P0203

What the code means

Code P0203 points to a fault in the cylinder 3 fuel injector circuit. The engine control unit (DME) detected an electrical problem — an open circuit, a short, or incorrect resistance in the injector control circuit. This disrupts fuel delivery to cylinder 3, which causes misfires and rough running.

The affected system is the direct-injection fuel system. The main components are the cylinder 3 fuel injector, the wiring harness, the connectors, and the DME.

Symptoms

• Engine: misfires in cylinder 3, rough idle, loss of power
• Indicators: Check Engine Light (CEL) on
• Conditions: symptoms may be constant or get worse under load

Diagnosis and repair

Step 1: Visual inspection of the wiring

Check the wiring harness and the cylinder 3 injector connector for damage, corrosion, or loose contacts.

Step 2: Check injector resistance

Disconnect the connector and measure resistance across the injector terminals. Compare with the reference values (usually 10–18 ohms for direct-injection injectors).

Step 3: Replace the injector

If resistance is out of spec or the wiring checks out, replace the cylinder 3 fuel injector. Use the original BMW part (13647597801). After replacement, run the injector adaptation through ISTA.

Common mistakes: replacing the injector without checking the wiring — the problem is often a damaged harness, not the injector itself.

Secondary problems

Ignoring P0203 can lead to:

• Catalytic converter damage: unburned fuel from cylinder 3 reaches the exhaust system, causing overheating and converter breakdown. A converter replacement is an expensive repair.
• Engine wear: running with misfires for a long time can damage the spark plugs, ignition coils, and oxygen sensors.

Severity: fix the fault as soon as possible to avoid extra costs.