P0203: The fuel injector circuit for cylinder 3 has a fault
Injector Circuit Malfunction -- Cylinder 3
There is a fault in the cylinder 3 fuel injector circuit, which causes a misfire. Get it checked today. If the light is flashing, stop driving and have it towed.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0203 means the PCM detected an electrical fault in the fuel injector circuit for cylinder 3. The PCM measures current flow when it fires each injector. If the return signal is missing or wrong, it sets this code. A related cylinder 3 misfire code (P0303) is almost always stored at the same time. This is a circuit electrical fault, meaning the problem may be the injector itself, the wiring, or the connector rather than a clogging or fuel delivery issue.
Common causes
- Damaged wiring between PCM and cylinder 3 injectorChafing against the block, heat shield, or other components breaks the circuit.
- Failed cylinder 3 injector coilMeasure the injector resistance. Out-of-spec reading confirms a bad solenoid.
- Corroded cylinder 3 injector connectorPins oxidized from heat and humidity break the signal path without visibly damaging the injector.
- PCM driver failure for cylinder 3Last resort diagnosis. Only consider after wiring and injector checks come back normal.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Wiring or connector repair
- Fuel injector replacement (single)
- PCM diagnosis and replacement
Symptoms
- Check engine light on, steady or flashing
- Rough idle and vibration
- Power loss under acceleration
- P0303 misfire code likely also stored
- Fuel economy reduction
What to do next
Use a multimeter to measure injector resistance at the harness connector. Compare the reading against the spec for your vehicle. If it is out of range, the injector is faulty. If it reads normal, the fault is in the wiring between the injector and the PCM. Trace the harness carefully, looking for melted insulation or a pinched wire near engine mounts.
Lewis reads P0203 alongside any misfire codes for cylinder 3, so you can confirm the injector fault is causing a misfire before disconnecting anything. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Does a circuit code mean the injector is clogged?
- No. P0203 is about the electrical circuit, not fuel flow. A clogged injector that still has correct resistance would not set this code.
- What is the correct resistance for a fuel injector?
- Port injectors typically measure 10 to 18 ohms. Direct injection injectors are usually 1 to 5 ohms. Always check the spec for your specific engine.
- Will the car run if I just clear this code?
- The code will return almost immediately. Clearing it without fixing the fault only delays the repair and risks catalytic converter damage from the ongoing misfire.
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