Diagnostic Aids
WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
These DTCs use two-trip detection logic. When DTC P0171 exists, the actual air/fuel ratio is to lean. When DTC P0172 exists, the actual air/fuel ratio is to rich. If total of short-term fuel trim value and long-term fuel trim value is within plus or minus 38 percent, the system is functioning normally. Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.