Drivable briefly and gently, but a persistent cylinder-3 misfire pushes raw fuel into the exhaust and can overheat the catalytic converter — fix it soon to avoid a costly cascade. P0203 is a powertrain code meaning the engine computer has detected an electrical fault — an open or a short — in the fuel-injector control circuit for cylinder 3 only. It points at the number-three injector's coil, its wiring and connector, or the injector driver inside the PCM, not at fuel quality or spray pattern.
What P0203 means
A fuel injector is an electrically operated valve: the powertrain control module (PCM/ECM) fires it by switching the low side of its circuit to ground while battery voltage (VPWR) feeds the high side, so current pulses through the injector coil for a few milliseconds each engine cycle. A self-check — Ford calls it the comprehensive component monitor (CCM) — watches the injector driver for cylinder 3 and expects to see the coil's electrical load every time it commands that injector. If that load is missing or the current is out of range because the circuit is open, shorted to ground, or shorted to power, the monitor fails and stores P0203. The code is specific to cylinder 3; the same fault on its neighbors sets P0201 (cylinder 1), P0202 (cylinder 2), and P0204 (cylinder 4), while P0200 is the umbrella "injector circuit" code used when the fault cannot be tied to one cylinder. Because P0203 is electrical, it implicates the cylinder-3 injector solenoid, its connector and harness, or the low-side driver inside the module — not fuel pressure. On many vehicles the test runs continuously, key-on and while running, and can set from a single detected open.
Symptoms
- Cylinder-3 misfire that a scan tool logs as a rising misfire counter on that specific cylinder, often alongside companion code P0303
- Rough, shaking, or loping idle that smooths only slightly as engine speed climbs
- Hard starting or extended cranking, most noticeable when the engine is cold
- Noticeable hesitation, stumble, or loss of power under acceleration
- Check-engine light on — sometimes flashing during an active misfire — occasionally with a raw-fuel or sulfur smell from the exhaust and worse fuel economy
Common causes
- Open or failed cylinder-3 injector solenoid coil (internal winding break) — the most common single cause
- Damaged wiring or a loose, backed-out, or corroded connector at the number-three injector
- Chafed or broken injector harness rubbing against the engine, a bracket, or the intake near cylinder 3
- Corrosion or water intrusion in the cylinder-3 injector connector pins raising circuit resistance
- Open VPWR feed to the injector, or an INJ3 control wire shorted to ground or to power (short-to-ground and short-to-voltage apply mainly to direct-injection engines)
- Failed low-side injector driver for cylinder 3 inside the PCM/ECM (least common, confirmed last)
Severity & driving advice
Severity: Moderate — A dead cylinder-3 injector causes a steady misfire; prolonged driving dumps raw fuel that can overheat and ruin the catalytic converter.
Can I drive? Drivable briefly and gently, but a persistent cylinder-3 misfire pushes raw fuel into the exhaust and can overheat the catalytic converter — fix it soon to avoid a costly cascade.
Diagnostic approach
- Confirm the code and isolate cylinder 3 — Read all stored codes and note whether P0203 appears with a matching cylinder-3 misfire code (P0303) or with other injector-circuit codes such as P0202 or P0204. On Ford the INJ3_F PID flags cylinder 3 in live data (it equals YES on port-injected engines, or flags a concern on direct-injection engines). Check the monitor status and freeze-frame so you know whether the fault is currently present or intermittent before probing anything.
- Inspect the cylinder-3 injector connector and harness — Unplug the number-three injector and inspect the connector for spread, corroded, or pushed-out pins and for moisture. Follow the injector harness for chafe points and broken insulation where it passes brackets or the intake. Reseat the connector and perform a wiggle test with the ignition on, watching a live scan-tool data line for the fault dropping in and out — a strong sign of an intermittent wiring fault rather than a dead injector.
- Measure injector coil resistance — With the connector off, measure resistance across the two injector terminals. A healthy high-impedance (saturated) port injector typically reads roughly 11-16 Ω at room temperature — confirm the exact figure against the engine's own specification. An infinite / OL reading means an open coil (a definite failure), while a near-zero reading indicates a shorted winding. Compare directly against a known-good injector on the same engine.
