Displacement On Demand (DOD) System Diagnosis

DISPLACEMENT ON DEMAND (DOD) SYSTEM DIAGNOSIS

CIRCUIT DESCRIPTION
To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the displacement on demand (DoD) system ON to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The DoD systems use an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM consists of 4 electrically operated normally closed solenoids that directs engine oil pressure to the deactivating DoD valve lifters. All 4 VLOM solenoids are connected in parallel to a fused ignition 1 voltage circuit supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to an individual low side driver internal to the ECM. When all enabling conditions for V4 mode are met, the ECM will command the low side driver to turn ON, grounding each VLOM solenoid control circuit, in engine firing order sequence.

TEST DESCRIPTION

Steps 1 - 5:

The numbers below refer to the step numbers on the diagnostic table.
2. A functional service bay test is performed to determine if the cylinders can deactivate. The vacuum gage will display a steady regular fluctuating drop of engine vacuum on a cylinder that has both valves deactivated. This test must be performed with a vacuum gage only and not a combination pressure and vacuum gage. The gage on a hand held vacuum pump or Mityvac will work fine for this test.
3. Perform a road test while monitoring the cylinder deactivation data parameters with a scan tool. If the engine does not switch to a V4 mode, then review the inhibit reasons listed in the DoD system description.