P0204 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts running very rough, stalls, or the check-engine light begins flashing.
!You smell raw fuel or the injector fault is paired with a severe drivability change.

If the light is steady and the vehicle still drives normally: Sometimes yes for a short time, but rough running or a flashing light should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Confirm the cylinder numbering for the engine before testing the injector
2
Free - no tools
Inspect the cylinder 4 injector connector and harness for corrosion, looseness, heat damage, or anything recently disturbed
3
Basic tool needed
Check whether P0204 appears with a cylinder 4 misfire or fuel-trim code
4
Basic tool needed
If scan data is available, compare the injector command with the way the engine actually behaves
5
Basic tool needed
Verify that prior service work did not leave the injector harness pinched or partially unplugged

If the code returns

-If the circuit checks out but the code stays on cylinder 4, the injector itself becomes more likely.
-If moving the harness changes the fault, the wiring path deserves another look before replacing parts.
-If the code returns after repair, confirm the cylinder mapping and command side before going deeper.

Background

What this code means

P0204 is a generic OBD-II injector circuit code.

Cylinder 4 is the focus, but the first checks still start with the connector, wiring path, and injector command behavior.

A cylinder 4 misfire, rough running at idle, or a cylinder-specific fuel imbalance can fit this code.

Diagnosis

Common causes

Most common

Cylinder 4 injector wiring fault

A poor connector or damaged wire can interrupt injector control.

Common

Failed cylinder 4 injector

The injector may not open or close correctly when commanded.

Common

Injector driver issue

The control side may not be driving the injector properly.

Possible

Related misfire or mixture issue

A broader engine fault can show up as a circuit code on this cylinder.

Avoid these mistakes

What not to do

xDo not replace the injector first if the real problem is wiring, connector damage, or a control-side fault.
xDo not keep driving if the engine starts misfiring badly, stalling, or running much rougher than before.

Parts

Parts that may need replacing

PartTypical costNotes

Cylinder 4 fuel injector$60-$250Relevant when testing points to the injector itself.

Injector connector pigtail$15-$90Worth checking if the plug is loose, corroded, or heat damaged.

Injector harness repair$20-$150Often the right fix when the wiring path is the real fault.

Related OBD codes

P0200

P0200 usually means the injector circuit has a general malfunction.

P0304

P0304 usually means cylinder 4 is misfiring.

P0171

P0171 usually means bank 1 is running too lean.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0204 was seeded from the dtcdb generic reference list and then expanded around cylinder 4 injector circuit faults, including connector, wiring, and injector problems.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0204 - P0204 Usually Means the Injector Circuit Has a Malfunction on Cylinder 4