but cylinder-6 location matters: on most domestic V8s (Ford modular, GM LS, Chrysler Hemi) cylinder 6 is on the left (driver) bank, second from the front; on a Ford Powerstroke 6.0L/6.4L/6.7L V8, the bank assignments follow the standard 1-3-5-7 right / 2-4-6-8 left layout; on a Duramax LB7-LML 6.6L V8, cylinder 6 is on the left bank rear; on a Cummins inline-6, cylinder 6 is the rear-most cylinder closest to the firewall.
Cheapest-first ladder
- pull live cylinder balance data, look for cyl 6 deviation past +/- 5 mm3, then run a manual cylinder cutout test (disable cyl 6 injector and watch RPM drop — a healthy cylinder drops idle RPM by 80-150 RPM; a weak cylinder drops less than 50 RPM).
- Next: glow plug current draw on diesels (a shorted glow plug skews thermal balance), compression test (looking for less than 85% of highest), injector return-flow test (back-leak test on common-rail diesels — a leaking injector returns 3-10x normal fuel volume to the tank).
- Expensive-misdiagnosis caveat: on inline-6 diesels especially, a cracked or eroded injector cup in the cylinder head will exactly mimic a failing injector and cost $1,800-$3,500 in head-pull labor to find after you've already replaced the injector.
Vehicle-specific patterns1998-2007 Dodge RAM 2500/3500 with the 5.9L Cummins inline-6 commonly throws P0278 on cylinder 6 specifically because it's the rear-most cylinder and…
- 1998-2007Dodge RAM 2500/3500 with the 5.9L Cummins inline-6 commonly throws P0278 on cylinder 6 specifically because it's the rear-most cylinder and sits closest to the turbo + firewall heat — injector heat-soak failure or a #6 injector cup leak (the cup is a brass sleeve that isolates the injector tip from coolant) is the classic finding.
- 2008-2010Ford 6.4L Powerstroke V8 throws P0278 from the well-documented piston cracking and EGR-cooler failure that contaminates injectors — Ford issued multiple TSBs and the affected cylinders cluster on the right bank.
- 2007-2010Duramax LMM 6.6L throws P0278 from injector body cracks at high mileage that bleed rail pressure.
- 2011-2018BMW N57 / B57 inline-6 diesel (European market and limited US) throws P0278 from EGR-cooler carbon contamination starving the rear cylinders of clean intake air.
Estimated repair$200 (single glow plug + injector clean) to $5,500 (head pull and injector cup replacement on a Cummins).
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