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P0204 Code Explained: Injector Circuit/Open Cylinder 4 Causes, Symptoms & Fixes

P0204 code illustration showing the Cylinder 4 fuel injector, injector wiring harness, PCM, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

If your OBD-II scanner displays P0204, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an electrical fault affecting the fuel injector circuit for Cylinder 4.

The generic OBD-II definition for P0204 is:

Injector Circuit/Open – Cylinder 4

Unlike P0200, which indicates a general injector circuit malfunction, P0204 specifically identifies a problem with the electrical circuit controlling the fuel injector on Cylinder 4.

Modern fuel injection systems rely on the PCM to precisely control each injector individually. The PCM constantly monitors:

If the PCM detects an abnormal voltage or current condition in the Cylinder 4 injector circuit, it stores P0204 and illuminates the Check Engine Light.

Common causes include:

Depending on the severity of the fault, the PCM may disable Cylinder 4’s injector to prevent catalytic converter damage, causing noticeable drivability problems.

What Does the P0204 Code Mean?

The PCM individually controls every fuel injector by rapidly grounding and releasing the injector circuit.

Each injector receives:

If the PCM cannot properly control or monitor the Cylinder 4 injector circuit, it stores P0204.

Unlike fuel delivery problems caused by low fuel pressure or clogged injectors, P0204 specifically indicates an electrical problem affecting the injector circuit.

What Is the Fuel Injector?

The fuel injector is an electrically controlled solenoid valve that sprays a precisely metered amount of fuel into the intake port or directly into the combustion chamber.

Each injector consists of:

When energized by the PCM:

This process occurs thousands of times per minute.

Why Proper Injector Operation Matters

Accurate injector control is critical for:

A malfunctioning Cylinder 4 injector circuit may cause:

Ignoring the problem may eventually damage the catalytic converter.

How the PCM Detects P0204

The PCM continuously monitors:

If the Cylinder 4 injector circuit falls outside manufacturer specifications, the PCM stores P0204.

Most manufacturers require the fault to occur more than once before illuminating the Check Engine Light.

What Does “Injector Circuit/Open” Mean?

An Injector Circuit/Open code means the PCM has detected an interruption or abnormal electrical condition affecting the injector circuit.

Possible causes include:

Additional electrical testing is required to identify the exact cause.

Can Wiring Problems Cause P0204?

Absolutely.

Damaged wiring is one of the most common causes of P0204.

Inspect for:

Heat and engine vibration often damage injector wiring over time.

Can the Fuel Injector Fail?

Yes.

Fuel injectors commonly fail due to:

Electrical injector failures commonly trigger P0204.

Mechanical injector failures may also generate:

Can Low Fuel Pressure Cause P0204?

No.

Low fuel pressure affects fuel delivery but does not create an injector circuit fault.

However, low fuel pressure may also cause:

Fuel pressure should still be verified because multiple faults can occur simultaneously.

P0204 Quick Facts

ItemInformation
DTCP0204
Generic DefinitionInjector Circuit/Open Cylinder 4
SystemFuel Injection / Powertrain
SeverityModerate to High
Safe to Drive?Limited driving only
Common SymptomsCheck Engine Light, Cylinder 4 misfire, rough idle, poor acceleration
Common CausesFailed injector, damaged wiring, loose connector, PCM injector driver
Typical Repair Cost$150–1,500+
Related CodesP0200, P0201, P0202, P0203, P0205–P0212, P0304, P0171, P0172

Common Vehicles That Experience P0204

P0204 commonly appears on:

The code is especially common on:

What Does P0204 Really Mean?

The wording of P0204 often causes drivers to believe the injector itself has failed.

The code does not automatically mean:

Instead, it means the PCM has detected an electrical malfunction affecting the Cylinder 4 injector circuit.

The underlying problem may involve:

Think of P0204 as the PCM saying:

“I’m having trouble communicating with the injector on Cylinder 4. Before replacing the injector, verify the wiring, connector, and control circuit are all working correctly.”

How to Diagnose the P0204 Code

Diagnosing P0204 requires determining why the Powertrain Control Module (PCM) has detected an electrical fault affecting the Cylinder 4 fuel injector circuit.

Unlike P0200, which indicates a general injector circuit malfunction, P0204 specifically identifies a fault within the electrical circuit controlling the fuel injector for Cylinder 4.

The underlying problem may involve:

Because a failed injector circuit can quickly lead to engine misfires, poor fuel economy, catalytic converter damage, and increased emissions, diagnosis should begin as soon as possible.

Safety Precautions

Before beginning diagnosis:

Fuel injectors operate under high fuel pressure, making proper safety procedures essential.

Tools Required

Professional diagnosis may require:

A scan tool capable of monitoring injector pulse width, fuel trims, and misfire counters greatly simplifies diagnosis.

Step 1 – Verify the Code

Connect a professional scan tool.

Record:

Monitor:

Never erase codes before recording freeze-frame information.

Step 2 – Check for Related Trouble Codes

P0204 commonly appears with:

Related injector and fuel system codes often simplify diagnosis.

