P0203 - Injector Circuit Malfunction (Cylinder 3)
P0203 means the injector circuit for cylinder 3 is malfunctioning. The injector may have failed, but damaged wiring, poor connector terminal fit, an open or short in the control circuit, or a PCM driver issue in rarer cases can set the same code.
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Common Next Steps
Turn the code into the next check.
Check coil boots, carbon tracking, and whether the miss follows a swap.
Inspect gap, fouling, wear, oil, coolant, and plug-well condition.
Move to injector balance, pulse, or leak-down checks if the misfire stays.
Use compression or leak-down testing when spark and fuel checks do not move the fault.
Code Overview
P0203 means the injector circuit for cylinder 3 is malfunctioning. The injector may have failed, but damaged wiring, poor connector terminal fit, an open or short in the control circuit, or a PCM driver issue in rarer cases can set the same code.
Common Causes
- Injector connector loose, corroded, oil soaked, or terminal tension poor
- Open, shorted, or high-resistance injector control or power circuit
- Injector coil resistance out of range or injector mechanically stuck
- PCM driver fault after circuit, power, ground, and injector checks pass
- Harness damage from heat, vibration, rodents, or previous engine work
Symptoms
- Rough idle
- Cylinder misfire
- Fuel smell or lean/rich trim shift
- Hard starting
- Reduced power
Diagnostic Steps
- Confirm the affected cylinder and compare with misfire counters and fuel-trim data
- Inspect injector connector fit, terminals, harness routing, and shared power feed
- Use a noid light, scope, or scan data to verify injector command where appropriate
- Measure injector resistance and compare with matching injectors on the same engine
- Check power feed, control-side voltage drop, shorts to power/ground, and continuity before replacing the injector
- Verify repair with smooth idle, no misfire counters, and no pending injector circuit code
Diagnostic Insight
P0203 should be diagnosed as a cylinder 3 injector circuit fault before the injector itself is condemned.
- A circuit code can come from the connector, harness, power feed, or control side, not just the injector.
- If cylinder 3 also misfires, confirm spark and compression so fuel control is not blamed for a different fault.
- Resistance, pulse, and terminal-fit checks usually come before injector replacement.
Repair Difficulty
Moderate
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Next Steps
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