When the Check Engine light is on, it is normal for some other functions to be disabled, including Cruise Control, and this results in those lights coming on or flashing as well.
P0026 indicates a problem in the AVLS (Active Valve Lift System) on the right/passenger side of the engine. (A P0028 would be a left/driver side problem.)
The engine has two intake valves in each cylinder. At lower engine speeds, one does not lift (open) as much as the other, but at higher engine speeds. This changes the way the injected fuel circulates in the cylinder, reducing emissions at lower rpm but ensuring proper airflow into the cylinder at higher rpm.
The valve lift mechanism is hydraulically controlled. Oil coming from the engine oil pump (through the engine oil filter) is sent to the AVLS oil change solenoid. The output of the solenoid goes to the lift mechanism on the camshaft through an oil line. There is an oil pressure sensor switch in the oil line between the solenoid and the camshaft.
The solenoid is driven by a duty cycle (pulsing on-off) electrical signal. When the signal speed (duty cycle) is low, little oil passes through the solenoid and the line pressure is low. In this case, the single intake valve on each cylinder remains in the default, low-lift mode. When the duty cycle is high, more oil is passed through the solenoid and higher pressure develops in the oil line to the crankshaft. This causes the lift mechanism on the camshaft to go into high lift mode.
The oil line oil pressure sensor switch is normally closed or “on”. This applies when the engine is off or when running at low rpm. When the duty cycle of the solenoid is high and there should be high pressure in the oil line, the switch opens (“off”). (On my 2007, when I drive, the shift is in the 1600-1800 rpm range. When parked and just revving, it has to get over 3000 rpm before it shifts.)
On-board diagnostics monitor the state of the switch and compare this to the current intended take-off “mode”. If the target mode is “low lift” but the switch is “off”, or the mode is “high lift” and the switch is “on”, these are mismatches and will set P0026.
Note: The switch only monitors the pressure in the oil line to the camshaft lifter. It doesn’t actually check whether the mechanism itself is in low or high mode. It assumes that if the pressure is low, the mechanical system will hold the intake valve in the low-lift mode, and when the pressure is high, the mechanism will switch and hold the valve in the high-lift mode.
As mentioned, the criterion for mode change is engine speed, along with several other factors.
If the code does not appear at lower rpms (in your case down to about 100 – 110 kph) then basic AVLS operation is fine. However, at higher rpm, the pressure in the oil line between the solenoid and the camshaft seems to be dropping, causing the oil pressure sensor to change to “on” when it should remain “off”.
Loss of oil pressure in the AVLS crankshaft oil line can have several reasons, including a drop in engine oil pressure at higher rpm due to low or old, dirty oil (loss of viscosity ), a restricted or incorrect engine oil filter, a faulty oil pump or, in the case of the AVLS system, a faulty solenoid. Also, there is a small screen filter inside the mount on the back of the right side head that the solenoid is mounted to. If this filter is restricted by deposits, it can restrict oil flow to the camshaft lifter mechanism, and at higher engine speeds, drop it low enough for the pressure switch to trip.
