Subaru P0026 or Subaru P0028
Diagnose and fix Subaru P0026 or Subaru P0028
Subaru 4-cylinder boxer engines are equipped with a variable valve lift feature to improve performance. The VVL system consists of two parts; an oil sensor switch and a VVL solenoid. A Subaru P0028 code refers to the Intake Valve Control Solenoid Circuit Range/Performance (Bank 2) and a Subaru P0026 refers to the Intake Valve Control Solenoid Circuit Range/Performance (Bank 1).
If you have either of these codes, start your diagnosis by looking for the signs of oil leakage at the oil pressure sensors. If you see oil leaking from the sensor, it must be replaced.
Test for P0026 or P0028
Unplug the connectors to the right and left bank oil pressure switches. Using a multimeter, check the reference voltage at each connector with the key in the RUN position (engine off). If the voltages match, that verifies the PCM is working and the wiring harness is in good condition. If you don’t see voltage or the voltages don’t match, look for an open or short to ground in the wiring harness.
Next, reconnect the connectors to the oil pressure switches. Then backprobe each connector. The voltage should read 0-volts since these are normally closed switches that pull the reference voltage to ground.
At 4,000 RPM the oil pressure switch opens, so you’ll see the reference voltage again.
If you don’t see that voltage switch, replace the oil sensing switch. The switch is a common failure on these engines.
WARNING: Do not over-tighten the oil pressure switch. Over-tightening can crack the cylinder head
How the variable valve lift system works
The variable valve lift system on the Subaru SOHC engine is designed to improve fuel efficiency, increase engine output, and decrease emissions.
The system works by changing the lift amount of intake valve to low-lift or high-lift according to the engine driving status.
The low and hi valve lift arms are actuated by the Variable Valve Timing Solenoid that pulses oil pressure to activate the locking pin to the high lift arm
If the solenoid fails, you’d see a P0076, P0077, or P0082 trouble code.
©, 2022 Rick Muscoplat
Posted on by Rick Muscoplat