Andrew Markel discusses timing components, and how issues with the variable valve timing actuator can cause codes from misalignment. Sponsored by INA, a Schaeffler brand.
Video courtesy ImportCar.
In 2010, GM announced that most LS V8 engines would be equipped with variable valve timing (VVT). Before this, VVT had already been available on GM’s small-block 6.0L and 6.2L V8s. GM did not ditch the pushrods and the camshaft in the block for the new model. Instead, they put a very sophisticated actuator on the end of the camshaft.
The CMP actuator system controls the amount of intake and exhaust valve overlap. The engine control module (ECM) can only command the CMP actuator to advance the valve timing from the park position or retard the valve timing back to the park position.
The camshaft has an internal oil passage that carries pressurized oil to the CMP actuator. Pressurized engine oil enters the camshaft at the second bearing journal oil galley.
The oil from the camshaft travels through a check valve and then a filter. The check valve keeps oil in the system after the engine is turned off. The oil then enters a spool valve that controls the flow to the CMP vanes in the actuator. Oil exits the valve and travels within the internal passages of the camshaft into the entry ports of the actuator.
The spool valve’s position is controlled by magnets and the ECM. When the spool is moved to the proper position, oil flow is directed through the valve and into the CMP actuator assembly. The CMP solenoid valve is a torque-to-yield design and should be replaced each time it is removed.
The CMP actuator magnet is located in the engine front cover and is sealed by a press-in-place gasket. The CMP actuator magnet is controlled by a 12-volt 150 Hz pulse width 0-100 percent duty-cycle signal from the ECM. When energized, the solenoid uses electromagnetic force on the magnet pintle to position the spool valve of the CMP solenoid valve.
The CMP actuator is a vane-type design that hydraulically changes angle or timing of the camshaft relative to crankshaft position. The CMP actuator allows earlier or later intake and exhaust valve opening. The CMP actuator cannot vary the duration of valve opening or valve lift. The CMP actuator is to be serviced as an assembly.
The CMP actuator consists of:
Do not push or pull on the reluctor wheel of the CMP actuator during removal or installation. The reluctor wheel is retained to the front of the CMP actuator by three roll pins. Pushing or pulling on the wheel may dislodge the wheel from the front of the actuator. The actuator return spring is under tension and may rotate the dislodged reluctor wheel, causing personal injury.
A CMP actuator dynamically changes valve timing events relative to piston timing by controlling camshaft position. This is sometimes referred to as variable valve timing or camshaft phasing.
There are five cavities divided by vanes within the CMP actuator. When oil is directed to the advance cavities, the camshaft timing is advanced. When oil is directed to the retard cavities, the camshaft timing is retarded. When oil is directed to both cavities, the camshaft is held stationary.
The CMP actuator has a 52 degree range of movement at the camshaft (later models have 62 degree range of movement). With the engine not running and no engine oil pressure to the CMP actuator, the high-tension spring positions camshaft timing at the 7 degree advanced park position at the crankshaft (3.5 degrees at the camshaft).
During normal engine operation, and based on performance requirements, the ECM may adjust camshaft timing as required within a range from 7 degrees advanced at the crankshaft (3.5 degrees at the camshaft) to 55 degrees retard at the crankshaft (27.5 degrees at the camshaft).
The valve may also, under certain conditions, be positioned in a neutral position with alternating low, balanced oil flow between the advance and retard passages of the actuator.
Oil flows from the camshaft into the valve inlet #3 through the internal check ball and filter.
Oil exits the valve #2 and travels within the internal passages of the camshaft into the entry ports #7 of the actuator.
The center oil groove of the actuator is pressurized and oil reenters the valve #1.
Valve spool position directs oil out of the valve advance #5 or retard #4 ports to the actuator.
The valve may also, under certain conditions, be positioned in a neutral position with alternating low, balanced oil flow between the advance and retard passages of the actuator.
One of the ways automakers squeeze more horsepower and torque from an engine is adding variable valve timing (VVT) to the valvetrain. A conventional camshaft has fixed valve lift, duration and timing, so the grind is always a compromise between fuel economy, performance and emissions. But with cam phasing VVT, duration, valve overlap and timing can be changed on the go to optimize engine performance at different RPMs, loads and operating conditions.
Cam phasing systems essentially rotate the camshaft fore or aft to advance or retard timing. This differs from other VVT systems such as Honda’s VTEC and Nissan’s VVL that are “cam changing” systems. In a cam changing VVT system, the position of the rocker arms changes when oil pressure is applied so the rockers will follow a different set of lobes on the cam for increased lift, duration and power.
Some applications combine both cam phasing and cam changing such as Audi’s Valvelift, BMW’s VANOS, Honda’s i-VTEC, Mercedes’ Camtronic, Porsche’s Variocam Plus and Toyota’s VVTL-i.
Some applications also have the ability to continuously vary valve lift on the go, such as BMW’s Valvetronic, Nissan’s CVTC and VVEL and Toyota’s Valvematic. For this article, we’re limiting our discussion to applications that use some type of cam phasing to change valve timing.
Valve timing can be advanced at low RPMs for better throttle response and torque. Valve duration can be increased at higher engine speeds to improve breathing and power. Valve timing can also be retarded when the engine is under load to reduce NOx emissions (and eliminate the need for an EGR valve).
On DOHC engines with separate cam phasers for the intake and exhaust cams, the powertrain control module can independently advance or retard the intake and exhaust cams. This changes the centerline between the cams and the lobe separation angle, which, in turn, changes valve overlap and duration. On SOHC and pushrod engines that have VVT, the same cam operates both the intake and exhaust valves, so advancing or retarding the cam simultaneously changes both the intake and exhaust timing.
Most of the VVT systems you are likely to encounter are those with hydraulically actuated cam phasers, although a few (such as Lexus) use an electric actuator to advance or retard cam timing. The cam phaser changes camshaft and valve timing by rotating the relative position of the camshaft slightly fore or aft compared to its normal base timing setting. The phaser is part of the cam drive system and is mounted on the cam drive gear or sprocket.
There are several basic designs:
• Helical gear phasers. These are used on many of the older applications and are essentially “on” or “off” actuators. When oil pressure is applied to the gear mechanism inside the phaser, it forces the helical gear to move. This typically retards cam timing 20 to 30 degrees. A spring then returns the cam back to its normal position when oil pressure is relieved.
• Lobed rotor phasers. With this design, the phaser housing usually has four chambers with a movable four-lobed rotor inside. When oil pressure is routed into the chambers, it pushes the lobed rotor one way or the other to advance or retard cam timing. Many of these units provide incremental timing changes that can vary from zero degrees of advance or retard, up to full advance or retard. Timing changes can range from 20 degrees to as much as 60 degrees on some applications.
• Vane rotor phasers. They function pretty much the same as a lobed rotor phaser by offering incremental timing advance or retard as oil pressure is applied to the chambers on either side of the vanes. The phaser usually has five vanes that protrude outward from the rotor, with each vane being located within its own oil cavity.
With lobed- and vane-style phasers, there is an internal dowel pin that holds the rotor in the base timing position when no oil pressure is applied. This prevents rotor movement and noise when the engine is started and when it is idling. When oil pressure is applied to the phaser, it pushes the dowel pin out of its locating hole and allows the rotor to move.
Most VVT systems are not engaged when the engine is idling and remain in the locked or base timing setting. With hydraulically actuated cam phasers, the VVT system is also usually not active until the engine reaches normal operating temperature. As engine speed and/or load change, the PCM looks at its various sensor inputs and commands the oil flow control valve solenoids to open. They are located near the phasers on the timing cover or valve covers.
When the solenoid valve opens, oil pressure is routed to the phaser and cam timing is advanced or retarded depending on the design of the phaser and oil control valve. This is also affected by how the oil pressure is routed in the chambers inside the phaser. On applications that offer incremental changes in cam timing, the oil flow control valve is pulse-width modulated. Changing the duty cycle of the solenoid controls oil flow through the phaser and determines how much cam timing is advanced or retarded.
As simple as it all sounds, any number of things may set a VVT-related fault code:
• Electrical problems with the cam position (CMP) sensor. The PCM has to receive an accurate cam position signal to monitor the operation of the VVT system. If the sensor has failed or is not reading accurately, it can set a camshaft position error fault code.
Cam position sensors may be magnetic or of the Hall effect variety. You can check the resistance of a magnetic sensor by back-probing with an ohmmeter (usually 500 to 900 ohms). A magnetic sensor should also produce an AC output of at least 20 mV at idle, which you can see on a scope or a scan tool that can graph voltage signals.
Hall effect sensors produce a digital signal that you can check on a scope or a scan tool that can display sensor data. The output should be an on-off square waveform. If the vehicle also provides a cam position PID and your scan tool can read it, check the value to see if it makes sense and changes with RPM and/or load.
• Electrical problems with the voltage supply, ground connection or wiring harness to the oil flow control solenoid(s). If a solenoid fails to open and close when commanded to do so, it will prevent oil pressure from reaching the cam phaser. This will also set a camshaft position error fault code.
• Low oil pressure due to a low oil level in the crankcase, worn oil pump, worn main bearings or worn cam bearings. Hydraulically actuated cam phasers require good oil pressure to change their position. If they don’t get it, cam timing won’t change. Check the oil level in the crankcase, and, if it is low, add oil and check for oil leaks. If adding oil doesn’t remedy the situation, the phasers may not be receiving adequate oil pressure due to the other conditions just mentioned.
Connect an oil pressure gauge to the oil sending unit port and see if oil pressure is within specs. If it isn’t, the engine has internal problems that will need to be corrected. Sometimes, replacing the stock oil pump with a high-volume oil pump will correct a VVT cam phaser issue if the problem is insufficient oil flow to the cam and upper valvetrain.
• Using the wrong viscosity motor oil. Most late-model engines specify low-viscosity oils such as 5W-20 or 0W-20. Using a heavier, multi-viscosity oil such as 10W-30 may slow down the response of the cam phaser and set a fault code.
• Not changing the oil often enough may allow sludge to build up inside the phasers. This may make the phasers slow to respond to timing change commands or to even stick in a fixed position.
• Debris, sludge or varnish can restrict or block the oil flow control valve or cam phaser inlet screens, preventing the phasers from working properly.
• Using the wrong oil viscosity in the engine may also make the cam phasers slow to respond, causing a camshaft position fault code to be set.
• Physical wear or damage inside the cam phaser housing may prevent it from rotating, cause it to stick or make the unit noisy. A broken return spring may prevent it from returning to base timing.
Think of a lobed- or vane-style cam phaser as a backward-operating gerotor-style oil pump. A gerotor oil pump produces oil pressure as the pump rotates. By comparison, a cam phaser rotates when oil pressure is applied to the rotor. Because of this, the clearances between the housing and rotor have to be fairly tight; otherwise, a loss of internal pressure will adversely affect the operation of the unit.
With lobed rotor and vane-style cam phasers, wear in the phaser housing, vanes or lobes reduces the unit’s ability to hold pressure and function normally. The dowel pin that holds the rotor in its neutral position may also become worn or shear off. The hole that the pin fits into may also become elongated or worn, preventing it from holding base timing. This can make the phaser noisy at idle, as well as cause erratic valve timing.
Cam phasers are expensive units to replace, costing anywhere from $100 to nearly $300 each depending on the application. Various aftermarket suppliers have replacement cam phasers in their product lines, which now include many popular import applications, such as Audi, BMW, Honda, Lexus, Mazda, Mercedes, Mitsubishi, Nissan, Porsche, Toyota, Volkswagen and Volvo.
Although some techs have tried rebuilding worn or damaged cam phasers, the OEMs treat them as a sealed unit, so no internal replacement parts or repair kits are available. Consequently, if you discover a bad cam phaser on a customer’s vehicle, you have to replace it.
On high-mileage engines, replacing the timing chain(s) and guides/tensioners is also recommended if you are replacing a bad cam phaser.
Note: If the upper valvetrain on the engine has a buildup of sludge, the engine should be flushed and the oil changed before the vehicle is returned to the customer. Use the recommended oil viscosity because using oil that is too thick may prevent the cam phasers from reacting quickly enough when commanded to change timing. This could cause a CEL and a VVT-related code to be set. Also, stress the importance of regular oil changes to your customers. Clean oil is essential for smooth operation of the VVT system on any engine.
Several import vehicles have had problems with their variable valve timing systems. These include:
• BMW had to recall about 156,000 cars including 2010-’12 model year 1 Series, 3 Series, 5 Series, X3, X5 , X6 and Z4 vehicles for a possible issue with the camshaft gear bolts that attach the variable valve timing VANOS cam phaser housing to the intake and exhaust cams. The bolts may work loose or break, causing the Check Engine light to come on, a sudden loss of power, engine noise, stalling and/or engine damage. If the original bolts are loose or broken, BMW recommends replacing the VANOS cam phaser unit and installing new bolts. The recall campaign number is 14V-176, issued October 2014 for N51, N52K and N52T engines. New bolts should be tightened to 9 Nm, then angle torqued 60 degrees.
• Mazda’s 2007-’10 CX-7 2.3L turbo, 2007-’10 Mazdaspeed3 and 2006-’07 Mazdaspeed6 have had some problems with loud ticking noises coming from the engine’s VVT system upon initial startup. The noise is caused by the cam phaser lock pin not being able to fully engage. Mazda TSB 01-012/12 issued April 3, 2012 says the loud ticking noise can also be due to a stretched timing chain. They recommend inspecting the timing chain and cam phaser to determine which is causing the noise since either one could be the cause. If the engine is noisy only on initial startup then quiets down, the cause is the cam phaser. If the engine continues to make noise from the timing cover area after it has warmed up, the cause is likely a stretched timing chain.
