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:
- Injector voltage
- Injector current
- Injector pulse width
- Circuit continuity
- Injector driver operation
- Engine operating conditions
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:
- Failed Cylinder 4 fuel injector
- Open injector circuit
- Short-to-ground
- Short-to-voltage
- Damaged injector wiring
- Loose injector connector
- Connector corrosion
- Failed PCM injector driver
- High circuit resistance
- Failed PCM (rare)
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:
- Battery voltage
- PCM-controlled ground pulse
- Current monitoring
- Electrical feedback
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:
- Electromagnetic coil
- Injector pintle
- Nozzle
- Internal spring
- Electrical connector
- Fuel inlet
When energized by the PCM:
- The injector opens.
- Fuel enters the engine.
- The injector closes once the pulse ends.
This process occurs thousands of times per minute.
Why Proper Injector Operation Matters
Accurate injector control is critical for:
- Air/fuel ratio
- Engine performance
- Fuel economy
- Emissions control
- Smooth idle
- Cold starting
- Turbocharger protection
- Catalytic converter protection
A malfunctioning Cylinder 4 injector circuit may cause:
- Cylinder misfires
- Rough idle
- Hesitation
- Poor acceleration
- Increased fuel consumption
- Elevated emissions
Ignoring the problem may eventually damage the catalytic converter.
How the PCM Detects P0204
The PCM continuously monitors:
- Injector voltage
- Injector current
- Injector pulse
- Circuit continuity
- Engine RPM
- Oxygen sensor feedback
- Crankshaft speed
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:
- Failed injector coil
- Open circuit
- Broken wiring
- Loose connector
- Connector corrosion
- High electrical resistance
- Failed PCM injector driver
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:
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Loose terminals
- Connector corrosion
- Oil contamination
- Rodent damage
Heat and engine vibration often damage injector wiring over time.
Can the Fuel Injector Fail?
Yes.
Fuel injectors commonly fail due to:
- Open internal coil
- Internal short circuit
- High coil resistance
- Heat damage
- Fuel contamination
- Internal corrosion
- Age-related wear
- Manufacturing defects
Electrical injector failures commonly trigger P0204.
Mechanical injector failures may also generate:
- Misfire codes
- Lean condition codes
- Rich condition codes
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:
- Lean fuel mixture
- Poor acceleration
- Hard starting
- Misfires
Fuel pressure should still be verified because multiple faults can occur simultaneously.
P0204 Quick Facts
| Item | Information |
|---|---|
| DTC | P0204 |
| Generic Definition | Injector Circuit/Open Cylinder 4 |
| System | Fuel Injection / Powertrain |
| Severity | Moderate to High |
| Safe to Drive? | Limited driving only |
| Common Symptoms | Check Engine Light, Cylinder 4 misfire, rough idle, poor acceleration |
| Common Causes | Failed injector, damaged wiring, loose connector, PCM injector driver |
| Typical Repair Cost | $150–1,500+ |
| Related Codes | P0200, P0201, P0202, P0203, P0205–P0212, P0304, P0171, P0172 |
Common Vehicles That Experience P0204
P0204 commonly appears on:
- Ford
- Lincoln
- Chevrolet
- GMC
- Cadillac
- Dodge
- Ram
- Jeep
- Chrysler
- Toyota
- Lexus
- Nissan
- Infiniti
- Honda
- Acura
- Hyundai
- Kia
- Volkswagen
- Audi
- BMW
- Mercedes-Benz
The code is especially common on:
- High-mileage vehicles
- Turbocharged engines
- Gasoline direct injection (GDI) engines
- Diesel engines
- Fleet vehicles
- Engines exposed to excessive heat and vibration
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:
- The injector must be replaced.
- Fuel pressure is low.
- The fuel pump has failed.
- Cylinder 4 has internal engine damage.
- The PCM has failed.
Instead, it means the PCM has detected an electrical malfunction affecting the Cylinder 4 injector circuit.
The underlying problem may involve:
- Cylinder 4 fuel injector
- Injector wiring harness
- Electrical connector
- Power supply
- Ground circuit
- PCM injector driver
- PCM (rare)
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:
- Failed Cylinder 4 fuel injector
- Open injector circuit
- Short-to-ground
- Short-to-voltage
- Damaged injector wiring
- Loose electrical connector
- Connector corrosion
- Blown injector fuse
- Failed injector relay
- PCM injector driver
- Failed PCM (rare)
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:
- Park on level ground.
- Apply the parking brake.
- Allow the engine to cool.
- Wear safety glasses.
- Wear protective gloves.
- Disconnect the battery before repairing wiring.
- Keep sparks and open flames away from the fuel system.
Fuel injectors operate under high fuel pressure, making proper safety procedures essential.