Code CombinationLikely Diagnosis
P0204 onlyCylinder 4 injector circuit fault
P0204 + P0304Injector causing Cylinder 4 misfire
P0204 + P0171Lean condition caused by poor fuel delivery
P0204 + P0172Injector leaking or driver fault
P0204 + P0200General injector circuit problem

Repair obvious electrical faults before replacing the injector.

Step 3 – Review Freeze-Frame Data

Review:

Freeze-frame data often shows whether the fault occurred during idle, acceleration, or heavy engine load.

Step 4 – Verify Battery Voltage

Before electrical testing:

Measure battery voltage.

Normal values:

Low system voltage can affect injector operation and produce misleading diagnostic results.

Step 5 – Inspect the Cylinder 4 Injector

Locate the Cylinder 4 fuel injector.

Inspect for:

Replace any injector showing obvious physical damage before continuing diagnosis.

Step 6 – Inspect the Injector Wiring Harness

Inspect the wiring leading to the Cylinder 4 injector.

Look for:

Injector wiring located near exhaust manifolds commonly suffers heat-related failures.

Step 7 – Inspect the Injector Connector

Disconnect the Cylinder 4 injector connector.

Inspect for:

Poor connector contact is one of the most common causes of P0204.

Step 8 – Verify Injector Power Supply

With the ignition ON:

Measure battery voltage at the Cylinder 4 injector connector.

If voltage is missing:

Inspect:

Most fuel injectors receive constant battery voltage with PCM-controlled ground switching.

Step 9 – Measure Injector Resistance

Disconnect the injector.

Measure injector coil resistance using a digital multimeter.

Compare the reading with manufacturer specifications.

Replace the injector if resistance indicates:

Step 10 – Verify Injector Pulse

Install a noid light or connect an oscilloscope.

Crank or start the engine.

Verify:

If no injector pulse exists:

Inspect:

Step 11 – Perform Voltage Drop Testing

Measure voltage drop across:

Inspect for:

Even minor resistance can reduce injector performance.

Step 12 – Verify Injector Operation

Using a scan tool or oscilloscope:

Monitor:

Abnormal injector waveforms frequently identify injector failures before complete electrical failure occurs.

Step 13 – Verify Fuel Pressure

Although fuel pressure does not directly cause P0204, verify:

Fuel delivery problems may exist alongside injector circuit faults.

Step 14 – Review Technical Service Bulletins

Before replacing expensive components:

Review manufacturer Technical Service Bulletins (TSBs).

Look for:

Some manufacturers have released revised injector harnesses for known reliability issues.

Step 15 – Verify Charging System Operation

Measure charging voltage.

Normal charging voltage:

13.5–14.8 volts

Charging system problems may interfere with injector driver operation.

Step 16 – Inspect PCM Connectors

Inspect PCM electrical connectors for:

Poor PCM connections may interrupt communication with the Cylinder 4 injector.

Step 17 – Perform a Wiggle Test

While monitoring live injector data:

Move:

Watch for:

If symptoms change while moving the wiring, carefully inspect that section of the harness.

Step 18 – Perform a Road Test

Drive the vehicle while monitoring:

Attempt to duplicate the customer’s complaint under similar operating conditions.

Step 19 – Perform an Injector Balance Test

If equipment is available:

Perform an injector balance test.

Compare Cylinder 4 fuel delivery with the remaining cylinders.

Large differences may indicate:

Step 20 – Confirm the Diagnosis

Before replacing major components, verify:

Completing these diagnostic procedures prevents unnecessary injector and PCM replacement while accurately identifying the root cause of P0204.

Step 21 – Replace the Cylinder 4 Fuel Injector

If testing confirms the Cylinder 4 fuel injector has failed electrically, replacement is the proper repair.

General replacement procedure:

  1. Relieve fuel system pressure.
  2. Disconnect the negative battery cable.
  3. Remove any intake components necessary to access the fuel rail.
  4. Disconnect the Cylinder 4 injector electrical connector.
  5. Remove the fuel rail if required.
  6. Remove the faulty injector.
  7. Inspect the injector bore and O-rings.
  8. Lubricate new O-rings with clean engine oil.
  9. Install an OEM or high-quality replacement injector.
  10. Reinstall the fuel rail and reconnect all electrical connectors.
  11. Clear diagnostic trouble codes.
  12. Verify proper injector operation using a professional scan tool.

Whenever replacing a single injector on a high-mileage engine, inspect the remaining injectors for similar wear.

Step 22 – Repair Wiring Problems

Electrical wiring failures are among the most common causes of P0204.

Inspect and repair:

For permanent repairs:

Temporary wiring repairs frequently lead to repeat failures.

Step 23 – Repair the Cylinder 4 Injector Connector

Inspect the Cylinder 4 injector connector carefully.

Repair:

Poor terminal contact is one of the leading causes of P0204.

Step 24 – Repair Open or Short Circuits

Since P0204 identifies an electrical fault in the Cylinder 4 injector circuit, inspect the complete circuit for:

Pay special attention to wiring routed near:

Heat and engine vibration frequently damage injector wiring over time.

