P0285Generic code

P0285 Code: Cylinder 9 Injector Circuit Low

The P0285 code means the control circuit of the cylinder 9 injector has a lower voltage than the computer expects, usually from a short to ground or a missing supply. It is a high severity fault because an injector stuck open can flood the cylinder. You can drive with caution, but only for a short time.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$20 to $600
Difficulty
Medium
System
Fuel Injection
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0285 code means

With the injector closed, its control wire should read about 12 V (the supply that arrives through the coil). If the computer sees a low voltage at that moment, it concludes that the wire is shorted to ground or that no supply is arriving. A control wire shorted to ground can hold the injector open all the time and flood cylinder 9, so this is a fault to deal with right away. The P0285 code is the computer way of flagging it.

To confirm it without special tools, unplug injector 9 with the key off and measure the resistance between the control wire (computer side) and ground. It should be very high. A reading close to zero confirms a short in the wiring. If the wiring is fine, measure the injector coil: a resistance far below that of the other injectors points to an internal short.

Cylinder numbering depends on the manufacturer. On most inline engines, cylinder 1 is the one closest to the timing belt or chain. On V engines, the odd and even cylinders are usually on different banks. Confirm the numbering in the service manual before you take anything apart.

P0285 code symptoms

  • Check engine light on.
  • Engine shaking or a rough idle.
  • Loss of power.
  • Black or white smoke (diesel) or misfires (gas engine).
  • High fuel use or a smell of fuel.

Likely causes of the P0285 code

  1. Control wire shorted to ground from rubbing against the engine.
  2. 12 V supply interrupted. Fuse, relay or supply wire.
  3. Injector 9 internally shorted. Very low resistance.
  4. Connector with water or corrosion.
  5. Damaged computer driver. Uncommon.

How to diagnose the P0285 code step by step

  1. Confirm the cylinder with the scan tool (misfire counters, or per-cylinder fuel quantity corrections on a diesel).
  2. Measure the resistance of injector 9 and compare it with the other injectors.
  3. Check for the 12 V supply at the connector with the key on.
  4. Check the control wire. Continuity to the computer, and isolation from ground and from 12 V.
  5. Use an injector test light (noid light) to see whether the computer is sending the command.
  6. Clear the codes and recreate the condition to confirm the repair.

How to fix the P0285 code

  • Repair the damaged wire or connector.
  • Replace the injector if its coil is open or shorted.
  • Repair the supply (fuse, relay, wire).
  • If the computer driver is damaged, replace the shorted injector first.
  • Clear the codes and verify on a road test.

Technical reference data

  • High-impedance gasoline injector: 11 to 18 ohms.
  • Low-impedance injector: 2 to 5 ohms.
  • Typical supply: 12 V from a relay or the computer. The computer switches the ground to open the injector.
  • Piezo common rail diesel injectors are not tested with an ohmmeter the same way. Follow the manufacturer procedure.
  • These values are for orientation only. Check the manufacturer data for your engine.

Brand-specific notes

On many vehicles the injector supply shares a fuse with the ignition coils. If several codes show up at once, check that fuse first.

Frequently asked questions about P0285

Can I drive with a P0285 code?
With caution and only for a short time. An injector that stays open can dilute the oil with fuel and damage the engine.
Which cylinder is number 9?
Cylinder numbering depends on the manufacturer. On most inline engines, cylinder 1 is the one closest to the timing belt or chain. On V engines, the odd and even cylinders are usually on different banks. Confirm the numbering in the service manual before you take anything apart.
Does the injector have to be replaced?
Only if the tests confirm it. In many cases the cause of the P0285 code is in the wiring, not in the injector.
How much does it cost to fix P0285?
Between $20 and $600 on a gas engine. On a diesel, an injector can cost $150 to $800 plus the coding.
What does the P0285 code mean?
It is a generic OBD2 code that means the control circuit of the cylinder 9 injector reads a lower voltage than expected. It usually comes from a wire shorted to ground or a lost supply.
What is the most common cause of P0285?
A control wire shorted to ground after rubbing against the engine, or a lost 12 V supply from a fuse or relay. An injector with a shorted coil is the next most likely cause.

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