DTC P0135: Ho2S Bank 1, Sensor 1 Heater Circuit: Description

WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

Heating elements inside the Heated Oxygen Sensors (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The HO2S heater operation is controlled by the Powertrain Control Module (PCM). A high side driver supplies ignition power to the bank 1 HO2S 1, and is equipped with a current monitor. There are 2 low side drivers that provide the heater ground path. The bank 2 HO2S 1 is supplied power from the external ignition 1 voltage circuit, and uses the same low side drivers. When the ignition switch is turned on the PCM performs an HO2S heater circuit check using the high side driver current monitor circuit. When the engine is started, all 3 drivers are switched on. One of the low drivers is for heater warm-up only, and is used until the proper heater temperature is reached. When the warm-up low driver is switched off, the heater ground path is controlled through the remaining low side driver. The PCM now records the total heater circuit current, if the heater current remains stable the PCM momentarily turns off the high side driver. The PCM now records the bank 2 HO2S 1 current. This value is subtracted from the previously recorded total and is used to determine the condition of the heater circuit. If the PCM detects a HO2S bank 1 sensor 1 heater current outside of the calibrated range, DTC P0135 will set.