Open or short circuit in the injector coil on cylinder 4; Damaged, chafed or corroded wiring between the injector and the control unit; Loose, corroded or contaminated injector connector or control unit connector pins; Poor power supply or earth to the injector circuit, such as a blown fuse or faulty relay (depends on model); Wiring harness damaged by heat or rubbing near the engine, or by previous repair work; Fault in the injector driver inside the engine control unit.

P0204

Cylinder 4 Injector A Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
04: FaultThe specific fault in that area

What it means

P0204 means the engine control unit has detected a fault in the electrical circuit that operates the fuel injector on cylinder 4. It monitors the injector driver and its wiring, and sets the code when the voltage or current is not what it expects, such as an open circuit, a short or a failed injector coil. This is an electrical circuit fault, not a direct measure of fuel delivery, although fuel delivery to that cylinder is usually affected.

Symptoms

Engine misfire, rough running or shaking at idle
Malfunction indicator lamp on
Loss of power or poor acceleration
Hesitation or stumbling under load
Hard starting or an engine that cranks but runs on fewer cylinders
Raw fuel smell or higher fuel consumption

Possible causes

Open or short circuit in the injector coil on cylinder 4likely
Damaged, chafed or corroded wiring between the injector and the control unitlikely
Loose, corroded or contaminated injector connector or control unit connector pinslikely
Poor power supply or earth to the injector circuit, such as a blown fuse or faulty relay (depends on model)possible
Wiring harness damaged by heat or rubbing near the engine, or by previous repair workpossible
Fault in the injector driver inside the engine control unitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for other injector or misfire codes.
Visually inspect the cylinder 4 injector connector and the nearby wiring for chafing, heat damage, corrosion, bent pins or a loose fit.
Clear the code and see if it returns, and check whether the misfire is confined to cylinder 4 using live misfire counters.
With the connector removed, measure the injector coil resistance and compare it with the manufacturer's specification for that engine.
Check the injector supply voltage and fuse or relay feed, as the layout depends on the model and engine.
Use a test light or injector driver test lamp, or a scope, to confirm the control unit is sending a switching signal to the cylinder 4 injector.
Check the wiring for continuity and for shorts to earth or to voltage between the injector connector and the control unit connector, following the wiring diagram for the vehicle.
If the injector and wiring are good, check the control unit connector and consider a control unit fault only after everything else is ruled out.

How to fix

Replace the cylinder 4 injector if its coil resistance is out of specification or it is open or shorted.
Repair or replace damaged wiring, and secure it so it cannot rub or overheat again.
Clean or replace corroded or damaged connectors and terminals.
Replace any blown fuse or faulty relay in the injector supply, after finding why it failed.
Repair or replace the engine control unit only if it is confirmed as faulty, and follow the manufacturer's procedure for coding or programming it.

Can I keep driving?

Medium severity

The car can be driven a short distance if it runs reasonably, but get it checked soon. A dead injector circuit can cause a persistent misfire and unburnt fuel, which can overheat and damage the catalytic converter, so avoid heavy loads and long journeys.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.