Tools Required
Professional diagnosis may require:
- Professional scan tool
- Digital multimeter
- Noid light kit
- Automotive oscilloscope (recommended)
- Fuel pressure gauge
- Manufacturer wiring diagrams
- Test light
- Back-probe pins
- Basic hand tools
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:
- Stored DTCs
- Pending DTCs
- Permanent DTCs
- Freeze-frame data
Monitor:
- Cylinder 4 injector pulse width
- Short-Term Fuel Trim (STFT)
- Long-Term Fuel Trim (LTFT)
- Engine RPM
- Battery voltage
Never erase codes before recording freeze-frame information.
Step 2 – Check for Related Trouble Codes
P0204 commonly appears with:
- P0200
- P0201
- P0202
- P0203
- P0205–P0212
- P0304
- P0171
- P0172
- Fuel pressure codes
Related injector and fuel system codes often simplify diagnosis.
| Code Combination | Likely Diagnosis |
|---|---|
| P0204 only | Cylinder 4 injector circuit fault |
| P0204 + P0304 | Injector causing Cylinder 4 misfire |
| P0204 + P0171 | Lean condition caused by poor fuel delivery |
| P0204 + P0172 | Injector leaking or driver fault |
| P0204 + P0200 | General injector circuit problem |
Repair obvious electrical faults before replacing the injector.
Step 3 – Review Freeze-Frame Data
Review:
- Engine RPM
- Vehicle speed
- Engine load
- Fuel trims
- Injector pulse width
- Battery voltage
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:
- Engine off: 12.4–12.8 volts
- Engine running: 13.5–14.8 volts
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:
- Physical damage
- Fuel leaks
- Cracked injector body
- Loose connector
- Burned terminals
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:
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Heat damage
- Oil contamination
- Rodent damage
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:
- Corrosion
- Bent terminals
- Loose connector pins
- Broken locking tab
- Moisture intrusion
- Oil contamination
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:
- Injector fuse
- Injector relay
- Wiring harness
- Power distribution circuit
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:
- Open circuit
- Internal short
- Excessive resistance
- Resistance outside specification
Step 10 – Verify Injector Pulse
Install a noid light or connect an oscilloscope.
Crank or start the engine.
Verify:
- Injector pulse
- Pulse consistency
- PCM control
If no injector pulse exists:
Inspect:
- PCM injector driver
- Crankshaft Position Sensor
- Camshaft Position Sensor
- Injector power supply
Step 11 – Perform Voltage Drop Testing
Measure voltage drop across:
- Injector power circuit
- Injector ground circuit
Inspect for:
- High resistance
- Loose terminals
- Poor grounds
- Damaged wiring
Even minor resistance can reduce injector performance.
Step 12 – Verify Injector Operation
Using a scan tool or oscilloscope:
Monitor:
- Injector pulse width
- Current ramp
- Injector response
- Misfire counters
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 pressure
- Fuel pressure regulator operation
- Fuel pump output
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:
- Injector harness revisions
- PCM software updates
- Injector connector updates
- Injector driver improvements
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:
- Corrosion
- Bent terminals
- Loose locking tabs
- Moisture intrusion
Poor PCM connections may interrupt communication with the Cylinder 4 injector.
Step 17 – Perform a Wiggle Test
While monitoring live injector data:
Move:
- Cylinder 4 injector connector
- Injector wiring harness
- PCM connector
Watch for:
- Injector pulse loss
- Misfire counts
- Engine stumble
- Fuel trim changes
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:
- Cylinder 4 injector pulse width
- Fuel trims
- Misfire counters
- Engine RPM
- Engine load
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:
- Failing injector
- Electrical injector fault
- Restricted injector
- Wiring problem
Step 20 – Confirm the Diagnosis
Before replacing major components, verify:
- Cylinder 4 injector resistance
- Injector pulse
- Wiring continuity
- Injector voltage supply
- Ground integrity
- Fuse condition
- Relay operation
- Fuel pressure
- PCM connector condition
- PCM software
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:
- Relieve fuel system pressure.
- Disconnect the negative battery cable.
- Remove any intake components necessary to access the fuel rail.
- Disconnect the Cylinder 4 injector electrical connector.
- Remove the fuel rail if required.
- Remove the faulty injector.
- Inspect the injector bore and O-rings.
- Lubricate new O-rings with clean engine oil.
- Install an OEM or high-quality replacement injector.
- Reinstall the fuel rail and reconnect all electrical connectors.
- Clear diagnostic trouble codes.
- 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:
- Broken wiring
- Chafed insulation
- Melted wiring
- Pinched harnesses
- Heat-damaged wiring
- Rodent damage
- High-resistance circuits
For permanent repairs:
- Replace damaged wire sections
- Solder all splices
- Protect repairs with adhesive-lined heat-shrink tubing
- Secure the harness away from exhaust components and moving engine parts
Temporary wiring repairs frequently lead to repeat failures.
