Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.

P0203: Injector circuit fault, cylinder 3

The engine control unit has detected an electrical problem in the control circuit for cylinder 3's fuel injector.

What P0203 means

The engine control unit has detected an electrical problem in the control circuit for cylinder 3's fuel injector. The fault may be an open circuit, a short circuit, excessive resistance, a poor connection or an internal electrical failure in the injector. P0203 does not by itself prove that the injector is blocked or needs replacing.

Can I still drive?

Treat this as urgent and avoid routine driving until it has been diagnosed. If the injector is not being controlled correctly, the engine may misfire, stall or lose power, and unburnt fuel may damage the catalytic converter. A short, gentle journey directly to a nearby garage may be reasonable only when the engine-management light is steady, the engine is running almost normally, acceleration remains safe, and there is no fuel smell, visible leak, smoke or significant loss of power. Stop the engine and arrange recovery if the light flashes, the engine shakes badly, it repeatedly stalls, power falls substantially, or fuel can be smelt or seen.

Symptoms

Engine-management light
Rough idle, hesitation or a cylinder-specific misfire
Reduced acceleration or limp mode
Difficult starting or stalling
Higher fuel consumption
Fuel smell or unusual exhaust smoke in some failure modes
No obvious symptom if the electrical fault is intermittent

Common causes

Loose, corroded, oil-contaminated or heat-damaged injector connector
Chafed, trapped, broken or shorted wiring
High resistance in a terminal, splice or earth connection
Failed injector solenoid or another internal injector electrical fault
Loss of a shared injector power supply through a fuse, relay or wiring fault
Previous engine work that disturbed or stretched the loom
Engine-control-unit injector-driver fault, which is possible but less common

Safe first checks

Record P0203, all companion codes and freeze-frame data before clearing anything.
Confirm cylinder numbering for the exact engine; do not assume where cylinder 3 is located.
With the ignition off and engine cool, look for a loose connector, broken locking tab, damaged insulation or contamination around the accessible injector wiring.
Check only the injector-related fuses identified by the handbook, and never fit a higher-rated fuse.
If there is liquid fuel, wetness around an injector or a strong fuel smell, do not restart the engine.
Do not loosen fuel pipes, probe a running injector circuit or apply battery voltage to an injector. Direct-injection petrol and common-rail diesel systems can retain dangerous pressure.
Ask the garage to confirm circuit integrity and injector electrical condition before authorising parts.

Typical UK fix cost

Allow approximately £90–£250 for diagnosis and a small connector or local wiring repair; £180–£450 for many conventional petrol-injector replacements; or roughly £300–£800 per injector where a petrol direct-injection or common-rail diesel injector, seals and coding are required. A seized injector, extensive loom damage or control-unit repair can take the total above £1,000. These are broad editorial estimates, not quotations, and must be checked against the exact vehicle, region, VAT treatment and current labour rate before publication.

Related models

This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.

Related fault codes

Sources

A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.