OBD-II Diagnostic Trouble Code
P0285 — Cylinder 9 Injector Circuit Low
P0285 means the ECM detected a low voltage or low current condition in the cylinder 9 injector control circuit, usually a short to ground or shorted injector coil. It only applies to engines with nine or more cylinders, such as V10 gas engines used in some medium-duty trucks; on a six- or eight-cylinder truck, suspect a code lookup or translation error and confirm with OEM software.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Cylinder 9 Injector Circuit Low
Code
P0285
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
What this means for truckers
Stop within ~50 miles on a Cummins X15, Detroit DD15, PACCAR MX-13. Driving longer risks damaging adjacent components (turbo housing, head gasket, aftertreatment) and turning a $300 fix into a $3,000 fix.
Before you replace parts — try this first
P0285 on the Fuel system is most often cylinder 9 injector wiring shorted to ground — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Cylinder 9 runs weak or dead, causing a steady miss, rough idle, vibration and low power. A misfire code for cylinder 9 often sets at the same time.
Common causes
- CommonCylinder 9 injector wiring shorted to ground ($150–$700)
- CommonShorted cylinder 9 injector coil ($200–$600)
- OccasionalContaminated or damaged injector connector ($100–$300)
- RareECM injector driver failure ($800–$2500)
How to fix
Confirm the engine actually has a cylinder 9 and the scan tool is reading the correct engine profile.
When to use: When the code appears on an engine with fewer than nine cylinders.
Measure cylinder 9 injector resistance and check for short to ground.
When to use: First electrical test.
Repair the harness or connector.
When to use: When the short is in the wiring.
Replace the cylinder 9 injector.
When to use: When the coil is shorted.
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0200 — Injector Circuit Malfunction
- → P0201 — Injector Circuit Malfunction - Cylinder 1
- → P0202 — Injector Circuit Malfunction - Cylinder 2
- → P0203 — Injector Circuit Malfunction - Cylinder 3
- → P0204 — Injector Circuit Malfunction - Cylinder 4
Frequently Asked Questions
Can I drive with code P0285?
Drive with caution. P0285 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0285 on a commercial truck?
Total repair cost ranges $100–$2500 depending on the root cause. The cheapest fix is usually the first one listed below — Cylinder 9 injector wiring shorted to ground — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0285 fail a DOT inspection?
P0285 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0285 and related codes?
P0285 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0285 is set without the companions, the issue is more isolated.
How do I prevent P0285 from coming back after a repair?
For P0285 (Cylinder 9 Injector Circuit Low), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.