Compass 4WD L4-2.4L VIN W (2007)
key-on. The cleaning strategy is known as "debris crush mode". At key-on the GPEC1 cycles the oil control valve on and off several (5) times to crush
any debris in the oil control valve and prevent the spool valve from sticking. In non operating condition, the camshaft stays in lockpin position of cam
phases. This is 120 degrees ATDC for intake camshaft and 120 degrees BTDC for exhaust camshaft.
There are two oil control valves. One valve directs oil to the intake cam phaser, the other valve directs oil to the exhaust cam phaser. The valves are
designed and function in the same manner. The outer casing of each oil valve has five oil passages. A passage for pressurized supply oil. A passage to
the advance chamber of the cam phaser. A passage to the retard chamber of the cam phaser. A passage for oil return from the advance chamber of the
cam phaser. A passage for oil return from the retard chamber of the cam phaser. Oil flows through the passages and applies pressure to the cam phasers
to change cam timing.
There are two cam phasers. One phaser controls the position of the intake camshaft. The other phaser controls the position of the exhaust camshaft. The
phasers consist of a sprocket, a rotor vane, and a housing or stator. The exhaust cam phaser also consists of a front bushing and spring. We will discuss
the purpose and function of the bushing and spring later. The housing is bolted and permanently fixed to the camshaft sprocket, while the rotor vane is
bolted and permanently fixed to the camshaft. With this design, any movement of the rotor vane in relation to the housing will also move the camshaft.
The phaser and sprocket are serviced as an assembly.
Camshaft and crankshaft sensors provide feedback to the GPEC1 regarding the actual position of the camshafts. The GPEC1 then compares the actual
camshaft positioning with desired positioning. If the desired positioning is not achieved within a specified time, during the second key cycle a trouble
code is set.
There are six new diagnostic trouble codes available to help you determine if the control circuit from the GPEC1 to the oil control valve is intact and
operating properly. The codes identify whether the control circuit is open, shorted to ground, or shorted to power. Three trouble codes are related to
intake camshaft positioning, the other three codes are specific to exhaust camshaft positioning.
The oil control valve contains both electrical and mechanical components. It is electrically controlled by the GPEC1. The electrical current that energizes
the coil results in mechanical motion of the spool valve. It is possible to verify both the electrical and mechanical operation of the valve. The oil control
valve consists of a coil that is energized to move a spool within an outer casing. The condition of the coil can be tested with a Digital Volt Ohmmeter or
DVOM. With the DVOM set to measure resistance, check the coil for an open, a short to ground, or excessive resistance. The correct resistance value of
the coil is between 6 and 8 ohms. The mechanical operation of the oil control valve can be tested using actuator commands on the scan tool. Remove
the oil control valve, then navigate to the actuator menu and select the oil control valve. Use commands to activate the valve and watch as the spool valve
moves back and forth inside the casing.
Because the cam phasers are hydraulically operated by engine oil, the condition of the oil is very important. The oil must be of the correct viscosity, not
obstructed by debris, to maintain correct pressure. Maintaining the correct oil viscosity is critical to the operation of the variable valve timing system.
The wrong oil viscosity may cause the variable valve timing to malfunction and trouble codes to set. The correct oil viscosity for this system is 5W20.
Oil must be clean, unobstructed and free to flow through the variable valve timing system. Oil could become obstructed in oil passages located in the
cylinder head, cylinder block, or even in the oil screen. In the event oil flow is obstructed, further diagnosis or disassembly may be required to pin point
the source of the obstruction. The variable valve timing system relies on oil pressure to advance or retard the position of the camshaft. Insufficient oil
pressure will adversely affect the operation of variable valve timing. The minimum oil pressure for this system is 15 psi at normal operating temperature.
Though not directly used to change camshaft positioning, the oil screen is an important component of the variable valve timing system. It helps to
remove debris going to the variable valve timing components. The oil screen is located in the cylinder block, immediately below the cylinder head. Oil
must pass through the oil screen before entering the oil control valve. The cylinder head must be removed to service the oil screen. The intention is not to
service the oil screen during vehicle life.
How the cam phaser works. The cam phaser assembly has eight separate chambers; four advance chambers and four retard chambers. When camshaft
advance is requested, oil enters all four advance chambers and exerts force on the rotor vane. Because the rotor vane is bolted to the camshaft, the entire
camshaft profile moves along with the rotor vane. At the same time, oil is forced out of the retard chambers. When camshaft retard is requested oil enters
the retard chambers to move the camshaft in the opposite direction. There is a lock pin on one side of the rotor vane that fits inside a recessed area in the
housing. The lock pin ensures that the default position of the intake cam phaser is 120 crankshaft degrees full retard and the default position of the
exhaust cam phaser is 120 crankshaft degrees full advance. When the engine is turned off, rotational force and inertia move the intake camshaft and rotor
vane toward the retard position. The exhaust cam phaser includes a spring and bushing to work against the rotational force of the engine, allowing the
exhaust cam phaser to lock in the fully advanced position. Under most conditions the cam phasers are returned to lock pin position when the engine is
turned off. In the unique condition of an engine stall, which abruptly shuts off the engine, the cam phasers may not return to the lock pin position. In this
case, the phasers will return to the lock pin position at the next start-up. Lock pin position is the most ideal cam timing for idle stability. When engine
rpm exceeds approximately 600 to 1000 rpm, oil pressure unlocks the pins and variable valve timing resumes. Once enabling conditions are met, the
GPEC1 uses input from sensors to calculate optimum valve timing.
There are four preprogrammed modes from which the GPEC1 bases initial valve timing.
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Starting
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Idle or Part throttle
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Wide open throttle
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Limp-in or Default
From each preprogrammed mode, the GPEC1 adjusts valve timing based on operating conditions.
