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DTC codes / Volkswagen codes / P1203

P1203 · VolkswagenCylinder 3 Fuel Injector Circuit Electrical Malfunction

P1203 on a Volkswagen means the engine control module (ECM) has detected an electrical fault in the circuit that operates the fuel injector for cylinder 3. The ECM monitors the injector driver circuit for abnormal current flow, such as an open circuit, short to ground, or short to power, and sets this code when the expected electrical signature is not present.

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

Symptoms you may notice

  • Check engine light illuminated, often with no other noticeable symptoms
  • Rough idle or misfire felt as a shake or stumble, especially when cold
  • Loss of power or hesitation during acceleration
  • Increased fuel consumption due to a misfiring cylinder
  • In some cases, the engine may enter limp mode or run poorly under load

Common causes, most likely first

  1. Faulty fuel injector for cylinder 3 (open or shorted internal coil)
  2. Damaged or corroded wiring harness connector at the cylinder 3 injector
  3. Broken or chafed wire in the injector circuit between the ECM and the injector
  4. Failed engine control module (ECM) injector driver for cylinder 3
  5. Poor electrical connection at the ECM connector
  6. Aftermarket or incorrectly installed injector with wrong resistance

How to diagnose and fix it

  1. Perform a visual inspection of the cylinder 3 injector connector and wiring for damage or corrosion
  2. Measure the resistance of the cylinder 3 injector with a multimeter and compare to specification
  3. Check for continuity and shorts in the injector circuit from the ECM to the injector
  4. Swap the cylinder 3 injector with a known-good injector from another cylinder to see if the code moves
  5. Inspect the ECM connector pins for corrosion or looseness
  6. If the circuit and injector test good, test the ECM driver output with an oscilloscope or substitute a known-good ECM
  7. Replace the faulty injector or repair the wiring as needed, then clear the code and verify the repair

Don't overlook the injector connector

  • A loose or corroded connector at the cylinder 3 injector is a common cause that is often missed because the injector itself tests fine.
  • The code can be set by a shorted injector coil that only fails when hot, so testing the injector cold may not reveal the fault.
  • Volkswagen's ECM injector drivers can fail due to heat or age, but this is less common than wiring issues and should be diagnosed last.
  • A misfire from a bad injector can cause unburned fuel to enter the exhaust, which may damage the catalytic converter over time if left unrepaired.
  • Some scan tools may show this code as pending or history; always check freeze-frame data to see the conditions when the fault occurred.

Can I keep driving with P1203?

You can drive the vehicle short distances to a repair shop, but avoid heavy acceleration or long trips because continued misfiring can damage the catalytic converter and reduce fuel economy. If the engine runs very rough or flashes the check engine light, stop driving and seek immediate repair.

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 Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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