P0203
Fuel injector failure, Powertrain Control Module (PCM) failure, Wiring issue.
- Audi
- 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 on an Audi means the engine control unit has detected a fault in the electrical circuit of the cylinder 3 fuel injector. It sets when the injector's drive signal or feedback is not what the control unit expects, such as an open circuit, a short, or a resistance out of range. This points to the injector, its wiring or connector, or in rare cases the control unit driver. It is an electrical fault, not a fuel delivery fault.
Symptoms
- Engine management light on, possibly flashing if misfire is severe
- Rough idle or a noticeable shake
- Misfire on cylinder 3, possibly with a P0303 stored as well
- Hesitation or loss of power under acceleration
- Poor fuel economy or a fuel smell from the exhaust
- Hard starting or engine running on fewer cylinders
Possible causes
- Faulty cylinder 3 injector (open or shorted coil, or internal fault)likely
- Damaged, corroded or loose injector connector or terminals at cylinder 3likely
- Wiring fault between injector and control unit (chafed, open circuit, short to earth or supply)possible
- Poor earth or supply voltage to the injector circuitpossible
- Heat or vibration damage to the harness near cylinder 3 or the engine bay routingpossible
- Faulty injector driver inside the engine control unitrare
How to diagnose
- Read all stored codes and freeze frame data, noting related codes such as cylinder 3 misfire or other injector circuit faults, and the conditions when it set.
- Check for any relevant technical bulletins or software updates for the specific model and engine.
- Visually inspect the cylinder 3 injector connector and the harness for damage, oil contamination, corrosion, bent pins or a poor lock.
- Disconnect the connector and check terminals for tension and condition, then clear the code and see if it returns.
- Measure the injector coil resistance and compare it with the specification for that engine, as values differ between port injection and direct injection types.
- Check the wiring for continuity and for shorts to earth or supply between the injector connector and the control unit, with the battery disconnected as needed.
- With the engine running or cranking, check the injector supply, earth and drive signal with a suitable meter or oscilloscope, following the procedure for the engine.
- Where practical, swap the injector or connector with another cylinder and see whether the fault follows it. Direct injection engines need the manufacturer's procedure for this.
How to fix
- Repair or replace damaged wiring or the connector terminals on the cylinder 3 injector circuit.
- Replace the cylinder 3 injector if its resistance or signal is out of specification, following the correct procedure and sealing parts for the engine.
- Restore poor earth or supply connections found during testing.
- Replace or repair the engine control unit only after the injector, wiring and supplies have all been proven good.
- Clear the codes and road test, checking that the misfire counters stay at zero and the fault does not return.
Can I keep driving?
Short, gentle journeys to a workshop are usually acceptable, but a misfiring cylinder can let unburnt fuel damage the catalytic converter. If the engine light flashes or the engine runs very roughly, stop driving and get it recovered.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.