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DTC codes / Jaguar codes / P1203

P1203 · JaguarCylinder 3 Injector Circuit Open/Shorted

P1203 on a Jaguar means the engine control module (ECM) has detected an open circuit or a short to ground or power in the electrical path for cylinder 3's fuel injector. The ECM commands the injector to fire but sees an unexpected voltage on the control circuit, so it flags the fault and may disable that injector to protect the driver circuitry.

SystemPowertrain
Code typeJaguar specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough idle or misfire that is most pronounced at idle and low engine speeds
  • Noticeable loss of power and sluggish acceleration under load
  • Shaking or vibration from the engine bay, especially when cold
  • A faint fuel smell from the exhaust if the injector is stuck open or not firing
  • In rare cases, the engine may enter limp mode or stall when coming to a stop

Common causes, most likely first

  1. Damaged or chafed injector wiring harness near the cylinder 3 injector connector
  2. Corroded, loose, or water-infiltrated electrical connector at the cylinder 3 injector
  3. Failed cylinder 3 fuel injector with an open internal coil
  4. Short to ground or short to power in the injector control circuit between the ECM and the injector
  5. Faulty engine control module (ECM) driver for cylinder 3 (less common but possible)
  6. Rodent damage or heat-related insulation breakdown on the injector harness

How to diagnose and fix it

  1. Perform a visual inspection of the cylinder 3 injector connector and harness for chafing, corrosion, or loose pins
  2. Disconnect the cylinder 3 injector and measure its resistance with a multimeter; compare to the other injectors
  3. With the injector disconnected, check for battery voltage on the supply side of the connector with the key on
  4. Check the control circuit for a short to ground or short to power using a multimeter and wiring diagram
  5. Perform a wiggle test on the harness while monitoring injector pulse with a noid light or oscilloscope
  6. If wiring and connector are good, swap the cylinder 3 injector with a known-good injector from another cylinder and see if the fault moves
  7. If the fault persists after all electrical checks, test the ECM driver circuit or consult a Jaguar specialist for ECM diagnosis

What a P1203 on a Jaguar really tells you

  • A P1203 does not always mean the injector itself has failed; chafed wiring near the cylinder 3 injector is a very common cause on Jaguars with age-related insulation breakdown.
  • The ECM may disable the cylinder 3 injector when it detects a fault, so the engine can run roughly even if the injector is mechanically fine; always clear the code and retest after repairs.
  • Water intrusion into the injector connector, often from a degraded engine cover seal or cowl drain, can set this code without any visible harness damage until the connector is opened.
  • Swapping the injector to another cylinder is the quickest way to rule out the injector versus the wiring, but the ECM may need a relearn or adaptation reset on some Jaguar models after the swap.
  • A shorted injector can sometimes damage the ECM driver, so ignoring a P1203 for too long may turn a cheap wiring repair into an expensive module replacement.

Can I keep driving with P1203?

You can usually drive the car short distances to a repair shop, but avoid heavy acceleration and long trips because a misfiring cylinder can overheat the catalytic converter and waste fuel. If the engine is shaking badly or the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Jaguar vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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