P0285: Fuel injector circuit for cylinder 9 reads low voltage
Cylinder 9 injector circuit low
Severity: Severity not verified — if the car runs badly, have it inspected
The sources describe the symptoms but do not rate how urgent the code is, so no severity has been assigned.
P0285 in short
P0285 means the engine computer detected low voltage in the fuel injector circuit for cylinder 9. TroubleCodes.net lists a faulty or plugged injector, wiring or connector faults, low battery voltage, and rarely the computer as causes. Expect a rough-running engine, less power and worse fuel economy.
The engine computer drives each injector and watches its circuit. If the circuit voltage for cylinder 9 drops below the expected range, it stores P0285.
TroubleCodes.net says the fault can come from the injector itself, its wiring and connector, or low system voltage, so check those before suspecting the computer.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Faulty or plugged fuel injector
Common general cause- Why it ranks here
- TroubleCodes.net lists a faulty fuel injector among the probable causes.
- What would change this
- Rises if the injector does not click or its coil reading is out of spec. Falls if it clicks and reads normal.
Cause 2: Wiring, connector or corrosion fault at the injector
Common general cause- Why it ranks here
- TroubleCodes.net lists shorts to ground, loose or corroded connectors and poor connections; the code title points to a circuit problem.
- What would change this
- Rises if the connector is loose or corroded or the harness is damaged. Falls if wiring and connectors are sound.
Cause 3: Low battery voltage
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists low battery voltage as a possible cause.
- What would change this
- Rises if battery or charging voltage is low. Falls if system voltage is normal.
Cause 4: Engine computer (PCM/ECM) injector driver fault
Possible — needs testing- Why it ranks here
- TroubleCodes.net lists the engine computer last, as a less likely cause.
- What would change this
- Rises only after the injector and wiring test good. Falls if any other cause is found.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all stored codes and freeze-frame data, and note any other injector or misfire codes.
IfOther injector or misfire codes are stored
It meansLook at shared wiring or power supply.
IfOnly P0285 is stored
It meansFocus on the one injector and its connector.
Step 2: Inspect the injector connector and harness for looseness or corrosion, then listen for a click at the injector with a screwdriver handle held to your ear.
Warning:Keep clear of belts, fans and hot exhaust parts while the engine runs, and do not pierce or short the harness.
IfConnector is loose or corroded
It meansA wiring fault is likely.
Points to: Wiring, connector or corrosion fault at the injector
IfNo click from the injector
It meansTest for power at the injector.
IfInjector clicks normally
It meansCheck battery voltage and look for an intermittent fault.
Step 3: Use a voltmeter to check for power at the injector terminals and confirm the computer is driving the injector.
Warning:Back-probe connectors gently and keep leads from shorting adjacent pins, which can damage the injector driver or computer.
IfPower present but no drive signal
It meansThe injector or computer driver is suspect.
IfPower missing
It meansTrace the wiring back toward the source.
Points to: Wiring, connector or corrosion fault at the injector
Symptoms
- Check engine light on
- Rough-running engine
- Loss of power, especially when accelerating
- Engine knock
- Noticeably worse fuel economy
How to fix
Parts and cost context
- Fuel injector:Confirm the injector fault with tests before buying one. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P0285 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0285 yet.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error