What size is the oxygen sensor on a Lexus IS250?
The oxygen sensors on a Lexus IS250 use an 18 mm diameter thread with a 1.5 mm pitch (M18x1.5). The IS250 has four sensors in total: two upstream sensors before the catalytic converter and two downstream sensors after it, one on each exhaust bank.
For model-year context, the IS250's four sensors share the same basic thread size, which simplifies sourcing replacements. The sensor bodies typically use a 22 mm (7/8 inch) hex for installation and removal, though you should always verify the exact part by sensor position and bank when ordering.
Thread size and sensor locations
The following overview explains the sensor positions and how they correspond to the IS250’s exhaust layout:
Upstream vs downstream sensors
Upstream sensors (before the catalytic converter) monitor fuel and exhaust gas composition prior to treatment, while downstream sensors (after the catalytic converter) monitor the efficiency of the catalytic converter. On the IS250, there are two banks (Bank 1 and Bank 2), each with one upstream and one downstream sensor.
The following list identifies the four sensors by bank and position to help you identify the correct replacement part:
- Bank 1 Sensor 1 (B1S1) — upstream sensor on Bank 1, before the catalytic converter
- Bank 1 Sensor 2 (B1S2) — downstream sensor on Bank 1, after the catalytic converter
- Bank 2 Sensor 1 (B2S1) — upstream sensor on Bank 2, before the catalytic converter
- Bank 2 Sensor 2 (B2S2) — downstream sensor on Bank 2, after the catalytic converter
The four sensors share the same thread size (M18x1.5); this means you generally order the appropriate upstream and downstream sensors for each bank, ensuring you select the correct bank labeling when purchasing.
What to know when replacing
When replacing IS250 oxygen sensors, use sensors that match the factory specifications and follow the OEM guidance on installation torque and any anti-seize recommendations. If you’re replacing multiple sensors, confirm which ones triggered the diagnostic codes to avoid unnecessary replacements.
Summary
The oxygen sensors on a Lexus IS250 use an M18x1.5 thread (18 mm diameter, 1.5 mm pitch). There are four sensors in total—two upstream and two downstream—one for each exhaust bank. Always verify the sensor position (Bank 1 or Bank 2 and upstream vs downstream) when ordering replacements to ensure you get the correct part.