Step 23 – Repair the Cylinder 4 Injector Connector
Inspect the Cylinder 4 injector connector carefully.
Repair:
- Corroded terminals
- Bent connector pins
- Loose terminal tension
- Oil contamination
- Moisture intrusion
- Broken locking tabs
- Damaged connector housing
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:
- Open circuits
- Short-to-ground
- Short-to-voltage
- Broken conductors
- Damaged insulation
- Loose splice repairs
- Harness damage
Pay special attention to wiring routed near:
- Exhaust manifolds
- Turbochargers
- Valve covers
- Engine mounts
- Previous repair locations
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:
- Injector fuse
- Injector relay
- Fuse box terminals
- Power distribution module
Replace:
- Blown fuses
- Faulty relays
- Burned fuse holders
Always determine why a fuse failed before replacing it.
Step 26 – Repair Ground Circuit Problems
Inspect injector ground circuits for:
- Loose ground connections
- Corroded terminals
- High resistance
- Broken ground wires
- Damaged engine grounds
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:
- PCM injector driver output
- Driver voltage
- Driver current
- PCM connector terminals
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:
- False injector circuit detection
- Injector driver calibration
- Fuel injection strategy
- Misfire detection logic
Always verify the PCM has the latest available calibration.
Step 29 – Verify Fuel Delivery
After repairs:
Verify:
- Fuel pressure
- Injector pulse width
- Fuel trims
- Cylinder contribution
- Engine idle quality
Cylinder 4 should now receive fuel consistently under all operating conditions.
Step 30 – Verify Proper System Operation
After repairs:
Monitor:
- Cylinder 4 injector pulse width
- Short-Term Fuel Trim
- Long-Term Fuel Trim
- Misfire counters
- Engine RPM
- Pending DTCs
Perform:
- Cold start
- Idle test
- Highway driving
- Heavy acceleration
- Complete OBD-II drive cycle
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:
- Replacing the Cylinder 4 fuel injector
- Repairing damaged wiring
- Repairing open circuits
- Repairing short circuits
- Cleaning or replacing the injector connector
- Replacing the injector fuse
- Replacing the injector relay
- Repairing ground circuits
- Updating PCM software
- Replacing the PCM injector driver or PCM (rare)
Verifying the Repair
After completing repairs:
- Clear all diagnostic trouble codes.
- Start the engine.
- Verify smooth idle quality.
- Monitor Cylinder 4 injector pulse using a scan tool.
- Confirm normal fuel trim values.
- Perform a complete road test.
- Complete an OBD-II drive cycle.
- Verify no pending or permanent DTCs return.
- 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
| Repair | Typical 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:
- Replacing the injector before checking wiring integrity
- Ignoring damaged injector connectors
- Failing to test injector resistance
- Overlooking blown injector fuses
- Ignoring voltage drop in power or ground circuits
- Clearing codes before recording freeze-frame data
- Skipping Technical Service Bulletins
- Replacing the PCM before verifying injector driver output
Many P0204 repairs involve correcting wiring or connector problems rather than replacing the injector itself.
Manufacturer-Specific Notes
Ford/Lincoln
Inspect:
- Cylinder 4 injector harness
- PCM injector driver
- Injector connector
- Fuse box terminals
EcoBoost and Power Stroke engines commonly experience injector harness failures caused by heat and vibration.
General Motors (Chevrolet, GMC, Cadillac, Buick)
Verify:
- Injector pulse width
- Injector resistance
- Wiring continuity
- Cylinder contribution
GM engines often identify injector circuit faults before severe drivability symptoms develop.
Chrysler, Dodge, Jeep, Ram
Inspect:
- Injector harness routing
- ASD (Automatic Shutdown) relay
- Injector connectors
- PCM driver circuits
Harness damage near the intake manifold is a common failure point.
Toyota/Lexus
Inspect:
- Injector resistance
- Connector terminals
- Wiring continuity
- PCM connector condition
Electrical faults occur much more frequently than PCM failures.
Nissan/Infiniti
Verify:
- Injector pulse
- Harness condition
- Injector resistance
- ECM software
Turbocharged direct-injection engines rely heavily on precise injector control for performance and emissions.
Hyundai/Kia
Inspect:
- Injector wiring
- Connector terminals
- Ground circuits
- Injector driver operation
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:
- Cylinder 4 injector resistance
- Injector pulse
- Wiring continuity
- Power supply voltage
- Ground integrity
- Injector fuse and relay operation
- Fuel pressure
- PCM connector condition
- PCM software version
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
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