Cylinder Deactivation (Active Fuel Management) System Diagnosis

Cylinder Deactivation (Active Fuel Management) System Diagnosis

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview

Circuit/System 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, 3, and 5. The VLOM consists of 3 electrically operated normally closed solenoids, which directs pressurized engine oil to 6 deactivating valve lifters. All 3 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 V3 mode are met, the ECM will command the low side driver to turn ON, in engine firing order sequence

Diagnostic Aids

The valve lifter oil manifold (VLOM) solenoids are assigned to the following engine cylinders:

* Solenoid #1 = Cylinder #1
* Solenoid #2 = Cylinder #3
* Solenoid #3 = Cylinder #5

Important: This test procedure requires that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test. Battery Inspection/Test

1. Ignition ON, engine OFF, measure and record the ignition voltage at the fuse for the VLOM assembly.
2. Remove the fuse for the VLOM assembly from the underhood fuse block.
3. Connect a DMM in series with a 15A fused jumper wire and a non-fused jumper wire across the exposed fuse terminals in the underhood fuse block.
4. Select the 10 A range and zero out the DMM display.
5. Command each VLOM solenoid ON, with a scan tool.
6. Record the amperage reading display on the DMM for each solenoid.
7. Calculate the resistance for each solenoid circuit; divide the previously recorded voltage by the amperage for each VLOM solenoid circuit. The total resistance for each solenoid circuit should be within 11-22 ohms.

^ If the total circuit resistance exceeds 22 ohms, then an open/high resistance condition exists in the VLOM solenoid circuit.

Circuit/System Verification

1. If any DTCs are set, then repair those DTCs first. Go to Diagnostic System Check - Vehicle. Initial Inspection and Diagnostic Overview
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. 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 engine control module (ECM) to command V3 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 with V3 mode operation.

^ 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 V3 mode.
^ If the vehicle does not pass the Circuit/System Verification, then review the cylinder deactivation inhibit reasons listed on the scan tool.

Circuit/System Testing

Electrical System Testing

Ignition ON, engine OFF, command each valve lifter oil manifold (VLOM) solenoid ON, and OFF, using the scan tool. Standing next to the engine compartment, you should be able to hear the solenoids energize, and de-energize with each command.

If you cannot here each solenoid energize and de-energize, then refer to DTC P3401, P3417, or P3433. P3401 P3417 P3433

Mechanical System Testing

1. Connect a vacuum gage to the EVAP vacuum tube fitting on the electronic throttle body. Do not use a compound pressure and vacuum gage. The vacuum gage on a hand held vacuum pump will work fine for this test.
2. Start the engine. Allow the engine to reach normal operating temperature.
3. With a scan tool, command each VLOM solenoid ON, one at a time. Each time a solenoid is commanded 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 Compression Test. Component Tests and General Diagnostics

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests