DTC P0155: Ho2S Bank 2 Sensor 1 Circuit - Heater Performance: Description

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

The Heated Oxygen Sensor (HO2S) heater is a device used in order to reduce the time that the sensor takes to go active. The Powertrain Control Module (PCM) controls the HO2S heaters using a high side driver, two low side drivers, and a current monitoring driver. The current monitoring driver tests the condition of the heaters. The high side driver provides the HO2S bank 1 sensor 1 heater with ignition voltage. A fused ignition feed provides bank 1 sensor 2, and bank 2 sensor 1 with ignition voltage. HO2S bank 1 sensor 1, and bank 2 sensor 1 receive ground through one of the low side drivers. HO2S bank 1 sensor 2 receives ground through a separate low side driver. With the engine running, the PCM turns ON the high side, and the low side drivers to warm the oxygen sensors. When the proper conditions are present, the PCM keeps the high side driver ON, turns ON the current monitor driver, and then turns OFF the warm-up driver. This allows the PCM to record a total current value for both of the fuel control heaters. If the test conditions remain stable, the PCM enters the second stage of the test. During this stage, the PCM keeps the current monitor ON, and turns OFF the high side driver. This allows the PCM to record a current value for the bank 2 sensor 1 heater circuit. The PCM subtracts the bank 2 sensor 1 current value from the total current value to determine the current value for bank 1 sensor 1. If the PCM detects a bank 2 sensor 1 current value outside the calibrated range, the Diagnostic Trouble Code (DTC) will set.