Wrap-Up

Ready for Review

• Variable valve timing (VVT) is used to increase performance and decrease emissions from an internal combustion engine (ICE).
• The valve timing is controlled by the powertrain control module (PCM) and the timing component on the engine.
• VVT is controlled differently by different OEMs.
• The BMW VANOS system uses piston assembly that has a splined drive gear that slides into the camshaft to advance the camshaft. When it is removed, the camshaft will return to previous position because of the helical cut gears.
• Toyota VVT-iE VVT is controlled by an electric motor that changes the position of the camshaft by rotating the electric motor to the requested position.
• The Toyota system is independent of oil level or pressure, which means it works properly regardless of the oil situation.
• If there is a VVT issue and the oil pressure is questionable, the oil pressure to verify that it has enough to sustain the engine and VVT operation must be checked.
• Simple electrical testing on oil control valve (OCV) can quickly narrow down the source of the failure of the VVT system.
• A digital storage oscilloscope (DSO) is used to watch the operation of the OCV and compare that to the actual output on the engine to validate the operation of the VVT components.
• There are three actuator/phaser designs: helical, vane, and lobed. The most commonly used design is the vane type.
• The phaser is controlled through an OCV, which can be either electrically controlled or magnetically controlled.
• Variable displacement engines can convert a V8 engine to a V4 engine instantaneously to improve fuel economy and decrease emissions.
• This technology can also be applied to smaller engines, such as the Audi Valvelift system, which slides a camshaft tube to take over valve operations.
• Mercedes Camtronic uses an electric motor to pivot the rocker arm to either open the valve fully or not open it at all.
• Honda VTEC valve control system uses a hydraulically actuated lock pin to lock the valve rocker arms to a third rocker arm that is operating on a more aggressive cam profile.
• All of the valve lift control systems are heavily integrated with all of the other systems of the vehicle so that operation is seamless and as efficient as possible.
• Before beginning to diagnose VVT/VVL systems, the base engine timing must be verified and the oil level must be validated.
• VVT/VVL noise may be related to component failure or engine dysfunction because of a biased sensor.
• Verifying the cam-to-crank relationship with the CMP sensor and CKP sensor will help determine whether there is a mechanical issue with the timing components.

Key Terms

active fuel management (AFM)  A General Motors cylinder deactivation system that collapses valve lifters to shut off cylinders.

active noise control (ANC)  An Audi noise control system employed on its Valvelift system to mitigate the noises created by disabling cylinders.

BMW VANOS (variable nockenwellen steuerung)  VVT from BMW that first appeared in 1992. The first version controlled only the intake camshaft. In 1996, dual VANOS was introduced, which controlled both camshafts. This is an oil-fed system that is electronically controlled to increase performance and decrease emissions.

helical phaser  A type of phaser that has the gear teeth cut at an angle so that as the collar is pushed out, the inner gear, which is connected to the camshaft, rotates, thus rotating the camshaft. A splined phaser is oil fed, so the oil must be up to the recommended level.

Honda VTEC (variable valve timing and lift electronic control)  An oil-operated system, similar to VVT, that slides a pin to connect both rocker arms on one cylinder to a third rocker arm that is operating on a more aggressive duration. This system allows for the use of two different camshaft lobe designs on the same engine so that it can adapt to the needs of the driver.

Mercedes Camtronic  This system adjusts the intake valve lift based on engine load. Lift is changed mechanically by input of an electric motor controlled by the PCM.

multiple displacement system (MDS)  A Chrysler cylinder deactivation system employed on the Hemi engine family. This system limits the oil flow to four predetermined cylinders lifters, which allows them to collapse while turning off the ignition coil and injector to turn a V8 into a V4 engine.

oil control valve (OCV)  An electric solenoid that controls oil flow to the phaser on a valve train, which is controlled by the engine’s PCM.

Toyota VVT-iE (variable valve timing with intelligence by electric motor)  A system controlled by an electric motor on the end of the camshaft. By using an electric motor, low oil level or pressure doesn’t affect system performance.

vane-type phaser  A type of phaser that operates with a set of paddles inside the assembly. When oil pressure is applied to one side of the paddles, it rotates the camshaft inside the phaser; to reverse the rotation, it applies oil pressure to the opposite side of the paddles.

variable displacement engine (VDS)  An engine that can change the volume (cubic inches or liters) of displacement through cylinder deactivation or a mechanical means.

variable valve lift (VVL)  A system employed on an engine to change the amount of lift of the valve based on input from the PCM.

variable valve timing (VVT)  The ability of an engine to change the advance or retard of a camshaft or camshafts to match the requirements of the engine performance level.

