Test Description

WARNING: This page is about a different car, the 1995 Oldsmobile Ninety-Eight and 1995 Buick Park Avenue. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Test numbers refer to numbers on diagnostic chart.

Visually/physically checking components/systems which may cause a rich condition may determine cause of Code P0172.
MAF sensor which causes PCM to read a higher then actual airflow can cause a rich condition, and Code P0172 to set.
Silicone contamination of Heated Oxygen Sensor (HO2S) can cause a false rich indication that will be sensed by PCM. PCM will then reduce amount of fuel delivered, possibly causing severe driveability symptoms.

Fig 1: Code P0172 Schematic (3.8L) Fuel Trim Rich

Fig 2: Code P0172 Diagnostic Flow Chart - 1 Of 2 (3.8L) Fuel Trim Rich

Fig 3: Code P0172 Diagnostic Flow Chart - 2 Of 2 (3.8L) Fuel Trim Rich