OBD codes / P0203
P0203
SeriousInjector Circuit/Open - Cylinder 3
Don't sit on this one. With cylinder 3 not firing, its unburned fuel ends up in the exhaust stream where it can overheat and destroy the catalytic converter. Drive gently and only as needed until it's repaired, and pull over if the check-engine light flashes.
What this code means
Every time cylinder 3 is due for fuel, the engine computer grounds that injector's circuit and expects to see a specific electrical response. P0203 sets when it doesn't — the circuit reads open, shorted, or with the wrong resistance. Keep in mind this is an electrical diagnosis, distinct from a clogged injector: a plugged nozzle flows poorly but still tests fine electrically. The usual suspects, roughly in order of likelihood and cost, are a corroded or half-seated connector at the injector, wiring chafed through against a bracket or the engine, and a failed coil winding inside the injector itself. A bad injector driver inside the engine computer is possible but rare. Expect the matching misfire code P0303 to accompany it, since cylinder 3 typically isn't getting fuel.
Symptoms you might notice
- Engine misfire concentrated on cylinder 3, usually with P0303 set as well
- Shaky, rough idle
- Sluggish acceleration — the engine feels like it's down a cylinder
- Check-engine light on, flashing if the misfire is active
- Occasional hard or slow starts
What it costs to fix
Typical range: $80–$550 · about ~0.5–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Fuel injector (single) | $50–$300 | ~0.5–2 hrs |
| Wiring / connector repair | $10–$60 | ~0.5–1.5 hrs |
Labor is the wildcard: injectors that sit in plain view take well under an hour, while engines that bury them under the intake manifold can double or triple the labor. Ranges here reflect common gasoline port and direct-injection engines; diesel injectors are substantially more expensive.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0203 for my exact vehicle →
Frequently asked
How do I tell whether P0203 is the wiring or the injector?
Unplug the cylinder 3 connector and measure the injector's resistance with a multimeter — compare it to another cylinder on the same engine. A normal reading shifts suspicion to the connector, harness wiring, or (rarely) the computer. An open or badly off reading means the injector itself has failed.
Which cylinder is number 3?
It varies by manufacturer. On an inline-four it's usually the third cylinder from the front of the engine, but V6 and V8 numbering schemes differ widely between brands. Look up the cylinder layout for your exact engine before testing or replacing parts.
Can I keep driving with P0203?
Only gently and only briefly. A dead cylinder feeds raw fuel to the catalytic converter, and converter damage costs far more than the injector-circuit fix. A flashing check-engine light is your signal to stop driving immediately.
Why would swapping injectors help diagnose this?
If you move the cylinder 3 injector to another cylinder and the circuit code follows it (becomes, say, P0202), the injector is bad. If the code stays on cylinder 3, the problem is in that cylinder's wiring, connector, or the computer. It's a reliable way to avoid buying a part you don't need.
Seeing P0203 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0203 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.