P0204 - Cylinder 4 - Injector Circuit Malfunction
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
The P0204 code indicates that the Engine Control Module (ECM) has detected a malfunction in the fuel injector control circuit for cylinder number 4. The ECM monitors the injector circuit for specific voltage and resistance parameters. When the ECM grounds the injector to open it, it monitors the pulse width and current flow. If the circuit does not meet the calibrated values (e.g., due to an open circuit, high resistance, or a short to ground/voltage), the ECM flags this code. This often triggers a limp home mode or cylinder deactivation to prevent catalyst damage due to misfires.
Possible Causes
Faulty fuel injector for cylinder 4 (internal electrical failure)
Wiring harness issues (chafed wires, corrosion, or broken circuit)
Poor connection or bent pins in the injector connector
Internal Engine Control Unit (ECU) failure
Symptoms
Recommended Solution
- Visual Inspection: Check the injector connector and wiring harness for cylinder 4 for signs of damage, heat stress, or corrosion.
- Resistance Test: Unplug the injector and measure resistance across the terminals using a multimeter. Typical values are 12-16 Ohms for high-impedance injectors. Compare with neighboring injectors.
- Voltage Check: Verify battery voltage (approx. 12V) at the supply wire of the connector with the ignition on.
- Signal Test: Use a Noid light or oscilloscope to verify that the ECU is pulsing the ground side of the circuit while the engine is cranking/running.
- Action: Replace the fuel injector if resistance is out of spec. If wiring is damaged, repair the harness. Clear codes and perform a road test.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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