What does it mean?
P1203 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder 3 Fuel Injection Circuit Electrical Malfunction .
Symptoms
- Check engine light on, usually together with a cylinder 3 misfire code
- Engine shakes at idle and runs unevenly at low speed
- Poor acceleration, hesitation and a general lack of power
- Difficult starting, particularly on a cold engine
- Unburnt fuel smell from the exhaust
- Increased fuel consumption and a risk of catalytic converter damage if left unrepaired
Likely causes
- Open or shorted injector winding on cylinder 3
- Damaged, corroded or loose injector connector
- Control wire to injector 3 broken, chafed, or shorted to ground or to battery voltage
- Missing supply voltage from a blown fuse, faulty relay or corroded power splice
- Harness damage where it passes hot or moving components
- Oil migration into the connector from a leaking valve cover or injector seal
- Failed driver channel for cylinder 3 inside the control module
How to fix it
- Read all codes and note whether cylinder 3 misfire counts rise with this fault
- Check for battery voltage at the injector 3 supply pin with the ignition on
- Measure the winding resistance of injector 3 and compare it with the other cylinders
- Use a noid light or scope on the control wire while cranking to confirm the module is pulsing the injector
- Where practical, swap injector 3 with a neighbouring cylinder and see whether the fault moves with the injector
- Inspect the connector and harness for oil, corrosion, chafing and heat damage, and repair the wiring
- Replace the cylinder 3 injector if it is electrically faulty, then clear codes and confirm the engine idles smoothly with no misfire counts