🚨 Diagnostic Profile
Vehicle/Equipment Make: BUICK
Technical Description: IC Output High/Pulse Detected When Grounded Cyl.4
This diagnostic trouble code relates to the Ignition Control (IC) circuit monitored by the Powertrain Control Module (PCM). The PCM expects to see a specific voltage transition (pulse) on the IC circuit for Cylinder 4 when the corresponding ignition driver is commanded to ground. If the PCM detects that the signal remains high or fails to pulse correctly when grounded, it indicates a fault in the ignition control circuit, the ignition module, the coil driver, or the wiring harness connecting these components for Cylinder 4.
🚨 Repair Difficulty Tier
Difficulty Rating: Intermediate
This repair requires the use of a digital multimeter and a capable scan tool to monitor live ignition control circuit data. While it does not involve airbags, restraints, or CAN bus module flashing, it does require knowledge of ignition system wiring diagrams and comfort working around high-voltage ignition components. DIY mechanics with intermediate electrical diagnostic experience can often complete this repair, but accurate circuit testing is essential to avoid misdiagnosis.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
Begin with a visual inspection of the ignition system wiring harness, specifically focusing on the connector and wiring for Cylinder 4’s ignition coil or module. Look for signs of corrosion, chafing, melted insulation, or loose connections at the ignition control module and PCM connector. Inspect the ground straps and chassis grounds near the ignition system, as a poor ground connection can mimic this fault. Check for aftermarket modifications or recent repairs that may have disturbed the Cylinder 4 ignition circuit.
Step 2: Diagnostic Verification
Using a scan tool, access live data for the Ignition Control circuits and monitor Cylinder 4 specifically during a crank or running test if safely possible. Compare the voltage pulse pattern against known-good Cylinder 4 waveform specifications (typically a clean 0-5V or 0-12V square wave pulse depending on system design). Next, backprobe the IC circuit wire for Cylinder 4 at the PCM connector using a digital multimeter set to DC voltage, and observe whether the voltage toggles appropriately when the engine is cranked. A multimeter reading that stays pegged high (near system voltage) with no pulsing confirms the fault is either in the ignition module driver, the wiring harness, or a poor PCM ground reference. Also test continuity and resistance across the Cylinder 4 ignition coil primary windings to rule out an open or shorted coil.
Step 3: Resolution & Reset Process
If the ignition module or coil driver for Cylinder 4 is found to be internally faulty (common failure point), replace the ignition control module or individual ignition coil assembly as applicable to this Buick platform. If wiring damage or a poor ground is identified, repair or replace the damaged harness section and ensure a clean, corrosion-free ground connection. After component replacement, clear the diagnostic trouble codes using a scan tool, then perform a drive cycle or cold-start test to confirm the IC circuit now pulses correctly and the code does not reset. Finally, verify no related codes (such as misfire codes for Cylinder 4) remain active.
📦 Parts, Labor, and Budget Estimates
Required Components/Software: Ignition Control Module (ICM) or Coil-on-Plug assembly for Cylinder 4, wiring harness repair kit/connector pigtail, digital multimeter, and OEM-level or aftermarket scan tool capable of reading live ignition control data.
Average Component Price: $45 – $180 for an individual ignition coil or module (depending on Buick model/engine), plus $15 – $40 for wiring harness repair connectors if needed.
Estimated Labor Hours: 0.5 to 1.5 hours for diagnostic testing, plus an additional 0.5 to 1.0 hour for component replacement, totaling approximately 1.0 to 2.5 hours of standard shop labor.