P0203

Code

Generic P — Powertrain

Cylinder 3 Injector A Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 35 EN: 147 RU: 74

AI status

Completed

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Page language: EN

Causes

Faulty cylinder 3 fuel injector
Open or shorted wiring in injector harness to cylinder 3
Corroded, loose, or damaged injector connector or pins
Blown fuse or faulty EFI/main relay (injector supply)
PCM driver output fault
High resistance in connector or wiring (intermittent)

Symptoms

Check Engine Light (MIL) illuminated
Rough idle or misfire at cylinder 3
Reduced engine power and acceleration
Poor fuel economy and increased emissions
Intermittent stalling or hard start (depending on severity)
Fuel odor if injector stuck open/leaking

What to check

Read stored freeze frame and pending codes with scan tool; confirm P0203 and related codes (misfire, fuel trim)
Visually inspect wiring and connector at cylinder 3 injector for damage, corrosion, pin push-out or loose terminal
Verify EFI/fuel injector supply fuse and relay operation
Backprobe injector connector while cranking/idle: check for battery voltage on the supply pin
Measure injector coil resistance with engine off and connector disconnected
Use a noid light or oscilloscope to verify injector drive pulse from PCM while cranking or running

Signal parameters

Injector supply (B+) ~ vehicle battery voltage (approx. 12 V) present at injector supply pin with ignition ON
Injector coil resistance (typical gasoline): high-impedance 10–16 Ω or low-impedance 2–5 Ω depending on design (check OEM spec)
Injector drive: PCM switches the other side to ground (or to voltage for some architectures) with pulse widths commonly 1–8 ms at idle, longer under load
Pulse frequency varies with engine speed and fuel strategy; frequency increases with RPM
Expected waveform: sharp transition when driver switches, repeatable pulse train; no pulse or stuck high/low indicates a fault

Diagnostic algorithm

Confirm code and capture freeze-frame/live data. Note related codes (misfire P0303, fuel trim, supply faults).
Visually inspect connector, wiring, and harness routing for mechanical damage, melted insulation, corrosion, or pin damage. Repair as needed.
With ignition OFF, disconnect injector connector and measure injector coil resistance. Compare to OEM spec. Replace injector if out of range or open/shorted.
With key ON (engine OFF) verify battery voltage at injector supply terminal. If no supply, check relevant fuses and EFI/fuel relay.
Reconnect, start engine or crank and backprobe the injector control terminal. Use a noid light to verify presence of injector pulses. If pulses absent, test PCM driver and wiring continuity.
If pulses present but injector not operating, bench-test or swap injectors with another cylinder to see if problem follows the injector.
Perform continuity and resistance checks between injector connector pin and PCM connector pin to detect opens or shorts to ground/power. Repair harness as required.
Use an oscilloscope to inspect injector drive waveform for proper switching, amplitude and shape (look for shorts, slow edges, intermittent signals).
If wiring and injector test good and PCM control signal abnormal, consider PCM driver fault and consult manufacturer procedures before PCM replacement.
Clear codes and road test to confirm repair. Re-scan for return of P0203.

Likely causes

Broken/shorted harness between injector and PCM
Bad/contaminated cylinder 3 injector
Poor connector contact or corrosion at injector plug
Faulty PCM driver for injector circuit
Failed EFI relay or related supply fuse

Fault status

⚠️ Status

PCM detected a malfunction in the injector circuit for cylinder 3 (Injector A): open, short, high resistance, poor connection, or injector failure. Repair wiring/connector or replace injector/PCM as required after diagnosis.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours