Fuel Delivery

Gold ChapterATLAS-FUEL-0007Template 2.2

P0204

Injector Circuit/Open - Cylinder 4

P0204 indicates the PCM detected an electrical fault in the cylinder 4 injector circuit.

SeverityMedium-high
DriveabilityA dead or uncontrolled injector circuit can cause a hard misfire and catalyst-damaging unburned fuel. Avoid extended driving with an active cylinder misfire or flashing MIL.
Diagnostic Time30-90 minutes
Typical Cost$50-$900+
Atlas StatusGold Chapter
Reviewed2026-08

Diagnostic Snapshot

Most Common Cause: Open injector circuit or failed injector coil on cylinder 4Engine Damage Risk: Low to ModerateSafe to Drive: A dead or uncontrolled injector circuit can cause a hard misfire and catalyst-damaging unburned fuel. Avoid extended driving with an active cylinder misfire or flashing MIL.Professional Scan Tool: Strongly recommended; graphing, enhanced data, and bidirectional controls materially improve diagnostic confidenceMechanical Test Recommended: Yes — independently verify the physical system condition indicated by scan/electrical evidenceDIY Difficulty: Moderate

Atlas Academy

Learn the System

Before diagnosing this code, it helps to understand the system behind it.

Read Understanding Fuel Delivery Systems

Technical Summary

P0204 indicates the PCM detected an electrical fault in the cylinder 4 injector circuit.

Final QA emphasis: P0204 requires correlation of cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution. The code should be diagnosed by reproducing the enable condition, proving loaded electrical integrity, and independently confirming the physical system. OEM thresholds and system design take priority over universal values.

What You'll Learn

  • Understand what an injector circuit fault on cylinder 4 means
  • Separate injector, connector, harness, power-supply, and PCM-driver faults
  • Use resistance, noid-light, voltage, and waveform testing correctly
  • Inspect terminal tension and intermittent wiring problems
  • Avoid replacing the injector before proving the electrical fault

Think Like a Technician

Do not replace the injector because the code names it. Determine whether the injector, connector, harness, power supply, or PCM driver has failed.

For P0204, ask three questions in order: what did the controller command or observe, can the circuit carry and report that condition correctly, and did the physical system actually respond? Use cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution to identify which layer fails first.

What This Code Means

The PCM cannot properly monitor or control injector 4.

System Overview

Learn injector circuit operation before diagnosing P0204.

Why This Code Sets

Injector 4 circuit is open, shorted, or has excessive resistance.

Common Symptoms

  • Check Engine Light
  • Rough idle
  • Misfire on cylinder 4
  • Reduced power
  • Hard starting
  • Poor fuel economy

Most Likely Causes

  • 1. open/high-resistance injector control circuit or poor connector terminal
  • 2. injector coil/internal electrical fault
  • 3. shared injector power-feed fuse/relay/splice fault
  • 4. control wire short to power/ground or another circuit
  • 5. PCM injector-driver fault after load/circuit proof
  • 6. mechanical injector or cylinder fault accompanying but not causing the circuit code

Common Vehicles

  • Ford
  • GM
  • Ram
  • Toyota
  • Honda

Freeze Frame Clues

Idle

Circuit faults are often present immediately.

Under Load

Harness movement may expose intermittent faults.

Live Data Expectations

Injector pulse width and cylinder contribution should normalize after repair.

Typical Verification Tests

  • Injector resistance
  • Noid light test
  • Injector power verification
  • PCM driver verification
  • Wiggle test
  • Oscilloscope waveform

Before You Condemn

  • Verify:
  • Injector resistance
  • Injector power
  • PCM driver
  • Connector condition
  • Harness integrity

Before Replacing Parts

Confirm electrical testing before replacing the injector.

Diagnostic Workflow

  1. Confirm P0204; save current, pending, history, freeze-frame, readiness, misfire/fuel-trim data where applicable, and the complete powertrain scan before clearing codes.
  2. Verify the exact definition — Injector Circuit/Open - Cylinder 4 — and review VIN-specific system design, enabling criteria, fail-safe strategy, wiring, component locations, bulletins, and test procedures.
  3. Prioritize companion DTCs and basic prerequisites: battery/charging voltage, module powers/grounds, engine mechanical condition, coolant temperature plausibility, and any shared reference or network faults.
  4. Recreate the freeze-frame condition safely and graph cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with RPM, load, temperature, vehicle speed, and system voltage.
  5. Inspect the relevant harnesses, connectors, hoses, pipes, grounds, vacuum lines, fuel/exhaust components, and recent repair areas before disconnecting or replacing anything.
  6. Compare commanded and actual data. Decide whether the failure is electrical, hydraulic/pneumatic, mechanical, combustion-related, or a sensor-plausibility problem before choosing the next test.
  7. Perform loaded electrical tests on affected powers, grounds, reference, signal, solenoid, injector, relay, or actuator circuits; static continuity alone is not sufficient for current-carrying circuits.
  8. Use bidirectional controls where supported to command the affected actuator or system and compare command with current/voltage feedback, sensor response, and actual physical operation.
  9. Independently verify the physical condition with the appropriate test: calibrated fuel-pressure equipment, smoke/EVAP test, compression/leak-down, ignition waveform, injector balance, airflow/pressure response, or another OEM-approved method.
  10. Separate bank-specific or cylinder-specific faults from shared-system faults by comparing the opposite bank, neighboring cylinders, redundant sensors, or common feeds under the same operating condition.
  11. Check for heat-, vibration-, and load-dependent failures by repeating the test as the system warms and by carefully manipulating suspect harness sections while monitoring data.
  12. Do not condemn a sensor because its reading is abnormal until an independent measurement establishes whether the sensor is wrong or accurately reporting a real physical fault.
  13. Do not condemn an actuator because it fails to respond until power, ground, control authority, mechanical freedom, and the load side of the circuit are proven.
  14. Before condemning the PCM, prove stable module powers/grounds, terminal tension, external loads, circuit capability, prerequisite inputs, network integrity, and current calibration/software.
  15. Repair only the fault supported by test evidence, then perform any required relearn, adaptation, fuel-trim reset, or monitor-specific service procedure.
  16. Repeat the original enable condition and verify P0204 remains absent current and pending, the monitored data is plausible, driveability is normal, and readiness progresses.

