Uploaded April 2026 | Updated September 2026, 3 weeks ago

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This Subaru Forester came in with an intermittent P0028, but this video turns into a much bigger lesson than just finding the fault.

The real value here is the troubleshooting process: how to test an output when you do not have bidirectional controls, how to identify a power-side switched solenoid circuit, how to manually energize the actuator safely, and how to confirm switch input operation without blindly following the OEM flowchart.

In this case, the flowchart was absolutely ridiculous and you would have never found this fault by using it. Understanding circuit operation made the diagnosis faster and more accurate.

Timestamps
00:00 Intro, symptoms, and intermittent P0028 overview
01:35 Bank identification and confirming the fault is on the left side
02:57 No bidirectional controls available, so testing old-school
03:40 Comparing left/right solenoid duty cycle and current flow
05:29 Solenoid and pressure switch location and system operation
05:58 Unplugging the opposite side to verify scan data
07:12 Wiggle testing and checking for harness/current drop issues
07:51 Scope testing the circuit and identifying a power-side switched output
09:47 Manually energizing the solenoid and watching switch response
12:00 Why applying battery voltage here will not damage the driver
16:29 Why both solenoid wires go to the ECM: current monitoring discussion
19:23 Clearing induced codes and confirming the fault is intermittent
21:19 What to do when the fault is gone: clear it and drive it
22:02 Teaching segment: output testing and switch input fundamentals
25:00 Why circuit identification gets muddy when both wires go to the ECM
33:02 Confirming pressure switch operation and bypass testing the input
40:20 Why the OEM flowchart is inefficient and misses the real test
47:47 Manually energizing the circuit again and catching the fault live
49:42 Proving the pressure switch is stuck open with the engine off
53:16 Final diagnosis: sticking variable valve lift diagnosis pressure switch

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