P0203
Cylinder 3 Injector A Circuit.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 2
- AreaFuel and air metering (injector circuit)
- 03
- FaultThe specific fault in that area
What it means
P0203 is the generic code for a fault in the injector circuit for cylinder 3. The engine control unit drives each injector and monitors the circuit, and it has seen an open circuit, a short, or a current or voltage value outside the expected range. This points to an electrical fault in the circuit, not necessarily a mechanical fault in the injector.
Symptoms
- Engine misfire, especially on cylinder 3
- Rough idle and hesitation under load
- Illuminated engine warning light
- Reduced power or the engine running in a limited mode
- Poor fuel economy
- Hard starting or an engine that cranks but runs unevenly
Possible causes
- Faulty cylinder 3 fuel injector with an open or shorted coillikely
- Damaged, chafed or corroded wiring between the injector and the engine control unitlikely
- Loose, corroded or damaged injector connector or control unit connector pinslikely
- Poor power supply or earth to the injector circuit, such as a fuse or relay faultpossible
- Short to earth or to voltage in the harness caused by heat damage or rubbingpossible
- Fault in the injector driver within the engine control unitrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, including engine load, temperature and rpm when the fault set.
- Check for other injector, misfire or fuel trim codes, which help show whether the fault is electrical only or is also affecting combustion.
- Visually inspect the cylinder 3 injector connector and the wiring along its route for chafing, heat damage, oil contamination, corrosion and poor pin tension.
- Clear the code and see if it returns immediately or only when the engine is hot or vibrating, and gently wiggle the harness with the engine running to look for a change.
- Measure the injector coil resistance and compare it with the specification for the engine, as the value varies by model and injector type.
- Check the injector supply voltage and earth or driver signal at the connector using a multimeter or oscilloscope, following the wiring diagram for the vehicle.
- Swap the injector with another cylinder if the design allows and see whether the fault follows it, then check the wiring continuity and insulation to the control unit if it does not.
- Check the relevant fuses and relays and look for any applicable technical bulletins for the model.
How to fix
- Replace the cylinder 3 injector if its resistance, signal or operation is out of specification, following the procedure for that engine.
- Repair or replace damaged wiring, and secure the harness away from heat and sharp edges.
- Clean or replace corroded or damaged connectors and terminals.
- Restore the correct power supply or earth by repairing fuse, relay or earth connection faults.
- Have the engine control unit tested and repaired or replaced only after the wiring and injector have been proven good.
Can I keep driving?
Medium severity
The car can usually be driven a short distance to a workshop, but avoid heavy loads and long journeys. A cylinder that is not firing properly can overload the catalytic converter with unburnt fuel and may cause further damage if left.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.