Sierra 2500 Denali 60L Valve Deactivation Solenoid Diagrams
of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when
operating in V4 mode cylinder deactivation mode.
During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. To help prevent spark plug fouling, the
ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met
and maintained for cylinder deactivation operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, then
return to V8 mode for 1 minute.
Switching between V8 and V4 modes is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle
operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the VLOM solenoids to energize, and the
time for the valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.
Valve Lifter Oil Manifold (VLOM) Assembly
The cylinder deactivation system uses an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM is bolted
to the top of the engine valley, below the intake manifold assembly. The VLOM consists of 4 electrically operated normally closed solenoids. Each
solenoid controls the application of engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure
is routed to the VLOM assembly from an internal oil passage on the rear of the cylinder block.
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 a low side driver internal to the engine control module (ECM).
When all enabling conditions are met for cylinder deactivation, the ECM will ground each solenoid control circuit in firing order sequence, allowing
current to flow through the solenoid windings. With the coil windings energized, the solenoid valve opens, redirecting engine oil pressure through the
VLOM into 8 separate vertical passages in the engine lifter valley. The 8 vertical passages, 2 per cylinder, are connected to the valve lifter bores of the
cylinders to be deactivated. When vehicle-operating conditions require a return to V8 mode, the ECM will turn OFF the control circuit for the solenoids,
allowing the solenoid valves to close. With the solenoid valves closed, engine oil pressure in the control ports is exhausted through the body of the
solenoids into the engine block lifter valley. The housing of the VLOM incorporates several bleeds in the oil passages to purge any air trapped in the
VLOM or engine block.
To help control contamination to the hydraulic circuits, a small replaceable oil screen is located in the VLOM oil inlet passage, below the oil pressure
sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.
During service, use extreme care in keeping the VLOM assembly free of any contamination or foreign material.
Cylinder deactivation may be inhibited for many reasons including the following:
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Engine coolant temperature out of range for cylinder activation
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Engine vacuum out of range
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Brake booster vacuum out of range
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Transmission gear incorrect or shift in progress
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Accelerator pedal out of range or rate of pedal application to fast
*
Engine oil pressure and temperature out of range
*
Engine speed of range
*
Vehicle speed out of range
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Minimum time in V8 mode not met
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Maximum V4 mode time exceeded
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Decel fuel cutoff active
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Reduced engine power active
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Torque management active
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Catalytic converter over temperature protection active
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Piston protection active, knock detected
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Cylinder deactivation solenoid driver circuit faults
