What does it mean?
P1239 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 3 Fuel Injection Circuit Open Circuit .
Symptoms
- Hard misfire on cylinder 3 and a flashing check engine lamp under load
- Engine shakes badly at idle and feels down on power
- Raw fuel and air reaching the exhaust, risking catalyst damage
- Poor acceleration and a distinctly uneven exhaust note
- Higher fuel consumption and possible stalling at idle
Likely causes
- Chafed wire that has finally parted, or a conductor broken under intact insulation
- Connector not seated, or a locking tab broken so the terminals separate under vibration
- Injector winding open after internal failure or overheating
- Corroded, burnt or spread terminals that no longer touch
- Open supply to the injector from a blown fuse, a failed relay or a bad splice
- Failed driver output inside the control module
How to fix it
- Read all codes and see whether cylinder 3 alone or a group of injectors is affected
- Check the injector supply voltage and the relevant fuse with the ignition on
- Inspect the connector for a disengaged terminal, corrosion and a broken lock tab
- Measure the injector coil resistance; an open reading condemns the injector
- Check continuity of the control wire to the module and flex the harness during the test
- Use a noid light to confirm the module is producing a pulse
- Repair or replace according to the test results, then verify with live data that the cylinder now contributes
- Consider the module driver only as a last step