DTC P0161: Ho2S Heater Circuit Performance - Bank 2, Sensor 2: Description

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The Heated Oxygen (HO2S) bank 2 sensor 2 is threaded into the front exhaust pipe directly behind the cylinder 2, 4, 6 pre-converter (cylinders 2, 4, 6 are closest to front of dash). The sensor is used by the ECM to determine the oxygen storage capability of the pre-converter, fuel trim biasing (time held lean or rich) and certain techniques used to diagnose DTCs associated with the pre-catalyst oxygen sensor. The sensor is equipped with a heater to provide additional heat to speed up sensor activation time. The ECM calculates the efficiency of the sensor heating element by calculating the internal sensor (not heater) resistance based on actual current and signal voltage measurements on Purple wire after the engine has been running a certain length of time. As temperature increases, the sensor internal resistance will decrease. The ECM compares modeled sensor resistance values to the measured values based on the calculated sensor temperature (exhaust gas temperature). If the heater is working properly, the internal sensor resistance will decrease at a certain rate based on the exhaust gas temperature. If the resistance takes too long to decrease or is too high after a certain amount of engine run time, the heater is assumed to be heating insufficiently. DTC P0161 will set if the calculated internal sensor resistance is too high after a certain length of engine run time indicating an inefficient heating element.