P0285
Cylinder 9 Injector Circuit LowP0285 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 9 Injector Circuit Low. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0285 means
P0285 is stored when the PCM/ECM detects a voltage level below the manufacturer's minimum threshold on the fuel injector driver circuit for cylinder 9. The control module continuously monitors the current loop on each injector and flags a low-circuit condition when the signal falls outside calibrated limits, preventing proper injector actuation and disrupting fuel delivery to that cylinder.
This code is exclusive to engines with nine or more cylinders — primarily V10 platforms such as the BMW S85, Dodge Viper V10, Ford 6.8 L Triton, Lamborghini Gallardo/Huracán, and Audi R8 V10, as well as V12 configurations. Because cylinder 9 sits at the far end of a long wiring harness on these large-displacement engines, the circuit is especially vulnerable to connector corrosion, chafed insulation, and ground resistance buildup over time.
Common electrical causes include an open or high-resistance injector wiring harness, a corroded or backed-out connector pin at the injector body, a failed internal PCM driver transistor (MOSFET), or a poor chassis ground connection. A mechanically restricted or completely failed injector can also create an apparent circuit-low condition if coil resistance falls outside spec. Left unaddressed, the misfiring cylinder can overheat the catalytic converter and cause long-term mechanical wear.
Common causes
Most-frequently reported root causes when P0285 is logged.
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1
Open or high-resistance wiring in the cylinder 9 injector harness between the PCM and injector connector.
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2
Corroded, backed-out, or broken terminal pins at the cylinder 9 injector electrical connector.
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3
Failed internal PCM/ECM injector driver transistor (MOSFET) for cylinder 9.
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4
Poor chassis or engine block ground connection elevating circuit ground potential.
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5
Faulty fuel injector with out-of-specification internal coil resistance on cylinder 9.
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6
Chafed or pinched wiring harness causing intermittent or sustained short to ground.
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7
PCM software fault or corrupted flash causing incorrect low-voltage threshold interpretation.
Symptoms drivers notice
How to diagnose P0285
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scan tool, record all stored and pending codes, and capture freeze-frame data before clearing.
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2
Inspect the cylinder 9 injector wiring harness and connector for corrosion, pushed-out pins, chafing, or heat damage.
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3
With the ignition on and engine off, measure supply voltage at the injector connector; expect approximately 12 V on the power feed terminal.
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4
Back-probe the PCM injector driver pin for cylinder 9 and verify the commanded pulse signal during cranking or idle using a multimeter or oscilloscope.
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5
Measure injector coil resistance at the injector body; compare against the manufacturer's specification (typically 12–16 Ω for port injectors, 1–3 Ω for GDI).
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6
Check chassis and engine block ground straps for resistance; values above 0.1 Ω indicate a ground fault that must be corrected.
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7
If all wiring, grounds, and injector tests pass, suspect the PCM internal driver circuit and consult manufacturer TSBs before authorising module replacement or reflash.
Related powertrain codes
- P0065 — Air Assisted Injector Control Range/Performance
- P0066 — Air Assisted Injector Control Circuit or Circuit Low
- P0067 — Air Assisted Injector Control Circuit High
- P0087 — Fuel Rail/System Pressure - Too Low
- P0088 — Fuel Rail/System Pressure - Too High
- P0089 — Fuel Pressure Regulator 1 Performance
Frequently asked questions
Which vehicles can trigger P0285?
Only engines with nine or more cylinders can set this code. Common examples include the BMW S85 V10 (E60 M5/E63 M6), Dodge Viper V10, Ford 6.8 L Triton V10, Lamborghini Gallardo and Huracán V10, Audi R8 V10, and various V12 platforms.
Can I drive with P0285 active?
Short distances are possible if the engine runs smoothly, but continued driving with cylinder 9 misfiring risks overheating the catalytic converter, fouling the oxygen sensors, and causing internal engine damage. Diagnose and repair promptly.
Is P0285 always an injector problem?
No. The code indicates a low-circuit voltage condition that can originate in the wiring harness, connector, ground circuit, or PCM driver — not necessarily a failed injector. Electrical checks should be completed before replacing any mechanical parts.
What is the difference between P0285 (Low) and P0286 (High)?
P0285 means the PCM sees voltage or current below its minimum threshold on the cylinder 9 injector circuit, typically caused by an open circuit or high resistance. P0286 means the signal is above the maximum threshold, usually caused by a short to voltage or a shorted injector winding.
Disabling P0285 in software
RaceTune can permanently disable P0285 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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