P0203 — Fuel injector failure, Powertrain Control Module (PCM) failure, Wiring issue

Causes

• Open or shorted injector wiring harness to injector 3
• Corroded, loose or damaged injector connector/pin
• Failed fuel injector (internal open or short)
• Faulty PCM/injector driver
• Blown fuse or relay affecting injector power/PCM
• Intermittent wiring damage (chafing, rodent, heat)

Symptoms

• Check Engine Light (MIL) illuminated
• Rough idle or vibration, especially at idle
• Misfire detected on cylinder 3 (P0303 may also set)
• Loss of power, hesitation on acceleration
• Poor fuel economy and increased emissions
• Possible hard starting or no-start if severe

What to check

• Retrieve freeze frame and live data with a scan tool; note cylinder 3 misfire, fuel trim, and injector status
• Visually inspect wiring, connectors, and harness for damage, corrosion, or pin push-out at injector 3
• Check battery voltage and relevant fuses/relays for proper operation
• Measure injector 3 resistance at the connector (unplugged) and compare to manufacturer spec
• Back-probe injector connector with oscilloscope or DVOM (for pulse presence and voltage levels) while cranking/running
• Wiggle test wiring while monitoring for changes or intermittent faults

Signal parameters

• Injector coil resistance: typically ~2–16 ohms depending on high- or low-impedance design — consult Audi spec
• Resting circuit voltage at injector power feed: battery voltage (approx. 12–14 V with key on/engine running)
• Injector driver ground switching: PCM pulls injector low to energize; expect ~0 V on switched side when energized
• Injector pulse width: varies with load; small at idle (~1–3 ms) and longer under load; observable with scope
• No short to battery: no sustained 12 V on driver side when injector should be open

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