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P0285 – Cylinder 9 Injector Circuit Low (OBD2)

P0285 means "Cylinder 9 Injector Circuit Low". The voltage the control unit measures in the fuel injector circuit is below the permitted minimum. For a sensor this usually means the signal wire is shorted to ground or the reference voltage is missing; for an actuator, that its control wire is shorted to ground.

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P0285 quick summary

Fault codeP0285
MeaningCylinder 9 Injector Circuit Low
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityHigh
Can I drive?Only gently. An injector that does not open causes a misfire; one that stays open can flood the cylinder, wash oil off the cylinder wall and damage the catalytic converter. Have it checked promptly.
Repair cost€20 – €1,500

How fuel injectors and their circuits work

Fuel injectors are electrically controlled valves that spray fuel into the engine; these codes mean the control unit has detected an electrical or balance fault in an injector circuit.

Each injector is opened by an electrical pulse from the engine control unit. Port-injection petrol engines use 12 V solenoid injectors; direct-injection petrol and common-rail diesel engines use high-voltage solenoid or piezo injectors controlled by special driver stages, sometimes in a separate injector control module.

The control unit monitors the current in each injector circuit. Codes P0200–P0212 report a general injector circuit fault for a cylinder, P0261–P0296 separate low and high faults per cylinder, and 'contribution/balance' codes mean that one cylinder contributes more or less power than the others, usually because the injector delivers the wrong quantity.

An injector circuit fault normally causes a misfire or rough running on that cylinder. Causes range from a damaged connector or wire to a failed injector coil or, on diesels, a worn injector that leaks or delivers the wrong amount. On direct-injection engines, injector work requires care because of the very high fuel pressure.

The code refers to cylinder 9. Cylinder numbering differs between manufacturers (and between banks on V engines), so check the numbering for your engine in the service information before replacing parts.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16669 (P0285). Both numbers mean the same fault.

Symptoms of P0285

  • Check Engine light on
  • Misfire or rough running on one cylinder
  • Loss of power, hesitation
  • Higher fuel consumption or smell of fuel
  • Smoke from the exhaust (diesel), hard starting

Most common causes of P0285 (most likely first)

Mechanic's Pro Tip

On diesels and direct-injection engines, always note the correction code printed on the new injector and enter it with the scan tool after fitting. An uncoded injector delivers the wrong quantity and can bring back the balance code – or cause smoke and rough running.

  1. 1.Signal or control wire shorted to ground

    Most likely

    Look for chafed insulation where the harness touches the engine, exhaust brackets or body edges.

  2. 2.Missing 5 V reference or supply voltage

    An open reference wire or a shorted sensor elsewhere on the same reference circuit can pull it down.

  3. 3.Internal short in the fuel injector

  4. 4.Damaged injector connector or wiring

    Heat and vibration crack connectors and wires on the injector harness.

  5. 5.Failed injector coil or piezo element

    The injector no longer opens correctly.

  6. 6.Clogged or leaking injector (balance faults)

    Deposits or wear change the delivered quantity; diesel injectors can also leak back too much fuel.

  7. 7.Fault in the injector driver or injector control module

    On some diesels the injectors are controlled by a separate module.

Step-by-step diagnostic guide

  1. 1

    Read codes and misfire data

    Read all codes, note the cylinder and check for misfire codes or injector correction values in live data.

  2. 2

    Measure the signal voltage

    With the ignition on and the fuel injector plugged in, back-probe the signal wire. Then unplug it and check the reference/supply and ground wires separately.

    Multimeter: Signal near 0 V = short to ground or no reference. Reference wire: about 5 V with ignition on. Signal wire to ground with connector unplugged: no continuity.

  3. 3

    Inspect connectors and wiring

    Inspect the injector connector and harness for damage, corrosion and chafing.

  4. 4

    Measure the injector

    Unplug the injector and measure its resistance; compare with a neighbouring injector and the specification.

    Multimeter: High-impedance port injectors: about 11–16 Ω. Low-impedance and many diesel solenoid injectors: around 0.2–3 Ω. Piezo injectors cannot be checked reliably with an ohmmeter – use the scan tool tests.

  5. 5

    Run injector tests

    Use the scan tool's injector balance, quantity correction or cylinder cut-out test. On diesels, a leak-off (return flow) test shows worn injectors.

  6. 6

    Repair and code

    Repair wiring or replace the injector. On many diesels and direct-injection engines, new injectors must be coded to the control unit with their correction code (IMA/IQA/C2I).

Frequently asked questions

Can I keep driving with P0285?

Only gently. An injector that does not open causes a misfire; one that stays open can flood the cylinder, wash oil off the cylinder wall and damage the catalytic converter. Have it checked promptly.

How much does it cost to fix P0285?

Typical repair costs are 20 € – 1500 €, depending on the cause and the vehicle. The most common fixes are: signal or control wire shorted to ground; missing 5 V reference or supply voltage; internal short in the fuel injector. Always confirm the cause with the tests above before buying parts.

Can I clean a faulty injector?

Port injectors can often be cleaned by a specialist with ultrasonic cleaning. Electrical faults and worn diesel or direct-injection injectors cannot be fixed by cleaning – they need repair or replacement.

What does 'contribution/balance fault' mean?

The control unit compares how much each cylinder speeds up the crankshaft. If one cylinder contributes much more or less than the others, it stores a balance fault – usually caused by an injector delivering the wrong quantity, sometimes by low compression.

What is the difference between P0285 and similar codes?

P0285 belongs to a group of codes for the same component that differ in the type or location of the fault: P0282 – Cylinder 8 Injector Circuit Low; P0283 – Cylinder 8 Injector Circuit High; P0284 – Cylinder 8 Contribution/Balance Fault; P0286 – Cylinder 9 Injector Circuit High; P0287 – Cylinder 9 Contribution/Balance Fault; P0288 – Cylinder 10 Injector Circuit Low. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.