🚨 Diagnostic Profile
Vehicle Make: BUICK
Technical Description: Injector Circuit Cylinder 4 Intermittent
This diagnostic code indicates an intermittent electrical fault within the fuel injector circuit specifically tied to Cylinder 4. The Engine Control Module (ECM) is detecting irregular voltage or resistance signals being sent to or from the injector driver circuit, which may cause misfires, rough idle, or reduced fuel efficiency. Because the fault is intermittent rather than constant, it often points to a wiring harness issue, a corroded connector, or a failing injector solenoid rather than a fully dead component.
🚨 Repair Difficulty Tier
Difficulty Level: Intermediate
This repair requires the use of a diagnostic scan tool capable of reading live ECM data streams, along with a digital multimeter to test circuit continuity, resistance, and voltage drop across the injector harness. While it does not involve airbag systems or module flashing in most cases, it does require a working understanding of automotive wiring diagrams and injector pulse-width signals. DIY mechanics with intermediate experience can attempt this repair, but those unfamiliar with electrical diagnostics should consult a professional to avoid misdiagnosis.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
Begin by visually inspecting the engine bay for any obvious signs of damage. Check the wiring harness leading to the Cylinder 4 injector for cracked insulation, chafing, or heat damage near the exhaust manifold. Inspect the injector electrical connector for corrosion, bent pins, or a loose locking tab. Wiggle the harness gently while the engine is idling (if safe to do so) to see if the issue reproduces, which would confirm an intermittent wiring fault rather than a sensor failure.
Step 2: Diagnostic Verification
Connect an OBD-II scan tool and pull live data from the ECM, paying close attention to injector pulse width and fuel trim values for Cylinder 4 compared to the other cylinders. Disconnect the injector connector and use a multimeter to test resistance across the injector terminals; a healthy injector typically reads between 12-16 ohms depending on the vehicle’s fuel system type. Additionally, perform a voltage drop test on the circuit while wiggling the harness to catch any intermittent opens or shorts that may not appear during a static test.
Step 3: Resolution & Reset Process
If the injector itself tests faulty (open or shorted winding), replace the injector with an OEM or OEM-equivalent part and reseat all connectors with dielectric grease to prevent future corrosion. If the wiring harness is damaged, repair or replace the affected harness section, ensuring proper connector locking and strain relief. Once repairs are complete, clear the diagnostic trouble codes using the scan tool and perform a test drive under varied load and RPM conditions to confirm the intermittent fault does not return. Recheck live data to confirm Cylinder 4 injector pulse width and trims are now consistent with the other cylinders.
📦 Parts, Labor, and Budget Estimates
Required Components/Software: OBD-II diagnostic scan tool, digital multimeter, replacement fuel injector (if faulty), wiring harness repair kit or connector pigtail (if damaged), dielectric grease.
Average Component Price: $45 – $150 for a replacement injector (depending on engine type); $20 – $60 for a wiring harness repair kit or connector pigtail.
Estimated Labor Hours: 1.0 – 2.5 hours for diagnosis and circuit testing; an additional 0.5 – 1.5 hours if injector replacement or harness repair is required, depending on engine accessibility.