Bad cylinder 3 fuel injector (both sources; OBD-Codes.com says this is usually the cause). Open or short in the wiring to the injector (OBD-Codes.com), or a wiring issue (RepairPal). Bad PCM (both sources). The sources lean differently: OBD-Codes.com points first to the injector, while RepairPal lists the injector, the PCM and wiring without ranking them, and names fuel injector replacement as the common repair.

Repair open or shorted wiring or a damaged connector in the cylinder 3 injector circuit (both sources list wiring). Replace the cylinder 3 fuel injector if it is out of spec or the code follows it (both sources; RepairPal lists injector replacement as the common repair). Repair or replace the PCM only after the injector and wiring test good (both sources list the PCM as a possible cause).

P0203⛽ Fuel injection / Injector circuitStop and fix promptly

P0203: Injector Circuit/Open, Cylinder 3 (Meaning, Causes, Fixes)

Q: What does P0203 mean?

P0203 means the engine computer has found a fault in the electrical circuit for the cylinder 3 fuel injector, or can't control that injector. OBD-Codes.com says a bad injector is usually the cause, but open or shorted wiring or the engine computer itself can also set it. The powertrain control module (PCM) turns each fuel injector on and off using transistors that RepairPal calls drivers. OBD-Codes.com explains that when the injector is switched on the PCM expects the voltage on its control wire to be pulled low, close to zero, and when it is switched off it expects close to battery voltage. If the PCM doesn't see the expected voltage, or the circuit resistance is excessively high or low, it sets P0203. RepairPal puts it more simply: if the PCM cannot control the cylinder 3 fuel injector, it sets P0203. The two sources name it slightly differently: OBD-Codes.com calls it Cylinder 3 Injector Circuit Malfunction and RepairPal calls it Injector Circuit/Open, Cylinder 3, but they describe the same fault. It is a generic OBD-II code, though repair steps vary by make and model. P0201, P0202 and P0204 through P0212 cover the other cylinders, and P0200 is the general injector circuit code. Which cylinder is number 3 depends on the engine, so check your vehicle's firing-order diagram before working on it.

Q: Can I keep driving with P0203?

Stop and fix promptly. Get it diagnosed soon and don't ignore it. RepairPal rates P0203 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com says it will likely cause a misfire, rough running and poor acceleration. If the check engine light is flashing, the engine is shaking badly, or it loses power, keep driving to a minimum and have it checked, since a misfiring cylinder can damage other parts.

Reviewed 2026-10-23 · Based on 2 cited source(s)

What P0203 means

The powertrain control module (PCM) turns each fuel injector on and off using transistors that RepairPal calls drivers. OBD-Codes.com explains that when the injector is switched on the PCM expects the voltage on its control wire to be pulled low, close to zero, and when it is switched off it expects close to battery voltage. If the PCM doesn't see the expected voltage, or the circuit resistance is excessively high or low, it sets P0203. RepairPal puts it more simply: if the PCM cannot control the cylinder 3 fuel injector, it sets P0203. The two sources name it slightly differently: OBD-Codes.com calls it Cylinder 3 Injector Circuit Malfunction and RepairPal calls it Injector Circuit/Open, Cylinder 3, but they describe the same fault. It is a generic OBD-II code, though repair steps vary by make and model. P0201, P0202 and P0204 through P0212 cover the other cylinders, and P0200 is the general injector circuit code. Which cylinder is number 3 depends on the engine, so check your vehicle's firing-order diagram before working on it.

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon and don't ignore it. RepairPal rates P0203 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com says it will likely cause a misfire, rough running and poor acceleration. If the check engine light is flashing, the engine is shaking badly, or it loses power, keep driving to a minimum and have it checked, since a misfiring cylinder can damage other parts.

Common symptoms

Check engine light on (OBD-Codes.com)
Misfire and rough running (OBD-Codes.com)
Poor acceleration (OBD-Codes.com), or decreased engine performance (RepairPal)
Increased fuel consumption (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Bad cylinder 3 fuel injector (both sources; OBD-Codes.com says this is usually the cause)
Open or short in the wiring to the injector (OBD-Codes.com), or a wiring issue (RepairPal)
Bad PCM (both sources)
The sources lean differently: OBD-Codes.com points first to the injector, while RepairPal lists the injector, the PCM and wiring without ranking them, and names fuel injector replacement as the common repair

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. Misfire codes such as P0303 or P0300 often appear alongside P0203, and several injector codes at once point toward shared wiring or power rather than one injector.
Visually check the cylinder 3 injector, its connector and wiring for damage or broken wires (OBD-Codes.com).
With a digital multimeter, check the injector's resistance against your vehicle's spec and replace it if it's out of spec, and check for 10 volts or more at the injector connector (OBD-Codes.com).
If you have an injector tester, activate the injector and see whether it operates; if it does, OBD-Codes.com says you likely have an open in the wiring or a blocked injector. Without a tester, swap the injector with another cylinder's and see whether the code changes, for example to P0202 or P0204. If it moves, replace the injector.
Avoid grounding PCM wires unless you are certain you have the correct wire; OBD-Codes.com warns not to attempt it if you're unsure.

Typical fixes

Repair open or shorted wiring or a damaged connector in the cylinder 3 injector circuit (both sources list wiring)
Replace the cylinder 3 fuel injector if it is out of spec or the code follows it (both sources; RepairPal lists injector replacement as the common repair)
Repair or replace the PCM only after the injector and wiring test good (both sources list the PCM as a possible cause)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The check engine light is flashing or the engine runs very rough
Confirming the circuit needs an injector tester, harness continuity tests, or work on the PCM driver wire, which OBD-Codes.com says not to attempt if you're unsure of the wire
The injector and wiring test good and the code returns, which can point to the PCM
Several injector codes appear at once, which suggests a shared power feed or wiring problem rather than one injector

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0203 serious?

Treat it as serious. RepairPal rates it Urgent, and OBD-Codes.com says it will likely cause a misfire and rough running. Get it diagnosed soon.

Is P0203 always a bad injector?

No. OBD-Codes.com says the injector is usually the cause, but both sources also list wiring problems and the PCM. Test before buying parts.

Will new spark plugs fix P0203?

Not on their own. Neither source lists spark plugs as a cause; P0203 is about the injector's electrical circuit, so test the injector and its wiring first.

How much does it cost to fix P0203?

Neither source gives a repair cost. The price depends on whether it's wiring, the injector, or the PCM, so get a diagnosis or a written estimate before replacing parts.

Sources

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.