Timing is Everything
I’m working on a 2013 Subaru Forester, with the 2.5l FB engine. The engine has developed an oil leak, which I have determined is coming from the area around an oil control solenoid valve (OCV), on the left bank of the engine. The engine management system has also stored a DTC related to the operation of the engine’s variable valve timing system. I think the DTC may have been caused by the leaking OCV and engine oil getting into the harness. The OCV isn’t terribly expensive, but I don’t want to replace it if something more serious is going on. Also, since the engine has variable valve timing on both banks of the Forester’s flat-four engine, I’m wondering if I should replace the OCV on the other bank, even though it’s not leaking at this time.
St. Louis, MO
In the early 2000s, Subaru released its first variable camshaft timing system, called the Active Valve Control System (AVCS). The system was originally introduced to improve engine torque, reduce emissions and improve the driveability of the company’s then-current EJ-series engines. AVCS is a PCM-controlled, hydraulically actuated, adjustable camshaft gear. With the ability to advance or retard the camshaft timing, Subaru engineers were no longer constrained by a single camshaft profile. AVCS allows the PCM to alter the moment the valves opened relative to engine load. This can improve engine power, improve fuel economy and reduce emissions. Valve lift is not controlled by AVCS.
AVCS has been offered in two flavors. Single AVCS (S-AVCS) adjusts the valve timingof only the intake camshafts; dual AVCS (D-AVCS) adjusts the valve timing of both the intake and exhaust camshafts. Camshaft adjustments on D-AVCS systems can also be made independent of each other. Not surprisingly, D-AVCS systems are found on engines with dual overhead camshafts, typically also with turbochargers and higher performance specifications. The Impreza WRX STi and BRZ are two examples of recent Subaru models equipped with D-AVCS.
The PCM uses sensor data such as throttle position, coolant temperature, intake air and camshaft position to determine the optimal amount of cam phasing. The PCM then sends a signal to the oil control valve, which regulates oil flow into the actuator. The high oil pressure then enters the camshaft actuator to adjust cam angle by rotating the interior rotor. This causes the camshaft to rotate to either an advanced or retarded position.
At idle the AVCS system is inactive and provides no advance or retard. A smooth idle results from minimal valve overlap, which also promotes stability in the chamber by opening the intake valve after top dead center (ATDC). At low to moderate engine load, an S-AVCS system will begin to advance the intake camshaft. As the rotor advances, it opens the intake valves sooner, which causes reversion of exhaust gases into the intake manifold. This cools the combustion chamber by reducing the energy of the next combustion cycle, thus reducing NOx formation. Opening the intake valves early means they also close sooner. This creates a higher dynamic compression ratio, which improves torque production, fuel economy and turbo response (if so equipped).
At full load, the AVCS system reaches full advance in the midrange and slowly reduces the amount of advance as engine rpm rises toward the rev limit. At full advance, the chamber begins to see a weak scavenging effect due to exhaust pulse timing. The early valve closing also produces significantly higher dynamic compression, which helps torque productionbut can increase the chance of detonation.
D-AVCS systems allow the PCM to adjust the intake and exhaust camshafts independently. This offers advantages over S-AVCS, such as: increased fuel economy and reduced emissions (EGR effect), increased low to midrange torque and increased overlap moment duration and effect. At cruising and non-WOT conditions, the exhaust cam timing can be retarded, which induces an EGR effect in certain rpm ranges. This reduces emissions, cools the combustion temperature, slows the burn rate and improves fuel economy by reducing the amount of air/fuel mixture that enters the chamber.
By allowing both intake and exhaust valve timing to be adjusted on demand, the D-AVCS system gives engineers the ability to design camshaft profiles that are more suitable to a certain rpm range. The AVCS is then used to widen the torque plateau or improve performance elsewhere.
The oil control valves (OCVs), which direct the oil flow that allows the AVCS system to function, have been a source of difficulty, as you’ve discovered. Engine oil may leak from an OCV and find its way into the OCV harness connector. Over time, this oil leakage may cause the Check Engine light to illuminate, and various AVCS-related DTCs to be stored in memory.
A new OCV, with a redesigned internal oil seal, was added to vehicle production a few years ago. Three different OCVs have been used for different applications. Check with your parts supplier to determine which OCV is appropriate for your application.
If you don’t know a vehicle’s service history, it may be difficult to immediately determine whether it has a new or an old OCV installed. They’re externally identical, but the newer OCV design can be visually identified by the production lot number located on the face of the solenoid. The 11-digit number identifies a production date stamp “YYDDDHHMMTS.” OCVs having a date stamp with the first fivedigits as 17159****** or higher (159th day of 2017) are new parts.
If oil is found in the harness connector during diagnosis of AVCSrelated DTCs, replace the affected OCV with a new part. Follow the service procedures as outlined in the applicable Service Manual.
There have been reports involving engine oil “wicking” past the OCV engine harness connector and into the related wiring harnesses and connectors. If any part of the engine wiring harnesses and/or connectors are contaminated, try degreasing the affected components using a spray parts cleaner. If you’re unable to remove the contamination, the harness itself may also need to be replaced. Additional information on this topic can be found in Subaru TSB No. 02-170-17R.
You may remember similar problems involving engine coolant on vehicles from other manufacturers. At that time, the phenomenon was referred to as a “capillary action,” which allowed engine coolant to travel all the way from a leaking engine coolant temperature sensor, through a vehicle’s wiring harness, to the PCM. In extreme cases, if coolant reached and penetrated the PCM, that component could be irreparably damaged as well.
The Subaru TSB doesn’t make any reference to PCM damage, and engine oil may not be able to travel through the wiring harness quite as easily (or as far) as coolant. A leaking OCV and the resulting wicking or capillary action can be signaled by oily spots on the wiring harness’ protective outer wrapping and inside harness connectors. If you want to reassure yourself that the oil hasn’t traveled far enough to cause further damage, consult a wiring diagram to identify junction points where harness connectors are used. Unplug these harness connectors, check for oil inside and clean as necessary. Your last stop should be the main harness connectors at the PCM. If you can get everything cleaned up after replacing the leaking OCV, the drastic (and expensive) step of a harness replacement recommended by the TSB may be averted. Good luck.