Fuel & air metering · Powertrain · generic (SAE-defined)
P0203: Injector Circuit/Open - Cylinder 3
P0203 means there is an open or otherwise faulty electrical circuit to the cylinder 3 fuel injector, which can leave that cylinder without fuel.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0203 sets
Each time the powertrain control module (PCM) energizes and releases the cylinder 3 injector, it expects a characteristic electrical signal on that circuit. If the signal indicates an open circuit, short or missing response, the PCM sets P0203. Detection logic is manufacturer-specific.
Common causes of P0203
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Open coil inside the cylinder 3 injector
- Wiring damaged by heat, rodents or previous repairs
- Corroded or loose injector connector
- Injector power circuit or fuse fault
- PCM injector driver fault
P0203 symptoms
- Check engine light on, possibly flashing
- Engine shake and rough idle
- Loss of power, especially under load
- P0303 misfire code may be stored
How P0203 is diagnosed
- Scan for codes, noting P0303 and any other injector circuit codes.
- Inspect the cylinder 3 connector and harness for damage, including rodent chewing.
- Measure injector coil resistance and compare with other injectors.
- Check for an injector pulse with a noid light during cranking.
- Test the power feed and the control wire continuity to the PCM.
Typical fixes for P0203
- Replace the cylinder 3 fuel injector
- Repair wiring or connector damage
- Fix the injector power supply or fuse
- Repair the PCM if its driver has failed
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0203 FAQ
What does code P0203 mean?
P0203 means there is an open or otherwise faulty electrical circuit to the cylinder 3 fuel injector, which can leave that cylinder without fuel. The standard definition is "Injector Circuit/Open - Cylinder 3."
Can I drive with a P0203 code?
Keep driving to a minimum until it is repaired. A cylinder 3 that is not firing causes rough running and can damage the catalytic converter; stop driving if the check engine light flashes.
Could rodents cause P0203?
Yes. Rodents sometimes chew engine wiring, and a damaged injector wire can open the circuit and set this code, so inspect the harness closely.
What happens if I ignore P0203?
The engine will keep misfiring on cylinder 3, wasting fuel and sending unburned air and fuel into the exhaust, which can eventually damage the catalytic converter.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.