What does it mean?
P1204 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 4 Fuel Injection Circuit Electrical Malfunction .
Symptoms
- Check engine lamp on, with freeze frame usually captured at idle or light load
- Rough idle and a steady misfire that follows cylinder 4
- Power loss, hesitation when accelerating and rough running under load
- Raw fuel smell from the exhaust and higher fuel consumption
- Hard starting, and in some cases the engine runs only on the remaining cylinders
Likely causes
- Corroded, spread or backed-out terminals in the cylinder 4 injector connector
- Chafed or broken wire between the PCM (powertrain control module) and the injector, often where the harness crosses a bracket or the valve cover edge
- Injector winding out of specification: open, internally shorted, or resistance far from its neighbours
- Loss of the shared battery feed to the injectors from a blown fuse, corroded splice or a relay with burnt contacts
- Oil, fuel or moisture inside the connector body creating leakage between pins
- Damaged injector driver stage inside the PCM, usually the consequence of a short left uncorrected
How to fix it
- Read all stored codes and the freeze frame; other injector codes at the same time point to a shared feed rather than one injector
- Unplug the cylinder 4 injector connector and inspect for oil, green corrosion, spread terminals and a broken lock tab
- Measure injector coil resistance and compare it with the other injectors on the same engine
- With the ignition on, check supply voltage at the connector and test the driver wire for continuity and for shorts to ground or battery
- Wiggle-test the harness while graphing the misfire counter on the scan tool to catch an intermittent fault
- Swap the suspect injector with a neighbouring cylinder; if the fault follows the injector, renew it
- Evaluate the PCM driver stage only after wiring and injector both test good