Code
P1203
JAGUAR
P — Powertrain
Cylinder 3 Injector Circuit Open/Shorted
AI status
Completed
Completed
100%
Causes
- Broken or damaged wiring in the injector harness to cylinder 3
- Corroded, loose, or pushed-out connector at the injector or ECM
- Open injector (internal coil failure)
- Injector shorted to ground or battery (internal or wiring)
- Blown fuse or faulty power/relay supplying injector rail
- Poor or missing ground connection for injector circuit or engine harness
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Rough idle or engine misfire localized to cylinder 3
- Reduced engine power, hesitation or poor acceleration
- Decreased fuel economy
- Possible misfire code for cylinder 3 (e.g., P0303) logged alongside P1203
- Engine may run rough only under certain conditions or not start if circuit is open
What to check
- Read and record trouble codes and freeze frame data with a scan tool. Note any related misfire or injector codes.
- Visual inspection of injector 3 connector, wiring harness, and routing for chafing, heat damage, or corrosion.
- Check injector power supply (fuse and injector supply relay) and common injector rail voltage at connector.
- Verify engine and chassis grounds in the area of the injector rail.
- Measure injector coil resistance at the connector (reference service manual spec).
- Check continuity between injector pin and ECM driver pin; inspect for short to ground or battery.
Signal parameters
- Injector supply: battery voltage present on the injector positive feed with ignition ON (verify per model).
- Injector driver: pulsed ground or voltage from the ECM when the engine is cranking/running — pulses visible with a noid light or oscilloscope.
- Pulse width: typically in the range of ~1–10 ms depending on load and RPM (varies by engine and operating condition).
- Injector coil resistance: varies by injector design — commonly low-impedance injectors are a few ohms, high-impedance types ~10–16 Ω; compare measured value to factory spec.
- Continuity: low resistance continuity between injector connector and ECM driver pin; no short to battery or ground between them.
Diagnostic algorithm
- Retrieve codes and freeze frame, note related codes (P0303, P0203, etc.).
- Visually inspect injector 3 connector and wiring for damage, corrosion, rodent chewing, or loose pins. Repair as needed.
- Verify injector supply power (key ON) at the injector harness connector. Check fuse and relay feeding the injector rail.
- With ignition OFF, measure injector coil resistance at the connector and compare to factory spec. If open or shorted, replace injector.
- Check continuity between the injector terminal and the ECM injector driver pin with harness disconnected. Look for opens or high resistance.
- Check for short to ground or battery on the driver circuit using an ohmmeter and by isolating the harness from the ECM. Repair wiring as required.
- Backprobe the injector connector while cranking/running with a noid light or oscilloscope to confirm the ECM is commanding the injector and that pulses are present and within expected shape.
- Perform a wiggle test of the harness/connectors while monitoring live data to catch intermittent faults.
- Swap injector 3 with another cylinder’s injector (if identical and permitted) to determine if the fault follows the injector or stays on cylinder 3 — if it follows the injector, replace the injector.
- If wiring and injector are good, test or replace ECM driver circuit per factory procedures (replace ECM only after confirming driver fault and after verifying grounds/power).
- Clear codes and road test to confirm repair. Re-scan to ensure no reoccurrence.
Likely causes
- Damaged / corroded connector or wiring in harness to injector 3
- Failed injector (open coil or internal short)
- Faulty power supply (fuse or relay) or poor ground
- ECM driver fault (less common than wiring/injector issues)
Fault status
Status
Detected open or short in fuel injector circuit for cylinder 3. ECM has identified abnormal electrical condition preventing proper injector operation.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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