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gmtech4
gmtech4, Chevy Mechanic
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Experience:  14 yrs GM experience ,
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How can I disable the active fuel management system

Customer Question

No Comment Added
Submitted: 6 years ago.
Category: Chevy
Expert:  gmtech4 replied 6 years ago.
what vehicle do you have and why do you want to disable it?
Expert:  gmtech4 replied 6 years ago.

sorry for this long article it is description and operation and ways that the system will disable itself,

Cylinder Deactivation (Active Fuel Management) System Description

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation 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 engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

When commanded ON, the ECM will determine what cylinder is firing, and begin deactivation on the next closest deactivated cylinder in firing order sequence. The Gen IV engine has a firing order of 1-8-7-2-6-5-4-3. If cylinder number 1 is on its combustion event when cylinder deactivation is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when cylinder deactivation is commanded ON, then the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing. The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When V4 mode is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the internal pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each cylinder deactivation lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the VLOM, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event. During an intake event, the intake cam lobe is pushing the valve lifter upwards to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve. However, when cylinder deactivation is commanded ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately, and deactivate the exhaust valve.

By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge or exhaust gas charge in the combustion chamber. The capture 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. During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. 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, and then return to V8 mode for 1 minute.

Switching between V8 and V4 mode 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.

The cylinder deactivation system consists of the following components:

The VLOM assembly
Eight special valve lifters, 2 per deactivating cylinder
The engine oil pressure regulator valve for cylinder deactivation operation
Gen IV cylinder deactivation engine block
The ECM

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 a 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 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 control any 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.

Engine Control Module (ECM)

The engine control module (ECM) is responsible for the management and control of all engine functions. Each ECM comes equipped with a specific set of software/calibrations designed for that engine and vehicle application. The ECM will determine engine operating parameters, based upon information from a network of switches, sensors, modules and communication with other controllers located throughout vehicle. Internal to the ECM is an integrated circuit device called a low-side driver. The low-side driver is designed to operate internally, like an electronic switch. An individual low-side driver controls each valve lifter oil manifold (VLOM) solenoid. When enabling conditions for V4 mode are met, the ECM will command the low-side driver to ground each VLOM solenoid control circuit, in firing order sequence. Internal to the low-side driver is a fault detection circuit, which monitors the solenoid control circuit for an incorrect voltage level. If an incorrect voltage level, such as an open, high resistance, or short to ground, is detected, the low-side driver, along with the fault detection circuit, will communicate the condition to the central processor in the ECM. The ECM will then command a return to V8 mode, set a corresponding DTC, and illuminate the malfunction indicator lamp (MIL) on the instrument panel.

Cylinder Deactivation Inhibit Reasons

Listed below are the powertrain conditions that will inhibit V4 mode, while operating under light load driving conditions:

Engine manifold vacuum low
Brake booster vacuum pressure low
Accelerator pedal position rate of increase too high, electronic throttle control
Accelerator pedal position too high, electronic throttle control
Ignition voltage out of range
Engine oil pressure out of range
Engine oil temperature out of range
Engine RPM out of range
Transmission gear incorrect
Transmission range incorrect
Transmission gear shift in progress
All cylinders activated via scan tool output control
Minimum time in V8 mode not met
Maximum V4 mode time exceeded
Engine oil aeration present
Decel fuel cutoff active
Fuel shut-off timer active
Minimum heater temp low, HVAC system
Reduced engine power active, electronic throttle control
Brake torque management active
Axle torque limiting active
Engine metal over temperature protection active
Catalytic converter over temperature protection active
Piston protection active, knock detected
Hot coolant mode active
Engine over speed protection active
Fault Active or Fault Pending--cylinder deactivation is disabled for the following faults:
- Manifold Absolute Pressure Sensor
- Engine Oil Pressure Sensor
- Engine Coolant Temperature Sensor
- Vehicle Speed Sensor
- Crankshaft Position Sensor
- Engine Misfire Detected
- Cylinder Deactivation Solenoid Driver Circuit

The scan tool output control is used to deactivate half of the engine cylinders, V4 mode, by commanding all of the solenoids ON, or deactivate one cylinder switching to a V7 mode, by commanding ON one solenoid. Listed below are the powertrain conditions that will inhibit V4 mode, or V7 mode, with the engine running, while using the scan tool output control function:

Engine speed out of range
Manifold absolute pressure (MAP) sensor fault
Accelerator pedal position too high, electronic throttle control
Piston protection active, knock detected
Engine oil temperature out of range
Engine oil pressure out of range
Engine oil aeration present
Engine metal over temperature protection active
Accelerator pedal position rate of increase too high, electronic throttle control
Cylinder deactivation solenoid driver circuit fault
Engine coolant temperature sensor fault
Catalytic converter over temperature protection active
Brake booster vacuum pressure low
Axle torque limiting active
Brake torque management active
Vehicle speed sensor fault
Engine coolant temperature too high
Engine not running
Vehicle speed not zero
Engine coolant temperature low
Reduced Engine Power Active, electronic throttle control
Transmission gear incorrect
Transmission range incorrect
Ignition voltage out of range
Maximum V4 mode time exceeded

Listed below are the powertrain conditions that will inhibit a cylinder deactivation solenoid from being energized, with the ignition ON and the engine OFF, while using the scan tool output control function:

Engine speed not zero
Vehicle speed not zero
Transmission not in park or neutral
Ignition voltage out of range

For the system description covering the hydraulic/mechanical system of cylinder deactivation, refer to Cylinder Deactivation (Active

Customer: replied 6 years ago.
Reply to gmtech4's Post: I know how it works, that's what I don't like. I want to disable it.. turn it off.. never to work again.
Expert:  gmtech4 replied 6 years ago.
then you know that it is controlled by the ECM,the document I gave you also has various systems that if fail will disable it ,other than that it is in the trucks programing ,sorry if I am not helping
Customer: replied 6 years ago.
I am still looking for a way to disable the system. If anyone finds an answer to my question let me know... I'll pay! I'm researching it myself.
Expert:  gmtech4 replied 6 years ago.
no one else will answer sir because it is controlled by programing,thats it I tried to help educate you but it did not work ,I am again sorry but it cannot be done -Rob-and programing is from GM and cannot be changed ,it is web based and only certain updates are available when we go in to do any programing,disabling is not going to be available,
Customer: replied 6 years ago.
Reply to gmtech4's Post: You know I agreed to pay for an answer. You have taken the money, that was agreed to be held as a good faith deposit for a satisfactory answer,and not given me anything but a smart ass reply. I understand that if no one else answers they are probally stumped as much as I am... but you know..
they aren trying to get paid for something they couldn't deliver.
I expect to be credited back the $30.00! And in the future it would be wise for you to understand what you are collecting payment for, although I believe that you knew exactly what you were doing!
Expert:  gmtech4 replied 6 years ago.
I never meant to give you a smart ass answer and you have not accepted and do not have to so I'm sorry but if you read that discription and operation,all lot of things will disable the AFM ,let the timer run out on the post and you don't have to pay ,good day

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