• Lexus issued a recall on September 4, 2013 for 2006-’11 IS350 models, 2010-’11 IS350C models and 2007-’11 GS350 models for a cam phaser sprocket housing bolt issue. The bolts on the intake cam phaser sprocket may come loose, causing the phaser sprocket to separate from the cam. A lock pin inside the phaser is supposed to hold the inner rotor to the outer rotor when the engine is first started. If this fails to occur, the inner rotor can slam against the outer rotor, causing the bolts to loosen over time. The fix is to replace the intake cam phaser. The exhaust cam phaser is not affected because it is a different design. Recommended torque for the new intake cam phaser bolts is 100 Nm (74 ft. lbs.).
Article courtesy ImportCar.
Variable valve timing is becoming a standard system on most late-model engines because it offers higher performance from a smaller displacement engine at higher rpms. Oil plays a larger role in VVT systems. They need engine oil not only for lubrication, but also to actuate the camshafts to change the profile of the lobes.
Oil quality, condition and specifications are critical to the performance of the system. The passages and orifices can be very small and prone to sludging. Also, the oil acts as hydraulic fluid to move the actuators. If the oil does not have the correct viscosity, the behavior of the actuators will change.
These systems are simple to work with from a diagnostic perspective. Most VVT components are non-serviceable and have integrated sensors, but they are part of a larger diagnostic picture that includes everything from the throttle body to the oxygen sensors.
The two most common codes I’ve run across are P0011 and P0021, camshaft position sensor “bank 1” and camshaft position sensor “bank 2,” respectively. These codes (like any code) don’t necessarily mean the sensor is faulty, but the diagnostic charts will tell you to look at the VVT system for a fault and check the sensor as well. Some of the common areas to inspect: valve timing, oil control valve, oil control valve filter screen, camshaft timing/gears and the electrical side of the operation as well as the PCM.
The very first step I take before turning nuts and bolts is to check the oil. Dirty oil and the lack of regular oil changes can leave a buildup of sludge or debris in the passages leading to the pressure control valve that operates the VVT. If the oil is dirty and too much sludge accumulates at the valve ports, the sludge can be passed on through the cam and the valve assembly. From there, the oil passages in the cam can be compromised and could result in a cam failure due to scored journals.
Keep in mind that the VVT system is not operated at a normal driving condition rpm. For example, the Honda VTEC system doesn’t operate below 4,500 rpm. So, if you have someone who never gets the car out on the highway and never changes the oil, there is a potential problem waiting to happen when the car is revved up above 4,500 rpm on its next highway trip.
Lack of regular maintenance seems to be the big factor in most of these systems. Unlike vehicles from years gone by where certain maintenance issues could be neglected, these newer engines and newer systems require the utmost in care. Stressing this point to your customers and performing the required basic maintenance per the manufacturer’s schedule will safeguard their vehicle and increase your profits.
Code P0521 (oil pressure sensor/switch range/performance) could be an indication of the quality of the engine oil. This might not be the best diagnostic answer, but when I’ve seen this code on several vehicles, the oil was black and neglected. In some cases, the code can also indicate that the wrong type of oil has been used. I wouldn’t use this as the final solution to the VVT problem, but as an indication of things to come.
Most late-model engines are factory filled with multiviscosity 5w-20 or 5w-30 motor oil, but some require 5w-40, 0w-20 or 0w-30. Be sure to follow the viscosity recommendations because many of these engines have tighter bearing clearances that require a lower-viscosity oil for proper lubrication. Thinner oils also improve fuel economy. In some applications, such as the Toyota Prius, using the wrong viscosity oil (too heavy) may set a fault code. On others, an oil that is too heavy may interfere with the normal operation of the VVT system, causing additional fault codes to set.
Fortunately, the European and Asian vehicle manufacturers also use the same SAE viscosity ratings as their domestic counterparts, which makes life easier when it comes to choosing an oil that meets a specified viscosity recommendation. The trouble is, not all motor oils actually meet the viscosity ratings that are claimed on the product — and the situation is even worse with bulk oils.
According to a recent API survey of more than 1,800 oil samples purchased from bulk dispenser tanks in quick lube shops across the U.S., nearly 20% (one out of five!) failed to meet API standards. Either the viscosity was incorrect or the additive package failed to meet the claimed performance level.
You should be able to find out which oils are approved for various makes/models/applications by searching the OEM service literature or an aftermarket repair database. Audi and VW have TSBs that cover this subject, but we couldn’t locate similar information from BMW or Mercedes (they may have it, but we couldn’t find it). BMW says it requires its own BMW Long Life 4 motor oil (such as 5w-30, P/N 07510017866), but it doesn’t say what other brands meet its specs.
Once a vehicle is out of warranty, any type of oil can be used provided it meets the vehicle manufacturer’s viscosity recommendations and basic performance requirements. Use the wrong oil, such as a bargain-priced conventional oil in an engine that requires a high-quality, long-life synthetic, and the results could be engine damage or failure.
Courtesy Underhood Service.