- Test the circuit back to the module — Key on, confirm battery voltage on the VPWR feed side of the cylinder-3 injector connector. Check continuity of the INJ3 control (low-side) wire from the injector connector back to the correct PCM pin, and test that wire for a short to ground and a short to power. On direct-injection engines also verify the injector-return (INJ3RTN) circuit for opens and shorts. Repair any open, high-resistance, or shorted section before condemning the injector or the module.
- Verify the injector pulse and driver — With good wiring, back-probe for the cylinder-3 injector pulse using a noid light or scope while cranking. No pulse on a confirmed-good circuit points to the low-side driver inside the PCM — Ford routes port-injected engines to Pinpoint Test KG and direct-injection engines to Pinpoint Test DI for this. Confirm the injector fuse/relay and shared VPWR feed are good so you don't blame the module for an upstream supply fault.
- Swap the injector to confirm the fault — As a final cross-check, swap the cylinder-3 injector with an adjacent cylinder's injector and clear the codes. If the fault (and any misfire) follows the injector to the new cylinder, replace the injector; if P0203 stays on cylinder 3, the wiring or the PCM driver is at fault. This isolates the failure without guessing.
Make & model notes
Ford: Ford groups P0201-P0208 as Injector Circuit/Open for cylinders 1-8, with the comprehensive component monitor watching each injector driver in the PCM; the INJ3_F PID flags cylinder 3. On port-injected engines such as the 5.0L Coyote F-150 the factory routes diagnosis to Pinpoint Test KG, which checks the VPWR feed and the INJ3 control wire; direct-injection GTDI/EcoBoost engines use Pinpoint Test DI, which also checks the injector-return (INJ3RTN) circuit for opens and shorts. Verified against 2014 F-150 5.0L factory data.
Jeep / Chrysler: On Stellantis Pentastar 3.6L engines (Grand Cherokee, 300, Charger), P0203 is the cylinder-3 injector circuit; the PCM switches the injector's ground side while an ASD-relay-fed +12V supplies the coil. Inspect the number-three injector connector and its +12V feed, confirm the injector coil resistance against the per-engine value, and check the control wire back to the PCM before replacing the injector or suspecting the module.
FAQ
What does the P0203 code mean?
P0203 means the engine computer has found an electrical problem — an open circuit or a short — in the control circuit for the cylinder-3 fuel injector. Each injector is a small electromagnet the computer switches on and off, and P0203 sets when the self-check for cylinder 3 no longer sees the expected electrical load. It is a wiring and injector-coil fault, not a fuel-quality or spray issue.
Can I drive with a P0203 code?
Only briefly, and gently. If cylinder 3 has stopped firing you will feel a misfire, and the unburned fuel pushed into the exhaust can overheat and permanently damage the catalytic converter — an expensive part. The engine is also down on power and running rich. Get the injector circuit repaired promptly rather than driving on a persistent misfire.
What is the difference between P0203 and P0303?
P0203 is an electrical fault in the cylinder-3 injector control circuit — an open or short the computer sees on the injector driver. P0303 is a cylinder-3 misfire the computer detects from crankshaft speed. They often appear together because a dead injector circuit makes cylinder 3 stop firing, but P0203 tells you the root cause is electrical, so test the injector coil and its wiring first.
How is P0203 different from P0202 and P0204?
They are the same fault on different cylinders: P0202 is the cylinder-2 injector circuit, P0203 is cylinder 3, and P0204 is cylinder 4. The diagnosis is identical — inspect that injector's connector and harness, measure its coil resistance, and test the control wire back to the PCM — you just work on the injector for the cylinder the code names. P0200 is used when the fault can't be tied to one specific cylinder.
What usually fixes a P0203 code?
Most often the fix is the cylinder-3 injector itself when its coil has gone open, or a repair to its connector or wiring when a pin is corroded, backed out, or the harness has chafed. Measuring the injector's resistance and checking the INJ3 circuit back to the computer tells you which. A failed driver inside the PCM is possible but uncommon, so it is confirmed last, after the injector and wiring test good.