Labor & Inspection Checklist

  • Connector
  • Harness
  • Injector resistance
  • Voltage
  • Driver signal
  • Road test

Shop Notes

  • Connector damage is common.
  • Check terminal tension.
  • Verify injector command before replacement.

Final QA diagnostic boundary for P0204: Injector Circuit/Open - Cylinder 4. The technician should center the diagnosis on cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution rather than treating the DTC as a replacement instruction.

Evidence hierarchy: preserve freeze-frame first; confirm prerequisites second; compare command/input with loaded circuit behavior third; verify the physical system independently fourth. This order prevents a biased PID or unloaded continuity test from driving the repair.

Failure-pattern note: separate faults that follow engine load, heat, vibration, bank, cylinder, key cycle, purge/EGR command, or pressure demand. A repeatable pattern is often more diagnostic than a single static reading.

Before-parts rule: sensors require plausibility proof, actuators require power/ground/control plus mechanical-response proof, and modules require external circuit/load proof. Do not use a code description as proof of component failure.

Safety/driveability note: A dead or uncontrolled injector circuit can cause a hard misfire and catalyst-damaging unburned fuel. Avoid extended driving with an active cylinder misfire or flashing MIL.

Verification standard: reproduce the original enable condition after repair, not merely a warm idle in the bay. Confirm the monitor's related PIDs remain plausible and that no pending code returns.

P0204 QA case-pattern 1: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 2: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 3: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 4: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 5: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 6: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 7: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 8: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 9: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 10: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 11: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 12: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 13: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 14: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

P0204 QA case-pattern 15: Reproduce the original operating condition and compare cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution with an independent physical or electrical measurement. If the scan value changes but the physical system does not, investigate sensor interpretation, control authority, or a mechanical restriction. If the physical system changes but scan feedback does not, investigate the sensing/reference path. If neither changes, prove power, ground, command, and prerequisite conditions before escalating to the controller. Document the before-and-after data so the repair is verified by evidence rather than by the temporary absence of a code.

Mechanic's Tip

Use a noid light and resistance test before replacing any injector.

Common Mistakes

  • Replacing injector first
  • Ignoring wiring
  • Skipping noid light testing

Tools Used During Diagnosis

  • Scan tool
  • Multimeter
  • Noid light
  • Oscilloscope

Customer Explanation

The computer detected an electrical problem affecting the injector circuit for cylinder 4. Testing identifies whether the injector or the circuit is at fault.

Frequently Asked Questions

What does P0204 mean? P0204 is Injector Circuit/Open - Cylinder 4. The monitor is focused on cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution.

Does the code prove a part has failed? No. It identifies a failed monitored relationship. Electrical integrity, physical system behavior, and sensor plausibility must be separated before parts are replaced.

Is it safe to drive with P0204? A dead or uncontrolled injector circuit can cause a hard misfire and catalyst-damaging unburned fuel. Avoid extended driving with an active cylinder misfire or flashing MIL.

What should be checked first? Save freeze-frame and the complete scan, verify the exact system design by VIN, then reproduce the failure while comparing commanded data with actual electrical and physical response.

What freeze-frame clues matter most? RPM, load, vehicle speed, coolant temperature, system voltage, fuel trims, pressure/airflow data, command state, and companion DTCs show whether the failure occurs at idle, startup, cruise, acceleration, deceleration, or high load.

What live data is most useful? Graph cylinder 4 injector driver command, injector power feed, control-circuit voltage/current waveform, connector integrity, coil/load behavior, and cylinder contribution plus system voltage, RPM/load, temperature, and relevant redundant or opposite-bank/cylinder data. Look for the first relationship that breaks.

Can another system create this code? Yes. Shared voltage, airflow, fuel delivery, exhaust, vacuum, mechanical, or combustion faults can make the named monitor fail even when the named component is functional.

Should I replace the most common part first? No. Common-failure statistics are useful for prioritizing inspection, not for skipping tests. Expensive or invasive parts should have at least two consistent forms of evidence.

When is professional equipment justified? Enhanced graphing data and bidirectional controls are strongly recommended. Depending on the code, a pressure transducer/gauge, scope, current clamp, smoke machine, injector balance equipment, or compression/leak-down tools may be justified.

How do I verify the repair? Repeat the original operating condition, confirm electrical and physical results agree, check current and pending codes, and complete enough of the drive cycle to show stable data and readiness progress.

Related Atlas Resources

Atlas Academy

Understanding Fuel Delivery Systems

Related Reference Chapters

Diagnostic Confidence

High

Related Codes

P0201 P0202 P0203 P0304 P0087 P0088 P0191

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Chapter Status

Editorial StatusAtlas Certified
Last Reviewed2026-08
Template Version2.2
Related Academy GuideUnderstanding Fuel Delivery Systems

Why Trust This Guide?

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This guide is maintained for working mechanics, mobile technicians, fleet maintenance professionals, and independent repair shops.