Fuel and air

P0209 — Injector Circuit/Open – Cylinder 9

Severity: medium Drive with care, to a shop

What P0209 means

The engine control module fires each injector by switching its circuit to ground in short pulses, and it monitors the voltage and current in that circuit. P0209 is set when the cylinder 9 injector circuit looks open or reads out of range. The cause can be the injector itself, its wiring or connector, or the driver inside the module. This code applies to engines with nine or more cylinders, typically V10 and V12 layouts; check your service manual for cylinder numbering.

Symptoms

  • Check Engine light on
  • Rough idle or misfire on cylinder 9
  • Loss of power or hesitation when accelerating
  • Worse fuel economy
  • Engine vibration
  • Stalling in severe cases

Possible causes

  1. Failed cylinder 9 fuel injector (open coil)
  2. Open or shorted wiring in the injector harness
  3. Corroded, loose or damaged connector
  4. Poor ground or missing power supply to the injector
  5. Failed injector driver in the ECM/PCM
  6. Intermittent wiring fault from vibration or a chafed harness

How to diagnose

  1. Scan all codes and freeze frame data and look for other injector or power supply codes
  2. Confirm which physical cylinder is number 9 for your engine
  3. Inspect the injector connector and harness for chafing, corrosion, oil or heat damage
  4. Check for injector pulses with a noid light or listen with a stethoscope
  5. Measure injector coil resistance and compare it to the factory specification
  6. Check for power and ground at the connector and test wire continuity back to the module
  7. Swap the injector with a neighboring cylinder: if the fault follows, the injector is bad
  8. If wiring and injector test good, suspect the ECM/PCM driver

Common fixes

  • Replace the cylinder 9 injector
  • Repair the wiring or replace the damaged connector
  • Restore the power or ground connection to the injector circuit
  • Repair or replace the ECM/PCM if the driver has failed

Questions and answers

What does P0209 mean?

The engine computer detected a fault in the electrical circuit of the cylinder 9 fuel injector, such as an open circuit or out-of-range voltage or resistance. Check the injector, wiring and connector.

Can I drive with P0209?

Only for a short distance to a shop, and without heavy load. Driving long with a misfiring cylinder can damage the catalytic converter and wastes fuel.

Do I always need a new injector for P0209?

No. Wiring and connectors are common culprits. Measure the injector's resistance and check the harness, power and ground before replacing parts.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.