P1203

Code

Other P — Powertrain

Injector Circuit Open / Shorted - Cylinder #3

Brand: Other

Type: P — Powertrain

Views: UK: 34 EN: 56 RU: 35

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Page language: EN

Causes

Open circuit in injector harness (broken wire, corroded connector pin)
Short to ground or short to battery in the injector wiring
Faulty fuel injector (internal open, short, or coil failure)
Poor or corroded connector pin/contact at injector
Faulty engine control module (driver transistor) or poor ECU ground
Aftermarket wiring or recent repairs introduced damage

Symptoms

Check Engine Light (MIL) illuminated
Rough idle or misfire felt on cylinder #3
Reduced engine power and hesitation under load
Possible hard start or increased fuel consumption
Engine may run on fewer cylinders; vibration localized to cylinder #3

What to check

Read freeze frame data and live PID for injector pulse and misfire info
Visually inspect injector connector and wiring for damage, heat, corrosion
Backprobe injector connector to check supply voltage and driver signal
Measure injector coil resistance at the connector (compare to spec)
Use noid light or oscilloscope to verify injector drive pulse when cranking/with engine running
Check for continuity to ECM and for shorts to ground/battery

Signal parameters

Injector coil resistance: varies by vehicle; typical ranges: low-impedance 2–5 Ω, high-impedance 10–18 Ω (consult vehicle spec)
Supply voltage at injector harness B+ terminal: ~12 V (battery voltage) with ignition ON
Driver output: pulls injector terminal toward ground when commanded (0–1 V during pulse), floats to B+ when not driven
Injector pulse width: typically 1–15 ms depending on load and RPM (varies by engine)
Injector current during pulse: typically up to a few amps (depends on injector type — verify spec)
Oscilloscope waveform: clean rectangular pulses; glitches, stuck high/low, or no pulses indicate wiring/driver issues

Diagnostic algorithm

Retrieve freeze-frame and confirm P1203 is current/historic. Note conditions (RPM, temp).
Inspect wiring and connector at cylinder #3 injector for corrosion, pins pushed out, melted insulation, or damage.
With ignition OFF, disconnect injector connector and measure coil resistance across injector terminals. Compare to spec. Replace injector if out-of-spec (open or shorted).
With ignition ON (engine off), verify B+ supply at the injector supply terminal. If B+ missing, trace supply fuse/relay and wiring.
Backprobe the injector driver terminal while cranking or running. Use a noid light or oscilloscope to confirm injector drive pulse. No pulse suggests ECU driver or wiring open; constant voltage suggests short/driver stuck.
Check continuity between the injector driver pin and the ECM connector; check for shorts to ground and to battery. Repair any harness faults found.
Swap the suspected injector with a known-good injector from another cylinder (if practical). Clear codes and run engine; if code follows injector, replace injector. If code stays on cylinder #3, suspect wiring or ECU driver.
If wiring and injector check OK, test ECU driver output and ECU grounds. Replace or repair ECU only after confirming driver failure with proper bench/vehicle-level tests.
After repairs, clear codes and road test to verify no recurrence and proper engine operation.

Likely causes

Corroded or loose connector at cylinder #3 injector
Open or damaged wiring between injector and ECM (pinched, chafed)
Failed injector coil (open or shorted)
Short to ground from wiring harness abrasion near engine or firewall

Fault status

⚠️ Status

Injector circuit open/short detected on cylinder 3. ECM reports abnormal electrical behavior (open, short to ground, or short to battery) in injector circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours