🚨 Diagnostic Profile
Vehicle/Equipment Make: BUICK
Technical Description: IC Cylinder 4 Not Toggling After Enable
This diagnostic trouble code/condition indicates that the Engine Control Module (ECM) has commanded Active Fuel Management (AFM) / Dynamic Fuel Management (DFM) to deactivate Cylinder 4 as part of the cylinder deactivation sequence, but the system has failed to detect the expected valve toggling (lifter collapse/expansion) response. This typically points to a hydraulic, electrical, or mechanical fault within the AFM lifter or solenoid circuit responsible for Cylinder 4.
🚨 Repair Difficulty Tier
Difficulty Rating: Intermediate to Professional Only
This repair requires a bi-directional scan tool capable of commanding individual AFM solenoids, as well as the mechanical knowledge to access and replace lifters or solenoids under the intake manifold/valley cover. In most cases, this job also requires oil pressure testing and possible valve train disassembly, pushing it toward Professional Only if the lifter or oil manifold assembly needs replacement. Basic electrical diagnosis (wiring/connector checks) can be performed by an Intermediate level technician with proper tools.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Visually inspect the wiring harness and connector leading to the Cylinder 4 AFM solenoid for corrosion, chafing, or disconnection.
- Check engine oil level and condition — low oil level or sludge buildup can prevent proper hydraulic lifter collapse.
- Inspect the oil control valve (OCV) manifold/valley cover gasket for signs of oil leakage or pressure loss near Cylinder 4.
- Confirm there are no related stored codes (e.g., P0300s, P0012/P0017 for cam timing, or additional AFM-specific codes) that could indicate a broader oil pressure or timing issue.
Step 2: Diagnostic Verification
- Connect a bi-directional scan tool and command the Cylinder 4 AFM solenoid ON/OFF while monitoring live toggle status data.
- Use a digital multimeter to check resistance across the Cylinder 4 solenoid connector (compare to OEM specification, typically 4-6 ohms) to rule out an open or shorted coil.
- Perform an oil pressure test at the AFM oil manifold while the solenoid is actively commanded to confirm adequate hydraulic pressure (should typically read within 15-30 PSI range during activation, depending on platform).
- If available, use an oscilloscope to verify the solenoid receives a proper PWM signal from the ECM during the toggle command.
Step 3: Resolution & Reset Process
- If the wiring or connector is damaged, repair or replace the harness section and solenoid connector.
- If the solenoid coil resistance is out of spec, replace the Cylinder 4 AFM solenoid assembly.
- If oil pressure is insufficient at the manifold, inspect and clean/replace the oil control valve filter screen, or replace the lifter assembly if mechanically seized or worn.
- After repair, clear all stored DTCs and perform an ECM relearn/reset procedure for the AFM system using the scan tool.
- Conduct a final road test while monitoring live AFM cylinder toggle data to confirm Cylinder 4 is now activating/deactivating correctly under commanded conditions.
📦 Parts, Labor, and Budget Estimates
Required Components/Software: AFM/DFM Lifter Assembly (Cylinder 4), AFM Oil Control Solenoid, Valley Cover Gasket Kit, Bi-Directional Scan Tool (e.g., Tech2/MDI2 or equivalent aftermarket tool), Oil Pressure Test Kit
Average Component Price: $150 – $450 (lifter assembly and solenoid combined); Valley cover gasket kit: $40 – $80; Dealer programming/reset (if required): $100 – $150
Estimated Labor Hours: 3.5 – 6.0 hours (includes diagnostic time, intake/valley cover removal, lifter or solenoid replacement, and system relearn/verification)