Heated Oxygen SEN (HO2S) Bank 1 SEN 1 & HO2S Bank 2 SEN 1

The heated oxygen sensor bank 1 sensor 1 (cylinders 1, 3, 5 which are closest to the front of dash) or heated oxygen sensor bank 2 sensor 1 (cylinders 2, 4, 6 which are closest to the radiator) are both located in each exhaust manifold bank. The L81 engine uses air/fuel ratio sensors called lambda sensors instead of the traditional voltage producing switching type sensors. The lambda sensors allow for a wider range of air/fuel control from around 8:1 to 18:1. Using these sensors, the ECM can maintain closed loop operation (using the oxygen sensor for fuel control) under all engine running conditions except cold engine start-up and extended decelerations.

The Scan tool provides a lambda value parameter for each of the two sensors. Lambda is described as the actual air/fuel ratio of the sensor divided by 14.7. For example, a lambda of 1.00 indicates that the sensor is detected a 14.7 to 1 air/fuel ratio. The higher the lambda value above 1.00, the leaner the exhaust the sensor is detecting. The lower the lambda value below 1.00, the richer the exhaust the sensor is detecting. Refer to the "Fuel Control' system description for a better understanding of how the hardware of these sensors work.

Each of the two lambda sensors contains a heater element controlled by the ECM necessary to speed up closed loop start times. The ECM will pulse the heater anytime the engine is running. The heater allows the sensor to become active within a maximum of 20 seconds after engine start at any ambient temperature if the sensor is functioning correctly.