Subaru Forester O2 Sensor Malaysia

The Subaru Forester SJ (2013–2018) and SK (2019+) are popular AWD SUVs in Malaysia using the FB25 2.

Subaru Forester O2 Sensor

Forester O2 sensor configuration: FB25 has 2 O2 sensors per bank — upstream (pre-cat, primary lambda sensor) controls fuel trim; downstream (post-cat) monitors catalytic converter efficiency; 4-cylinder means 2 sensors total
Forester upstream O2 sensor: P0130 (circuit malfunction), P0131/P0132 (voltage out of range), P0133 (slow response) — all upstream O2 sensor faults; slow response sensor (P0133) causes poor fuel economy and emissions; replace at 80,000–100,000 km
Forester downstream O2 sensor: P0420 (catalyst efficiency below threshold) uses downstream sensor data; if downstream sensor reads same voltage as upstream — catalyst is dead; P0420 fix = replace catalytic converter; downstream O2 itself rarely fails on FB25
Forester O2 sensor replacement: use OEM (Denso or NGK NTK) O2 sensor for correct Subaru voltage response; some aftermarket sensors have incorrect mV range causing persistent code after replacement; Denso NTK recommended for Subaru