P0203 OBD2 Code Guide
P0203 is a powertrain diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Injector Circuit Malfunction - Cylinder 3
Code P0203 indicates that the Powertrain Control Module (PCM) has detected an electrical malfunction within the fuel injector circuit specifically for cylinder #3. This means the PCM observed an unexpected resistance, an open circuit, a short circuit, or an incorrect voltage reading in the wiring or the injector coil itself, preventing proper operation of the injector. This typically results in a misfire condition for cylinder 3, leading to noticeable engine performance issues.
Code verification standard
P0203 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0203 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0203 diagnostic path
- 1Perform a thorough visual inspection of the fuel injector #3 wiring harness and connector for any signs of damage, fraying, corrosion, or loose connections. Also, check for any signs of rodent damage or aftermarket modifications.
- 2With the ignition off, disconnect the injector #3 electrical connector. Use a multimeter to measure the resistance across the injector's terminals. Compare this reading to the manufacturer's specifications (typically 10-18 ohms). An open circuit (OL) or a reading significantly outside the specified range indicates an internal injector fault.
- 3With the ignition ON (engine OFF), use a multimeter to check for battery voltage at one of the injector #3 connector terminals (power feed). Then, with the engine cranking or running, use a noid light or oscilloscope to check for a pulsing ground signal at the other terminal from the PCM. Lack of consistent power or a proper ground pulse indicates a wiring issue or PCM fault.
- 4If the injector resistance and power/ground signals appear correct, consider swapping the #3 injector with an injector from a known good cylinder (e.g., cylinder #1 or #2). Clear the codes and retest. If the code moves to the new cylinder, the injector is faulty. If P0203 persists, the issue is likely wiring or PCM related.
Verify before repair
- - Replace the faulty fuel injector for cylinder #3.
- - Repair or replace damaged wiring or corroded connectors leading to the #3 fuel injector.
- - Replace the Powertrain Control Module (PCM) if all other diagnostic steps confirm it as the root cause (this is less common and should only be considered after ruling out all other possibilities).
Vehicle-specific pages to check next
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