Step 25 – Replace the Injector Fuse or Relay

If voltage is missing at the Cylinder 4 injector:

Inspect:

Replace:

Always determine why a fuse failed before replacing it.

Step 26 – Repair Ground Circuit Problems

Inspect injector ground circuits for:

Poor ground integrity may prevent the PCM from properly controlling the Cylinder 4 injector.

Step 27 – Verify PCM Injector Driver Operation

If the injector, wiring, power supply, and grounds test correctly:

Inspect:

A failed injector driver can disable the Cylinder 4 injector even though every other component tests normally.

PCM replacement should only be considered after all electrical testing has been completed.

Step 28 – Update PCM Software

Before replacing expensive electronic components:

Review manufacturer Technical Service Bulletins (TSBs).

Manufacturers occasionally release software updates correcting:

Always verify the PCM has the latest available calibration.

Step 29 – Verify Fuel Delivery

After repairs:

Verify:

Cylinder 4 should now receive fuel consistently under all operating conditions.

Step 30 – Verify Proper System Operation

After repairs:

Monitor:

Perform:

Verify Cylinder 4 operates normally without misfires or injector circuit faults.

How to Fix P0204

The proper repair depends entirely on the diagnostic results.

Common repairs include:

Verifying the Repair

After completing repairs:

  1. Clear all diagnostic trouble codes.
  2. Start the engine.
  3. Verify smooth idle quality.
  4. Monitor Cylinder 4 injector pulse using a scan tool.
  5. Confirm normal fuel trim values.
  6. Perform a complete road test.
  7. Complete an OBD-II drive cycle.
  8. Verify no pending or permanent DTCs return.
  9. Confirm Cylinder 4 contributes normally under idle, cruise, and heavy-load conditions.

A successful repair restores proper fuel delivery, engine performance, fuel economy, emissions compliance, and long-term reliability.

Typical Repair Costs

RepairTypical Cost
Professional diagnosis$100–250
Cylinder 4 fuel injector replacement$150–600
Injector wiring repair$100–500
Injector connector replacement$75–250
Injector fuse replacement$10–50
Injector relay replacement$30–150
Fuel rail removal labor$150–600
PCM software update$100–250
PCM replacement$900–2,500+

Repair costs vary depending on engine design, injector accessibility, and regional labor rates.

Common Diagnostic Mistakes

Avoid these common mistakes:

Many P0204 repairs involve correcting wiring or connector problems rather than replacing the injector itself.

Manufacturer-Specific Notes

Ford/Lincoln

Inspect:

EcoBoost and Power Stroke engines commonly experience injector harness failures caused by heat and vibration.

General Motors (Chevrolet, GMC, Cadillac, Buick)

Verify:

GM engines often identify injector circuit faults before severe drivability symptoms develop.

Chrysler, Dodge, Jeep, Ram

Inspect:

Harness damage near the intake manifold is a common failure point.

Toyota/Lexus

Inspect:

Electrical faults occur much more frequently than PCM failures.

Nissan/Infiniti

Verify:

Turbocharged direct-injection engines rely heavily on precise injector control for performance and emissions.

Hyundai/Kia

Inspect:

Loose connector terminals are a common source of intermittent injector faults.

Frequently Asked Questions

What usually fixes P0204?

The most common repairs include replacing the Cylinder 4 fuel injector, repairing damaged wiring, replacing injector connectors, repairing open or short circuits, replacing blown injector fuses or relays, repairing ground circuits, or updating PCM software.

Can I drive with P0204?

Limited driving may be possible if the engine runs relatively smoothly, but repairs should be completed immediately. Driving with a Cylinder 4 injector circuit fault can cause persistent misfires, catalytic converter damage, reduced fuel economy, and poor engine performance.

Does P0204 always mean the injector is bad?

No. Damaged wiring, loose connectors, blown fuses, faulty relays, injector driver failures, poor ground connections, and PCM software issues can all trigger P0204 without a failed injector.

Can bad wiring cause P0204?

Absolutely. Broken wiring, melted insulation, connector corrosion, loose terminals, damaged harnesses, and high-resistance circuits are among the most common causes of P0204.

Is P0204 a serious code?

Yes. P0204 is generally considered a moderate-to-high severity diagnostic trouble code. If left unresolved, it can cause continuous Cylinder 4 misfires, poor fuel economy, catalytic converter damage, increased emissions, hard starting, and reduced engine performance.

Final Thoughts

The P0204 Injector Circuit/Open Cylinder 4 code indicates the PCM has detected an electrical fault affecting the Cylinder 4 fuel injector circuit. In most cases, the root cause is a failed injector, damaged wiring, loose connector, blown fuse, faulty relay, or PCM injector driver problem, not a failed PCM.

A complete diagnosis should always verify:

Following a structured diagnostic process prevents unnecessary parts replacement while restoring proper fuel delivery, smooth engine performance, improved fuel economy, emissions compliance, and long-term reliability.

Continue Your Pro Street Fuel Injector Series

Related guides include:

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