Air Intake Restriction Gauge
The air intake restriction gauge indicates the vacuum on the engine side of the air cleaner. On standard installations, it is mounted on the air intake duct in the engine compartment. See Fig.. As an option for easier viewing, the intake-air restriction indicator can be mounted on the dash, usually on the right-hand control panel.
Fig. 1, Air Intake Restriction Indicator
Air intake restriction vacuum is measured in inches of water (inH2O). For vehicles equipped with a graduated indicator or a restriction gauge on the dash, check the gauge with the engine off. If the yellow signal stays locked in the red zone once the engine is shut down, or is at or above 25 inH 2 O, the air cleaner element needs to be replaced.
Note: Rain or snow can wet the filter and cause a temporarily higher than normal reading.