P0209

What it means

P0209 means the engine control unit has detected an electrical fault in the control circuit for the injector on cylinder 9. The unit monitors the injector driver and circuit, and sets the code when current, voltage or resistance falls outside the expected range. It only applies to engines with nine or more cylinders, typically V10 and V12 layouts, and cylinder numbering varies by engine.

Symptoms

• Engine misfire or rough running, especially at idle
• Illuminated check engine light
• Loss of power and hesitation under acceleration
• Raised fuel consumption
• Smell of unburnt fuel from the exhaust
• Engine running in a reduced-power or limp mode in some cases

Possible causes

• Faulty cylinder 9 fuel injector (open or shorted coil winding)likely
• Damaged, chafed or corroded wiring between the injector and the control unitlikely
• Poor connection or corroded terminals at the injector connector or control unit pluglikely
• Short to earth, short to voltage or open circuit in the injector feed or control wirepossible
• Blown fuse or fault in the injector power supply or relaypossible
• Failed injector driver inside the engine control unitrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for other injector or misfire codes.
2. Confirm which physical cylinder is cylinder 9 on this engine, as numbering and bank layout depend on the model.
3. Visually inspect the injector connector, wiring loom and nearby harness for chafing, heat damage, oil contamination and corrosion.
4. Check the relevant fuse and injector power supply for correct voltage with the ignition on.
5. Measure the injector coil resistance and compare it with the manufacturer's specification for that engine.
6. Test the injector wiring for continuity, and for shorts to earth or voltage, with the connector disconnected from both ends.
7. Use a scan tool's active test or a noid light or scope to confirm the control unit is sending a proper injector pulse.
8. Swap the injector with a known good one on another cylinder, if accessible, and see whether the fault follows the injector.

How to fix

• Replace the faulty cylinder 9 injector and clear the code, then confirm it does not return.
• Repair or replace damaged wiring and renew any corroded or loose connector terminals.
• Replace the blown fuse or faulty relay after finding out why it failed.
• Restore the injector power supply or earth connection if testing finds a fault there.
• Repair or replace the engine control unit only after wiring and injector faults have been ruled out and the driver fault is confirmed.

Can I keep driving?

Nearby codes

• P0208GenericCylinder 8 Injector A Circuit
• P020AGenericCylinder 1 Injection Timing