P0203: Injector Circuit/Open - Cylinder 3

Quick answer

• What this code means: The Powertrain Control Module (PCM) has detected an electrical fault in the fuel injector circuit for cylinder 3.
• Severity: Get towed or address immediately. Prolonged driving can cause significant engine damage.
• Most common cause: A failed fuel injector or a wiring issue in the injector circuit.

What the P0203 code means

The official OBD-II definition for P0203 is "Injector Circuit/Open - Cylinder 3." In simpler terms, this means that the vehicle's computer (PCM) is not seeing the expected electrical signal from the fuel injector responsible for cylinder 3. An "open" circuit indicates a break or lack of continuity in the electrical path, meaning current cannot flow properly to operate the injector. This prevents the injector from delivering fuel to the cylinder, leading to a misfire and a noticeable reduction in engine performance.

Common symptoms

• Check Engine Light illuminated
• Engine misfires, rough idle, or hesitation
• Reduced engine power and acceleration
• Poor fuel economy
• Engine stalling
• Strong fuel smell from the exhaust (due to unburnt fuel from other cylinders attempting to compensate, or raw fuel entering the exhaust if the injector is stuck open or leaking)

Common causes

1. Faulty fuel injector (most common): The injector itself may have an internal electrical fault, such as a broken coil winding, preventing it from opening and closing properly.
2. Wiring harness issues: Damaged, corroded, or shorted wiring in the injector circuit for cylinder 3. This could be due to rodent damage, chafing against engine components, or improper repairs.
3. Bad connection at the injector: A loose, corroded, or damaged connector at the cylinder 3 fuel injector.
4. Faulty Powertrain Control Module (PCM): While less common, an internal fault within the PCM could be incorrectly reporting an issue or failing to send the proper signal to the injector.

How a technician diagnoses it

1. Verify the code and check for other codes: The technician will use an OBD-II scanner to confirm the P0203 code and check for any other related diagnostic trouble codes that might provide additional clues.
2. Inspect wiring and connectors: Visually inspect the wiring harness leading to the cylinder 3 fuel injector for any signs of damage, fraying, corrosion, or pinching. They will also check the injector connector for a secure fit and any signs of corrosion or damage.
3. Perform an injector resistance test: Using a multimeter, the technician will measure the electrical resistance of the fuel injector. A typical good reading for an injector is between 10-18 ohms. A reading significantly outside this range (e.g., infinite resistance for an open circuit, or very low resistance for a short) indicates a faulty injector.
4. Check for power and ground at the injector connector: With the ignition on, the technician will use a multimeter or test light to verify that the injector connector has proper power and ground signals when commanded by the PCM. A good injector circuit should show a constant battery voltage signal on one wire and a pulsed ground signal from the PCM on the other wire during engine cranking or running.
5. Use a noid light: A noid light is a specialized test light that plugs into the injector connector. When the engine is cranked or running, the noid light should flash, indicating that the PCM is sending a pulsed ground signal to the injector. If it doesn't flash, the problem lies upstream in the wiring or the PCM.
6. Swap injector (for diagnostic purposes): If the initial tests are inconclusive, a technician might swap the cylinder 3 injector with a known good injector from another cylinder. If the P0203 code moves to the new cylinder, the original injector is confirmed faulty. If the code remains on cylinder 3, the issue is likely wiring or PCM related.
7. Check PCM drivers (advanced): In rare cases, if all other tests pass, the technician may need to test the PCM's internal injector driver circuit using an oscilloscope to ensure it's properly switching the ground signal.

Typical repair cost

The cost to repair a P0203 code can vary widely based on the cause and your vehicle's make and model. These are general ranges:

• Fuel injector replacement: Parts generally cost $60 - $200 per injector, and labor can be $100 - $300, depending on engine access. Total: $160 - $500.
• Wiring harness repair: This can range from $50 - $250 if only a simple repair (e.g., splicing a wire) is needed. If a significant section of the harness needs replacement, it could be $300 - $800+ for parts and labor.
• Connector replacement: $20 - $80 for the part, plus $40 - $120 for labor.
• PCM replacement: This is the most expensive, with parts costing $500 - $1,500 and labor ranging from $100 - $400, plus potential programming costs of $100 - $300. Total: $700 - $2,200.

Can I keep driving with this code?

No, it is highly recommended to address a P0203 code immediately. Driving with an open fuel injector circuit can lead to severe engine damage. When one cylinder isn't firing, the engine will run rough, and the unburnt fuel from that cylinder can wash away the oil film from the cylinder walls, leading to increased wear. More critically, unburnt fuel entering the exhaust system can rapidly overheat and damage the catalytic converter, which is a very expensive repair. Get your vehicle to a trusted technician as soon as possible.

Related codes

• P0201: Injector Circuit/Open - Cylinder 1
• P0202: Injector Circuit/Open - Cylinder 2
• P0204: Injector Circuit/Open - Cylinder 4
• P0303: Cylinder 3 Misfire Detected
• P0300: Random/Multiple Cylinder Misfire Detected

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