P0203 code: Injector Circuit/Open - Cylinder 3
P0203 means injector Circuit/Open - Cylinder 3. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0203 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.
P0203 symptoms
- 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 P0203
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 →
How to fix P0203
Moderate — doable at home with common tools and patience
- Read freeze frame and the cylinder 3 misfire data
Note when the code set — cold start, idle, or under load — and whether P0303 or a cylinder 3 misfire count came with it. A hard fault that returns the moment you clear it is usually a clean break or a dead winding; one that takes days to come back suggests a connection that only drops out with heat or vibration.
- Find the middle injector and check it by sight
On a four-cylinder, cylinder 3 is one of the two middle positions, often under the intake runners or throttle-body plumbing where the connector is easy to knock loose and hard to see. On V engines it depends on the maker's numbering. Use a mirror and flashlight to confirm the plug is seated and its clip intact.
- Check the terminals for proper grip
Unplug injector 3 and inspect the female terminals for corrosion or spreading. A matching male test pin should drag slightly as it slides in; a loose fit can lose contact when hot, and a replacement connector pigtail is the lasting repair.
- Swap injector 3 with a neighbour
With fuel pressure relieved, move injector 3 to an adjacent port and put that injector in cylinder 3. Clear the codes and run the engine: if the circuit code follows to the other cylinder, the injector is bad; if it stays on cylinder 3, the wiring or the engine computer is to blame.
- Trace the cylinder 3 control wire to the computer
If the injector proves innocent, use a wiring diagram to check continuity from the injector connector to the matching engine computer pin, and check that wire for a short to ground or to voltage. A clean harness plus a working injector leaves the computer's driver, which is rare and needs a programmed replacement.
DIY or shop? Connector work and the terminal check suit most owners, and swapping injectors on an accessible port-injected rail is a moderate job — relieve pressure, keep dirt out of the open ports, and use fresh O-rings. It shifts to the shop if the middle injectors sit beneath an intake you'd have to remove, if the engine is direct-injected, or if the diagnosis ends at the engine computer, which needs programming to the vehicle.
Tools for the DIY steps: Inspection mirror and flashlight · Terminal test pins · Digital multimeter · Fuel injector O-ring kit · Wiring diagram for your engine
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0203.
Start a case with P0203 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0203?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0203: common questions
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?
Redline can't make that call from the code alone. A dead cylinder feeds raw fuel to the catalytic converter with every mile, and converter damage costs far more than the injector-circuit fix, so get it repaired promptly. 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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0203 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0203 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.