P0203 — Cylinder 3 Injector A Circuit/Open

The ECU detects an electrical fault in the circuit for cylinder 3. This concerns injector control, not proof of a blocked nozzle or poor mechanical cylinder contribution.

Affected system: Powertrain

Symptoms

• Rough idle, misfire or vibration if cylinder injection is interrupted.
• Engine warning lamp; reduced power or hard starting depending on affected cylinders.

Possible causes

• Loose connector, damaged terminals or open/shorted wiring for cylinder 3.
• Injector electrical fault or, less commonly, driver fault; a shared supply problem can affect multiple cylinders.

What to check

• Confirm cylinder numbering and injector type; identify the circuit for cylinder 3 on the diagram rather than assuming location.
• Save codes and failure conditions; if several injectors are affected, check shared supplies/connections first.
• Inspect connector and wiring for cylinder 3, including terminal retention and vibration/chafing areas.
• With power off and modules isolated as instructed, test for opens and shorts between injector and ECU.
• Test injector and command waveform using compatible equipment and OEM limits; do not apply battery voltage directly, then verify the repair.

Also written as: P0203-00, P020300, PO203 (some scan tools add the fault-type byte, e.g. -00).