What does it mean?
P1233 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Fuel Injector 4 Control Circuit Shorted .
Symptoms
- Check engine lamp on, flashing under load when the misfire is severe
- Misfire, shake and rough idle traced to cylinder 4
- Black smoke, fuel smell and an obviously rich mixture
- Fuel washing into the oil, so the level rises and the oil smells of fuel
- Power loss, hard starting, and several dead cylinders if the shared fuse has blown
Likely causes
- Injector wire chafed against metal, shorting the control line to ground or to a live conductor
- Injector winding shorted internally, giving a resistance well below specification
- Contaminated connector where oil, coolant or water bridges the terminals
- Loom crushed or pinched by a bracket, clamp or a refitted component
- Damaged terminal that has deformed and touches the connector shell
- Injector driver in the module destroyed by the short, sometimes taking the fuse with it
How to fix it
- Check the injector fuse and read all codes to see how many cylinders are involved
- Unplug injector 4 and measure the control wire both to ground and for battery voltage with the ignition on
- Ohm the injector itself and compare with the others; a low reading confirms an internal short
- Inspect the connector for oil and moisture and test each pin against the injector body
- Follow the harness and repair any chafe, crush or heat damage found
- Replace the injector only after the wiring is proven, then clear the codes and watch the misfire counter
- Test the module driver output last, once the external short has been removed