Review Questions

1. The variable valve timing (VVT) system on an engine controls what part of the timing?
   • The advance position or retarded position of the crankshaft.
   • The advance position or retarded position of the camshaft.
   • The PCM view of the engine timing.
   • The ignition timing of the engine.
2. A vane phaser has what part below that is different from a helical or spline drive phaser?
   • Return springs.
   • Oil control valve (OCV).
   • Rotor attached to the camshaft.
   • Camshaft with oil passages drilled in it.
3. When diagnosing a VVT fault, the first step is to check ___________.
   • the coolant level
   • the air filter
   • the battery capacity
   • the engine oil level
4. All of these statements are true except:
   • Most VVT systems rotate the camshaft to affect the advance or retard of the valve events.
   • On the Toyota VVT-iE system, the camshaft is rotated with an electric motor.
   • VVT is used to decrease wear on the engine as it decreases the performance of the engine to maintain the engine.
   • Cylinder deactivation on a GM product is controlled with a LOMA.
5. The magnetically controlled phaser has a permanent magnet (PM) that operates the system.
   • True.
   • False.
6. A camshaft position (CMP) or crankshaft position (CKP) correlation code in the PCM can do what to the VVT system?
   • Nothing; they are independent systems.
   • It could disable it because it thinks there is a timing issue with the engine.
   • Those codes could cause the system to adapt to the situation, so the engine could continue to operate.
   • Cause the system to operate all the time to try and correct the situation.
7. Normal timing chain and timing belt replacement should be undertaken at the required times; otherwise, failure could cause ____________.
   • the engine to operate as designed
   • nothing, because an engine with VVT will overcome a timing component failure
   • increased engine performance
   • timing to become out of alignment, causing the engine to operate incorrectly or not at all
8. When replacing the camshaft phaser, the technician should ______________.
   • disassemble it and replace the broken components inside the phaser
   • replace the phaser as a complete unit
   • replace the engine because phasers are not replaceable
   • also replace the camshaft because it is most likely also damaged
9. The Honda VTEC system uses multiple rocker arms to facilitate the change of intake camshaft profiles. How does the PCM make the change as the engine is operating?
   • It uses oil pressure to move a pin to lock the third rocker arm to the other two.
   • The PCM uses an electric motor to physically lock all three together.
   • The engine automatically mechanically locks all three rocker arms together.
   • The VTEC module kicks in the rocker arm operation.
10. When diagnosing an intermittent electrical fault in the VVT system, after checking the engine oil level, the technician should look at what component that controls the operation of the system?
    • Spark plugs.
    • CKP sensor.
    • CMP sensor.
    • OCV.

ASE Technician A/Technician B–Style Questions

1. Technician A says Audi’s Valvelift system uses sliding camshaft tubes to change the lift of the rocker arm. Technician B says that when conducting timing chain replacement, replacing only the chain is recommended. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says that low oil level does not affect a VVT system that uses oil to operate the cam phasers. Technician B says a Chrysler multiple displacement system (MDS) controls oil flow designated lifters, which it can collapse to disable cylinders on the engine. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says that when changing the timing belt, retiming the phaser to the crankshaft must be performed to allow the engine to operate correctly. Technician B says GM’s Active Fuel Management (AFM) system improves fuel economy by 18%. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says that improving fuel economy and performance and decreasing emissions is the purpose of VVT technology. Technician B says the Honda VTEC system uses a third lobe on the camshaft to operate the valves on in performance mode. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says the Mercedes Camtronic system uses an electric motor to pivot the rocker arm motion to open the valve either more or less. Technician B says to verify mechanical engine timing after diagnosing the VVT system. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says that by using the CMP/CKP sensor waveforms, the technician can determine whether the valve timing is off. Technician B says a helical phaser has a return spring that fails a lot and has led to the decreased usage of this type of phaser. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says the LOMA on an AFM engine has all the solenoids and an oil pressure sensor as part of it. Technician B that when testing for operational voltage in the system, the technician should refer to the wiring diagram. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says that when using a digital storage oscilloscope (DSO) to test the OCV, the waveform should be very jagged and drop out a lot. Technician B says that the base engine mechanical condition should be checked before condemning any other VVT components. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says magnetically actuated phasers use an OCV that responds to the electromagnet to control oil flow to the phaser. Technician B says increased usage of VVT/VVL systems will not happen because of the minimal gains. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says vane phasers have cavities that fill up with coolant to rotate the camshaft. Technician B says when resistance testing the OCV, the technician is looking for a complete circuit with approximately 8–15 ohms, but they should consult service information. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B