GM Low Pressure Signal
This bulletin applies to a number of GM vehicles produced between 2005 and 2010, equipped with an AFM (active fuel management) V8 engine. One example is the 2007-2009 Chevy Impala.
Some customers may complain of a low oil pressure message/light on the dash.
The technician may find DTC P0521 stored in the ECM. If this concern is encountered, follow service manual diagnosis. If it indicates that the Tech2 oil pressure parameter is low but proper oil pressure is present at the oil filter housing, before replacing any parts, inspect the valve lifter oil filter for debris/sludge that could be restricting oil flow to the oil pressure sensor.
Follow the valve lifter oil filter removal and installation procedure to remove the filter for inspection. If the filter is plugged, it can normally be cleaned with brake/contact cleaner and light shop air. If it cannot be cleaned, replace it. Do not replace the complete valve lifter oil manifold just because the filter is plugged.