What does it mean?
P1556 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 6 Injector Circuit Range/Performance .
Symptoms
- Check engine light on and a cylinder 6 misfire code often set alongside it
- Rough, shaking idle with obvious misfire when cold
- Flat spot and hesitation under acceleration
- Difficult starting after the vehicle has been standing overnight
- Increased fuel consumption and a strong exhaust smell
- Reduced power and, on some vehicles, a drop into limp mode
Likely causes
- Injector coil resistance outside the specified window, or an intermittent internal short
- Water or oil intrusion into the cylinder 6 injector connector
- Wiring rubbed through where the injector harness passes a bracket or a sharp edge at the rear of the head
- Broken conductor inside the loom that only opens when the engine is hot and moving on its mounts
- Fouled or partially blocked injector nozzle affecting the measured circuit behaviour
- Missing calibration data after an injector was swapped between cylinders
- Faulty injector driver channel in the PCM
How to fix it
- Read freeze frame data and check whether the misfire counter for cylinder 6 is climbing
- Confirm injector pulse at the connector with a test light or an oscilloscope during cranking
- Measure the coil resistance and compare it with the neighbouring injectors
- Exchange the injector with one from another cylinder to see whether the code follows the component
- Examine the harness at the rear of the cylinder head, where heat and vibration damage is most common
- Clean or replace the injector, then write the correction code if the system requires one
- Repair the harness, clear the code and verify stable cylinder contribution values afterwards