OBD codes / P0285
P0285
ModerateCylinder 9 Injector Circuit Low
A V10 or V12 disguises one dead cylinder almost completely, but the catalytic converter on cylinder 9's bank still absorbs the unburned fuel. Don't let smooth running lull you — repair promptly, and stop driving if the check-engine light begins to flash.
What this code means
P0285 belongs to a rare club: it can only set on engines with at least nine cylinders, which in passenger vehicles means V10 and V12 engines. The fault itself is standard injector-circuit fare — the ECM measured lower-than-expected voltage on the cylinder 9 injector control circuit, indicating a short to ground, an open circuit, or an injector coil that has shorted internally. As with all codes in this family, it describes the electrical path, not the spray pattern; a clogged injector is a separate, mechanical problem that would surface as a misfire code instead. The many identical injector circuits on a V10 or V12 make comparison testing especially effective: measure cylinder 9's injector resistance against any neighbor. Companion codes are P0209 (cylinder 9 injector circuit) and P0309 (cylinder 9 misfire). Bank numbering on these engines varies by manufacturer, so identify cylinder 9's physical position from your engine's documentation before testing.
Symptoms you might notice
- Misfire on cylinder 9 — often subtle, since many cylinders remain
- Slight idle roughness or loss of the engine's usual smoothness
- Reduced power, more evident at high load
- Check-engine light, possibly flashing under sustained misfire
- Sometimes no perceptible symptoms 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 |
V10 and V12 engine bays are tight, and reaching an inner-bank injector frequently means removing the intake and other hardware — labor runs to the high end. Direct-injection injectors on these engines also cost more than the range's low figure suggests.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0285 for my exact vehicle →
Frequently asked
My car only has 4, 6, or 8 cylinders — can it set P0285?
No. Cylinder 9 exists only on engines with nine or more cylinders — V10s and V12s in practice. If a scanner shows P0285 on a smaller engine, suspect a scan-tool misread or a stored code from a module mismatch rather than a real cylinder 9 fault.
What does the 'low' in P0285 indicate?
Circuit voltage below the ECM's expected range while it drives the cylinder 9 injector — typical of a short to ground, broken wiring, or an injector coil shorted internally. Its sibling P0286 covers the opposite, high-voltage direction.
The engine feels perfectly smooth. Do I still need to fix it?
Yes. Twelve- and ten-cylinder engines mask a single misfire so well you may feel nothing, but unburned fuel from cylinder 9 is still flowing into that bank's catalytic converter. Converter damage is a far costlier repair than the injector or wiring fix.
Is this the injector itself or the wiring to it?
Testing decides it: measure the cylinder 9 injector's resistance against a neighbor. A matching reading points at the harness or connector; a shorted or open reading points at the injector. On these engines, check connector condition first — access work is the expensive part.
Seeing P0285 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.