Cylinder Deactivation (Active Fuel Management) System Diagnosis
Cylinder Deactivation (Active Fuel Management) System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit Description
To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the valve lifter oil manifold (VLOM) solenoids ON, to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank. The VLOM consists of 4 electrically operated normally closed solenoids, which directs pressurized engine oil to 8 deactivating valve lifters. All 4 VLOM solenoids are connected in parallel to a fused ignition circuit supplied by the powertrain relay. The control circuit for each solenoid is connected to an individual low side driver internal to the ECM. When enabling conditions for V4 mode are met, the ECM will command each low side driver to turn ON, in engine firing order sequence.
Diagnostic Aids
The VLOM solenoids are assigned to the following engine cylinders:
* Solenoid #1-Cylinder #1
* Solenoid #2-Cylinder #4
* Solenoid #3-Cylinder #6
* Solenoid #4-Cylinder #7
Reference Information
Schematic Reference
Engine Controls Schematics (LZ1) [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
Cylinder Deactivation (Active Fuel Management) System Description Cylinder Deactivation (Active Fuel Management) System Description
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Engine Control Module Scan Tool Information (LZ1 w/Tech 2) Engine Control Module Scan Tool Information (w/Tech 2)Engine Control Module Scan Tool Information (V8 Gasoline) Engine Control Module Scan Tool Information for scan tool information
Circuit/System Verification
1. If any DTCs are set, then repair those DTC first. Refer to Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle.
2. Start and idle the engine.
3. Allow the engine to reach normal engine operating temperature. The engine should idle smoothly without any misfires. If the engine misfires, refer to DTC P0300-P0308 P0300.
4. Monitor the cylinder deactivation system data parameters with a scan tool.
5. Road test the vehicle under light throttle and load conditions that will allow the ECM to command V4 mode. If all enabling conditions are met for cylinder deactivation, and if no internal engine hydraulic/mechanical fault conditions are present, the ECM will continue operation in V4 mode.
• If the vehicle passes the Circuit/System Verification test, then review the active fuel management driving information in the Features and Controls section of the owners manual with the vehicle operator, or instruct the vehicle operator in the proper driving techniques to obtain V4 mode.
• If the vehicle does not pass the Circuit/System Verification test, then review the cylinder deactivation inhibit reasons listed on the scan tool.
Circuit/System Testing
Electrical System Testing
1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description Hybrid Modes of Operation Description.
2. Ignition ON, verify the scan tool hood position parameter displays Open.
• If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
3. Ignition ON and the engine OFF, command each VLOM solenoid ON and OFF using the scan tool. Standing next to the engine compartment, you should be able to hear the solenoid energize and de-energize with each command.
If you cannot hear each solenoid energize and de-energize, then refer to DTC P3401, P3425, P3441, or P3449 P3401.
Mechanical System Testing
1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description Hybrid Modes of Operation Description.
2. Ignition ON, verify the scan tool hood position parameter displays Open.
• If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
3. Connect a vacuum gauge to the EVAP vacuum tube fitting on the electronic throttle body. DO NOT use a compound pressure and vacuum gauge. The vacuum gauge on a hand held vacuum pump will work fine for this test.
4. Start the engine. Allow the engine to reach normal operation temperature.
5. With a scan tool, command each VLOM solenoid ON, one at a time. Each time a solenoid is command ON, you should observe a fluctuating drop of intake manifold vacuum, and a misfire on the cylinder that was deactivated.
• If there is no fluctuating drop in engine vacuum, or the engine does not misfire, then refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
Cylinder Deactivation (Active Fuel Management) System Diagnosis
1. Review the system operation in order to familiarize yourself with the system functions. As required, disable the auto-stop function prior to repair. Refer to Hybrid Modes of Operation Description Hybrid Modes of Operation Description.
2. Measure the engine oil level. Fill, as required.
3. Using the scan tool, inspect for diagnostic codes within the engine control module (ECM). Refer to Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle. Repair, as required.
4. Verify proper engine oil pressure and operation of the active fuel management oil pressure relief valve. Refer to Oil Pressure Diagnosis and Testing Oil Pressure Diagnosis and Testing.
5. Verify proper operation of the active fuel management system components. Refer to Cylinder Deactivation (Active Fuel Management) System Compression Test Cylinder Deactivation (Active Fuel Management) System Compression Test.
6. Remove the valve lifter oil manifold. Refer to Valve Lifter Oil Manifold Replacement Valve Lifter Oil Manifold Replacement.
7. Verify proper operation of the valve lifter oil manifold. Refer to Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing Cylinder Deactivation (Active Fuel Management) Valve Lifter Oil Manifold Diagnosis and Testing.
8. Replace the active fuel management valve lifters, as required. Both intake and exhaust lifters should be replaced in pairs. Refer to Valve Lifter Replacement Valve Lifter Replacement.