OBD codes / P0291
P0291
ModerateCylinder 11 Injector Circuit Low
A V12 hides one dead cylinder so thoroughly that the only sign may be the warning light — but cylinder 11's unburned fuel is still flowing into that bank's catalytic converter. Treat the light as the symptom and repair promptly; a flashing light means stop driving.
What this code means
Cylinder 11 exists only on engines with eleven or more cylinders, so P0291 is effectively a V12 code (including W12-style layouts). It sets when the ECM measures voltage below the expected range on the cylinder 11 injector control circuit — the electrical signature of a short to ground, an open circuit, or an injector coil that has shorted internally. As with the whole P0261–P0296 family, this is a circuit diagnosis: a mechanically clogged injector would starve the cylinder without disturbing the voltage the ECM monitors, producing a misfire code instead. Twelve identical injector circuits make comparison testing the natural approach — resistance-check cylinder 11's injector against any neighbor and inspect its harness leg and connector. Companion codes are P0211 (cylinder 11 injector circuit) and P0311 (cylinder 11 misfire). Twelve-cylinder bank numbering differs by manufacturer, so identify cylinder 11's physical position from your engine's documentation before testing.
Symptoms you might notice
- Misfire on cylinder 11 — often nearly imperceptible on a V12
- Faint idle unevenness or high-rpm coarseness
- Slight power and refinement loss
- Check-engine light, flashing under sustained misfire
- May be entirely symptom-free if intermittent
What it costs to fix
Typical range: $60–$450 · about ~0.5–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Fuel injector (single) | $50–$300 | ~0.5–2 hrs |
| Wiring/connector repair | $5–$50 | ~0.5–2 hrs |
Twelve-cylinder engine bays are the tightest of all: expect labor at or beyond the top of the range once intake plumbing and covers come off, and direct-injection injectors for these engines carry premium pricing. Wiring repairs remain cheap in parts.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0291 for my exact vehicle →
Frequently asked
Why have I never heard of P0291?
Because very few engines can set it. Cylinder 11 exists only on twelve-cylinder (and similar) engines, so this code lives almost exclusively on luxury and performance V12s. On any smaller engine, a reported P0291 deserves skepticism about the scan data.
What does the ECM see before setting P0291?
Lower-than-expected voltage on the cylinder 11 injector circuit while pulsing it — consistent with a short to ground, broken wiring, or an injector coil shorted internally. The high-voltage version of the same monitor is P0292.
Can I ignore it since the car runs perfectly?
No — smooth running is exactly what a V12 does with a dead cylinder. Meanwhile unburned fuel is heating that bank's catalytic converter, and exhaust repairs on twelve-cylinder cars are notoriously expensive. Fix the cheap electrical fault before it creates a costly one.
How do I know if the injector or the harness failed?
Measure the cylinder 11 injector's resistance and compare with a neighbor. Matching values clear the injector and implicate the harness or connector; a shorted or open reading condemns the injector. On these engines, do the measurement before any teardown you can avoid.
Seeing P0291 on your car? Get a diagnosis specific to your exact year, make and model.
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.